NOW HEAR THIS...

 The change came over Lucky. His darkbrown eyes turned hard. Every muscleof Lucky's tall body seemed tense.

 "Commander Donahue," Lucky said,"I am responsible omy to the head of theCouncil of Science and to the Presidentof the Solar Federation of Worlds. Ioutrank you and yon will .be bound bymy decisions and orders.

 "The warning yon have just given me is evidence of your own incompetence.You are obviously not In control of yourmen and not fit to command men. Nowhear this: I will land on Jupiter Nineand I will conduct my Investigations. Iwill handle your men if yon cannot.''

 He paused while the other gasped. "Doyou understand, Commander?"

 By Isaac Aslmov

 Published by Ballantine Books:

 THE CLASSIC FOUNDATION SERIES:Foundation

 Foundation and EmpireSecond Foundation Foundation's Edge

 THE GALACTIC EMPIRE HOVELS;The Stars, Like DustThe Currents Of Space Pebble In TheSky

 THE CAVES OF STEEL

 THE NAKED SUN

 I, ROBOT

 THE WINDS OF CHANGE

 THE LUCKY STARR ADVENTURES:David Starr—Space RangerLucky Starr and the Pirates of the AsteroidsLucky Starr and the Oceans of VenusLucky Starr and the Big Sun of MercuryLucky Starr and the Moons of Jupiter Lucky Starr and the Rings of Saturn

 LUCKY STARRAND THE

 MOONS OF

 JUPITER

 Isaac Asimov

A Del Rey Book

 BALLANTINE BOOKS • MEW YORK	

 writing as Paul French

 VL: 7 + up RLL:IL: 8 + up

 A Del Rey Book

 Published by Ballantine Books

 Copyright © 1957 by Doubleday and Company, Inc.Preface Copyright © 1978 by Isaac Asimov

 All rights reserved under International and Pan-American CopyrightConventions. Published in the United States by Ballantine Books, a division of Random House, Inc., New York, and simultaneouslyin Canada by Random House ofCatiada Limited, Toronto.

 All the characters in this book are fictitious, and any resemblanceto actual persons living or dead is purely coincidental.

 ISBN 0-345-31623-1

 This edition published by arrangement withDoubleday and Company, Inc.

 Manufactured in the United States of AmericaFirst Ballantine Books Edition: August 1984Cover art by David B. Mattingly

CONTENTS	

1	
Trouble on Jupiter Nine	
9	

2	
The Commander Is Angry	
19	

3	
The Agrav Corridor	
29	

4	
Initiation!	
41	

5	
Needle-Guns and Neighbors	
51	

6	
Death Enters the Game	
63	

7	
A Robot Enters the Game	
73	

8	
Blindness	
83	

9	
The Agrav Ship	
93	

10	
In the Vitals of the Ship	
103	

11	
Down the Line of Moons	
113	

12	
The Skies and Snows of Io	
123	

13	
Fall!	
135	

14	
Jupiter Close-up	
145	

15	
Traitor!	
157	

16	
Robot!	
167	

 Preface

 Back in the 1950s, I wrote a series of six derring-donovels about David "Lucky" Starr and his battles against malefactors within the Solar System. Each of the six took place in a different region of the systemand in each case I made use of the astronomicalfacts—as they were then known.

 Now more than a quarter-century later, these novelsare being published in new editions; but what a quarter-century it has been! More has been learned about theworlds of our Solar System in this last quarter-centurythan in all the thousands of years that went before.

 LUCKY STARR: AND THE MOONS OF JUPITERwas written in 1956. In late 1973, however, theJupiter-probe, Pioneer X, passed by Jupiter and re­corded an enormous magnetic field containing denseconcentrations of charged particles. The large satellitesof Jupiter are buried in that field and the intensity of radiation would certainly make it difficult or even impossible for manned ships to maneuver in their neighborhood.

 Lucky's trip through the satellite system wouldhave to be adjusted to take the intense radiation intoaccount if I were writing the book today. And in1974, a 13th satellite of Jupiter, was discovered, a very small one only a few miles across, with an orbit quite similar to that of Jupiter-IX. I'd have mentionedit if I were doing the book now.

 7

 8                       

 I hope my Gentle Readers enjoy the book anyway,as an adventure story, but please don't forget thatthe advance of science can outdate even the mostconscientious science-fiction writer and that my astronomical descriptions are no longer accurate inall respects.

 isaac asimov

 1

 Trouble on Jupiter Nine

 Jupiter was almost a perfect circle of creamy light,half the apparent diameter of the moon as seen fromEarth, but only one seventh as brightly lit because ofits great distance from the sun. Even so, it was abeautiful and impressive sight.

 Lucky Starr gazed at it thoughtfully. The lights inthe control room were out and Jupiter was centered on the visiplate, its dim light making Lucky and his com­panion something more than mere shadows. Luckysaid, "If Jupiter were hollow, Bigman, you coulddump thirteen hundred planets the size of Earth intoit and still not quite fill it up. It weighs more than allthe other planets put together."

 John Bigman Jones, who allowed no one to call himanything but Bigman, and who was five feet two inchestall if he stretched a little, disapproved of anything that was big, except Lucky. He said, "And what good is allof it? No one can land on it. No one can come near it."

 "We'll never land on it, perhaps," said Lucky, "butwe'll be coming close to it once the Agrav ships aredeveloped."

 9

 10                        

 "With the Sirians on the job," said Bigman, scowlingin the gloom, "it's going to takems to make sure thathappens."

 "Well, Bigman, we'll see."

 Bigman pounded his small right fist into the open palm of his other hand. "Sands of Mars, Lucky, how long do we have to wait here?"

 They were in Lucky's ship, theShooting Starr, whichwas in an orbit about Jupiter, having matched veloci­ties with Jupiter Nine, the giant planet's outermostsatellite of any size.

 That satellite hung stationary a thousand milesaway. Officially, its name was Adrastea, but exceptfor the largest and closest, Jupiter's satellites weremore popularly known by numbers. Jupiter Nine wasonly eighty-nine miles in diameter, merely an asteroid,really, but it looked larger than distant Jupiter, fifteenmillion miles away. The satellite was a craggy rock,gray and forbidding in the sun's weak light, and scarcely worth interest. Both Lucky and Bigman hadseen a hundred such sights in the asteroid belt.

 In one way, however, it was different. Under its skina thousand men and billions of dollars labored to pro­duce ships that would be immune to the effects ofgravity.

 Nevertheless, Lucky preferred watching Jupiter. Even at its present distance from the ship (actuallythree fifths of the distance of Venus from Earth atthen closest approach), Jupiter showed a disc large enough to reveal its colored zones to the naked eye.They showed in fault pink and greenish-blue, asthough a child had dipped Ms fingers in a watery paintand trailed them across Jupiter's image.

                                                                                 11

 Lucky almost forgot the deadliness of Jupiter in itsbeauty. Bigman had to repeat his question in a loudervoice.

 "Hey, Lucky, how long do we have to wait here?"

 "You know the answer to that, Bigman. Until Com­mander Donahue comes to pick us up."

 "I know that part. What I want to know is why wehave to wait for him."

 "Because he's asked us to."

 "Oh, he has. Who does the cobber think he is?"

 "The head of the Agrav project," Lucky said pa­tiently.

 "You don't have to do what he says, you know, evenif he is."

 Bigman had a sharp and deep realization of Lucky'spowers. As full member of the Council of Science,that selfless and brilliant organization that fought the enemies of Earth within and without the solar system,Lucky Starr could write his own ticket even against themost high-ranking.

 But Lucky was not quite ready to do that. Jupiterwas a known danger, a planet of poison and unbear­able gravity; but the situation on Jupiter Nine wasmore dangerous still because the exact points of dangerwere unknown—and until Lucky could know a bitmore, he was picking his way forward carefully.

 "Be patient, Bigman," he said.

 Bigman grumbled and flipped the lights on. "We'renot staring at Jupiter all day, are we?"

 He walked over to the small Venusian creaturebobbing up and down in its enclosed water-filled cagein the corner of the pilot room. He peered fondlydown at it, his wide mouth grinning with pleasure. The

 12                        

 V-frog always had that effect on Bigman, or indeed,on anyone.

 The V-frog was a native of the Venusian oceans,*a tiny thing that seemed, at times, all eyes and feet. Itsbody was green and froglike and but six inches long.His twa big eyes protruded like gleaming blackberries, and its sharp, strongly curved beak opened and closed at irregular intervals. At the moment its six legs wereretracted, so that the V-frog hugged the bottom of itscage, but when Bigman tapped the top cover, they un­folded like a carpenter's rule and became stilts. ^

 It was an ugly little thing but Bigman loved it whenhe was near it. He couldn't help it. Anyone else wouldfeel the same. The V-frog saw to that.

 Carefully Bigman checked the carbon-dioxide cylin­der that kept the V-frog's water well saturated and healthful and made sure that the water temperature inthe cage was at ninety-five. (The warm oceans of Venuswere bathed by and saturated with an atmosphere ofnitrogen and carbon dioxide. Free oxygen, nonexistenton Venus except in the man-made domed cities at thebottom of its ocean shallows, would have been mostuncomfortable for the V-frog.)

 Bigman said, "Do you think the weed supply is enough?" and as though the V-frog heard the remark,its beak snipped a green tendril off the native Venusian weed that spread through the cage, and chewed slowly.

 Lucky said, "It will hold till we land on JupiterNine," and then both men looked up sharply as thereceiving signal sounded its unmistakable rasp.

 A stern, aging face was centered on the visiplate

 * SeeLucky Starr and the Oceans of Venus.

                                                                                13

 after Lucky's fingers had quickly made the necessaryadjustments.

 "Donahue at this end," said a voice briskly.

 "Yes, Commander," said Lucky. "We've been wait­ing for you."

 "Clear locks for tube attachment, then."

 On the commander's face, written in an expressionas clear as though it consisted of letters the size ofClass I meteors, was worry—trouble and worry.

 Lucky had grown accustomed to just that expres­sion on men's faces in these past weeks. On ChiefCouncilman Hector Conway's for instance. To thechief councilman, Lucky was almost a son and theolder man felt no need to assume any pretense of con­fidence.

 Conway's rosy face, usually amiable and self-as­sured under its crown of pure white hair, was set in atroubled frown. ''I've been waiting for a chance totalk to you for months."

 'Trouble?" Lucky asked quietly. He had just re­turned from Mercury less than a month earlier, andthe intervening time had been spent in his New Yorkapartment. "I didn't get any calls from you."

 "You earned your vacation," Conway said gruffly."I wish I could afford to let it continue longer."

 "Just what is it, Uncle Hector?"

 The chief councilman's old eyes stared firmly intothose of the tall, lithe youngster before him and seemedto find comfort in those calm, brown ones. "Sirius!"he said.

 Lucky felt a stir of excitement within him. Was it the great enemy at last?

 It had been centuries since the pioneering expedi-

 14                        

 tions from Earth had colonized the planets of thenearer stars. New societies had grown up on thoseworlds outside the solar system. Independent societiesthat scarcely remembered their Earthly origin.

 The Sirian planets formed the oldest and strongestof those societies. The society had grown up on newworlds where an advanced science was brought to bearon untapped resources. It was no secret that the Sirianss strong in the belief that they represented the best ofmankind, looked forward to the time when they mightrule all men everywhere; and that they considered Earth, the old mother world, their greatest enemy.

 In the past they had done what they could to sup­port the enemies of Earth at home* but never yet hadthey felt quite strong enough to risk open war.

 But now?

 "What' s this about Sinus?" asked Lucky.

 Conway leaned back. His fingers drummed lightlyon the table. He said, "Sirius grows stronger each year.We know that But their worlds are underpopulated;they have only a few millions. We still have more human beings in our solar system than exist in all the galaxy besides. We have more ships and more scien­tists; we still have the edge. But, by Space, we won'tkeep that edge if things keep on as they've been going."

 "In what way?"

 "The Sirians are finding out things. The Council hasdefinite evidence that Sirius is completely up-to-dateon our Agrav research."

 "What!" Lucky was startled. There were few thingsmore top-secret than the Agrav project. One of the reasons actual construction had been confined to one of the outer satellites of Jupiter had been for the sake

 * SeeLucky Starr and the Pirates of the Asteroids.

                                                                                15

 of better security. "Great Galaxy, how has that hap­pened?"

 Conway smiled bitterly. "That is indeed the ques­tion. How has that happened? All sorts of material areleaking out to them, and we don't know how. TheAgrav data is most critical. We've tried to stop it.There isn't a man on the project that hasn't been thor­oughly checked for loyalty. There isn't a precaution wehaven't taken. Yet material still leaks. We've plantedfalse data and that's gone out. We know it has from our own Intelligence information. We've planted datain such ways that itcouldn't go out, and yet it has."

 "How do you meancouldn't go out?"

 "We scattered it so that no one man—in fact, nohalf dozen men—could possibly be aware of it all. Yetit went. It would mean that a number of men would have to be co-operating in espionage and that's justunbelievable."

 "Or that some one man has access everywhere,"said Lucky.

 "Which is just as impossible. It must be something new, Lucky. Do you see the implication? If Sirius haslearned a new way of picking our brains, we're nolonger safe. We could never organize a defense againstthem. We could never make plans against them."

 "Hold it, Uncle Hector. Great Galaxy, give yourselfa minute. What do you mean when you say they'repicking our brains?" Lucky fixed his glance keenly on the older man.

 The chief councilman flushed. "Space, Lucky, I'mgetting desperate. I can't see how else this can be done.The Sirians must have developed some form of mindreading, of telepathy."

 "Why be embarrassed at suggesting that? I suppose

 16                        

 it's possible. We know of one practical means of telep­athy at least. The Venusian V-frogs."

 "All right," said Conway. "I've thought of that, too,but they don't have Venusian V-frogs. I know what'sbeen going on in V-frog research. It takes thousands ofthem working in combination to make telepathy pos­sible. To keep thousands of them anywhere but onVenus would be awfully difficult, and easily detectable,too. And without V-frogs, there is no way of manag­ing telepathy."

 "No way we've worked out," Lucky said softly, "sofar. It is possible that the Sirians are ahead of us intelepathy research."

 "Without V-frogs?"

 "Even without V-frogs."

 "I don't believe it," Conway cried violently. "I can'tbelieve that the Sirians can have solved any problem that has left the Council of Science so completelyhelpless."

 Lucky almost smiled at the older man's pride in theorganization, but had to admit that there was some­thing more than merely pride there. The Council ofScience represented the greatest collection of intellectthe galaxy had ever seen, and for a century not one sizable piece of scientific advance anywhere in theGalaxy had come anywhere but from the Council.

 Nevertheless Lucky couldn't resist a small dig. Hesaid, "They're ahead of us in robotics."

 "Not really," snapped Conway. "Only in its applica­tions. Earthmen invented the positronic brain thatmade the modern mechanical man possible. Don'tforget that. Earth can take the credit for all the basic developments. It's just that Sinus builds more robots

                                                                                 17

 and," he hesitated, "has perfected some of the engineer­ing details."

 "So I found out on Mercury," Lucky said grimly.*

 "Yes, I know, Lucky. That was dreadfully close."

 "But it's over. Let's consider what's facing us now.The situation is this: Sinus is conducting successfulespionage and we can't stop them."

 "Yes."

 "And the Agrav project is most seriously affected."

 "Yes."

 "And I suppose, Uncle Hector, that what you wantme to do is to go out to Jupiter Nine and see if I canlearn something about this."

 Conway nodded gloomily. "It's what I'm asking youto do. It's unfair to you. I've gotten into the habit ofthinking of you as my ace, my trump card, a man Ican give any problem and be sure it will be solved. Yetwhat can you do here? There's nothing Council hasn'ttried and we've located no spy and no method of espionage. What more can we expect of you?"

 "Not of myself alone. I'll have help."

 "Bigman?" The older man couldn't help smiling.

 "Not Bigman alone. Let me ask you a question. Toyour knowledge, has any information concerning ourV-frog research on Venus leaked out to the Sirians?"

 "No," said Conway. "None has, to my knowledge."

 "Then I'll ask to have a V-frog assigned to me."

 "A V-frog! One V-frog?"

 "That's right."

 "But what good win that do you? The mental fieldof a single V-frog is terribly weak. You won't be ableto read minds."

 * SeeLucky Starr and the Big Sun of Mercury.

 18                        

 "True, but I might be able to catch whiffs of strongemotion."

 Conway said thoughtfully, "You might do that. Butwhat good would that do?"

 ''I'm not sure yet. Still, it will be an advantageprevious investigators haven't had. An unexpectedemotional surge on the part of someone there mighthelp me, might give me grounds for suspicion, mightpoint the direction for further investigation. Then,too—"

 "Yes?"

 "If someone possesses telepathic power, developedeither naturally or by use of artificial aids, I mightdetect something much stronger than just a whiff ofemotion. I might detect an actual thought, some dis­tinct thought, before the individual learns enoughfrom my mind to shield his thoughts. You see what Imean?"

 "He could detect your emotions, too."

 "Theoretically, yes, but I would be listening foremotion, so to speak. He would not."

 Conway's eyes brightened. "It's a feeble hope, but,by Space, it's a hope! I'll get you your V-frog . . .But one thing, David," and it was only at momentsof deep concern that he used Lucky's real name, theone by which the young councilman had been knownall through childhood—"I want you to appreciate theimportance of this. If we don't find out what the Siriansare doing, it means they are really ahead of us at last.Andthat means war can't be delayed much longer.War or peace hangs on this."

 "I know," said Lucky softly.

 2

 The Commander Is Angry

 And so it came about that Lucky Starr, Earthman,and his small friend, Bigman Jones, born and bred onMars,* traveled beyond the asteroid belt and intothe outer reaches of the solar system. And it was forthis reason also that a native of Venus, not a man atall, but a small mind-reading and mind-influencinganimal, accompanied them.

 They hovered, now, a thousand miles above JupiterNine and waited as a flexible conveyer tube was made fast between theShooting Starr and the commander'sship. The tube linked air lock to air lock and formeda passageway which men could use in going from oneship to the other without having to put on a spacesuit. The air of both ships mingled, and a man usedto space, taking advantage of the absence of gravity,could shoot along the tube after a single initial push and guide himself along those places where the tubecurved with the gentle adjusting force of a well-placedelbow.

 * SeeDavid Starr, Space Ranger.

 19

 20                        

 The commander's hands were the first part of himvisible at the lock opening. They gripped the lip ofthe opening and pushed in such a way that the com­mander himself leapfrogged out and came down intheShooting Starr's localized artificial gravity field (orpseudo-grav field, as it was usually termed) withscarcely a stagger. It was neatly done, and Bigman,who had high standards indeed for all forms of space­men's techniques, nodded in approval.

 "Good day, Councilman Starr," said Donahuegruffly. It was always a matter of difficulty whetherto say "good morning," "good afternoon," or "good evening" in space, where, strictly speaking, there wasneither morning, afternoon, nor evening. "Good day" was the neutral term usually adopted by spacemen.

 "Good day, Commander," said Lucky. "Are thereany difficulties concerning our landing on Jupiter Ninethat account for this delay?"

 "Difficulties? Well, that's as you look at it." Helooked about and sat down on one of the small pilot'sstools. 'Tve been in touch with Council headquartersbut they say I must treat with you directly, so I'mhere."

 Commander Donahue was a wiry man, with an airof tension about him. His face was deeply lined, hishair grayish but showing signs of having once beenbrown. His hands had prominent blue veins along theirbacks, and he spoke in an explosive fashion, rappingout his phrases in a quick succession of words.

 "Treat with me about what, sir?" asked Lucky.

 "Just this, Councilman. I want you to return toEarth."

 "Why, sir?"

                                                                                21

 The commander did not look directly at Lucky ashe spoke. "We have a morale problem. Our men havebeen investigated and investigatedand investigated.They've all come through clear each time, and eachtime a new investigation is started. They don't like it and neither would you. They don't like being undercontinual suspicion. And I'm completely on their side. Our Agrav ship is almost ready and this is not the timefor my men to be disturbed. They talk of going onstrike."

 Lucky said calmly, "Your men may have beencleared but there is still leakage of information."

 Donahue shrugged. "Then it must come from else­where. It must..." He broke off and a sudden incon­gruous note of friendliness entered his voice. "What'sthat?"

 Bigman followed his eyes and said at once, "That'sour V-frog, Commander, I'm Bigman."

 The commander did not acknowledge the introduc­tion. He approached the V-frog instead, staring intothe enclosed water-filled cage. "That's a Venus crea­ture, isn't it?"

 "That's right," said Bigman.

 "I've heard of them. Never saw one, though. Cutelittle jigger, isn't it?"

 Lucky felt a grim amusement. He did not find itstrange that in the midst of a most serious discussionthe commander should veer off into an absorbed ad­miration for a small water creature from Venus. TheV-frog itself made that inevitable.

 The small creature was looking back at Donahuenow out of its black eyes, swaying on its extensible legsand clicking its parrot beak gently. In all the known

 22                        

 universe its means of survival was unique. It had nodefensive weapons, no armor of any sort. It had noclaws or teeth or horns. Its beak might bite, but eventhat bite could do no harm to any creature largerthan itself.

 Yet it multiplied freely along the weed-coveredsurface of the Venusian ocean, and none of the fiercepredators of the ocean's deeps disturbed it, simplybecause the V-frog could control emotion. They in­stinctively caused all other forms of life to like them,to feel friendly toward them, to have no wish what­ever to hurt them. So they survived. They did morethan that. They flourished.

 Now this particular V-frog was filling Donahue,quite obviously, with a feeling of friendliness, so thatthe army man pointed a finger at it through the glassof its cage and laughed to see it cock its head andsink down along its collapsing legs, as Donahue movedhis finger downward.

 "You don't suppose we could get a few of these forJupiter Nine, do you, Starr?" he asked. "We're greatones for pets here. An animal here and there makesfor a breath of home."

 "It's not very practical," said Lucky. "V-frogs aredifficult to keep. They have to be maintained in acarbon-dioxide-saturated system, you know. Oxygenis mildly poisonous to them. That makes things com­plicated."

 "You mean they can't be kept in an open fish-bowl?"

 "They can be at tunes. They're kept so on Venus,where carbon dioxide is dirt cheap and where theycan always be turned loose in the ocean if they seemto be unhappy. On a ship, though, or on an airless

                                                                                23

 world, you don't want to bleed carbon dioxide con­tinuously into the air, so a closed system is best."

 "Oh." The commander looked a bit wistful.

 "To return to our original subject of discussion,"said Lucky briskly, "I must refuse your suggestionthat I leave. I have an assignment and I must carryit through."

 It seemed to take a few seconds for the commanderto emerge from the spell cast by the V-frog. His facedarkened. "I'm sure you don't understand the entire situation." He turned suddenly, looking down at Big-man. "Consider your associate, for instance."

 The small Martian, with a stiffening of spine, be­gan to redden. "I'm Bigman," he said. "I told you thatbefore."

 "Not very big a man, nevertheless," said the com­mander.

 And though Lucky placed a soothing hand on thelittle fellow's shoulder at once, it didn't help. Bigmancried, "Bigness isn't on the outside, mister. My nameis Bigman, and I'm a big man against you or anyoneyou want to name regardless of what the yardsticksays. And if you don't believe it. . ." He was shrug­ging his left shoulder vigorously. "Let go of me, Lucky,will you? This cobber here..."

 "Will you wait just one minute, Bigman?" Luckyurged. "Let's find out what the commander is tryingto say."

 Donahue had looked startled at Bigman's suddenverbal assault. He said, "I'm sure I meant no harmin my remark. If I've hurt your feelings, I'm sorry."

 "My feelings hurt?" said Bigman, his voice squeak­ing. "Me? Listen, one thing about me, I never lose

 24                        

 my temper and as long as you apologize, we'll forgetabout it." He hitched at his belt and brought thepalms of his hands down with a smart slap againstthe knee-high orange and vermilion boots that werethe heritage of his Martian farm-boy past and withoutwhich he would never be seen in public (unless hesubstituted others with an equally garish color scheme).

 "I want to be very plain with you, Councilman,"said Donahue, turning to Lucky once more. "I havealmost a thousand men here at Jupiter Nine, andthey're tough, all of them. They have to be. They'refar from home. They do a hard job. They run greatrisks. They have their own outlook on life now andit's a rough one. For instance, they haze newcomers and not with a light hand, either. Sometimes new­comers can't stand it and go home. Sometimes they're hurt. If they come through, everything's fine."

 Lucky said, "Is this officially permitted?"

 "No. But it is permitted unofficially. The men haveto be kept happy somehow, and we can't afford toalienate them by interfering with their horseplay. Goodmen are hard to replace out here. Not many peopleare willing to come to the moons of Jupiter, you know.Then, too, the initiation is helpful in weeding out the misfits. Those that don't pass would probably fail hiother respects eventually. That is why I made mention of your friend."

 The commander raised his hands hurriedly. "Nowmake no mistake. I agree that he is big on the insideand capable and anything else you want. But will hebe a match for what lies ahead? Will you, Council­man?"

 "You mean the hazing?"

 25

 "It will be rough, Councilman," said Donahue. "The men know you are coming. News gets around some­how."

 "Yes, I know," murmured Lucky.

 The commander scowled. "In any case, they knowyou are to investigate them and they will feel no kind­ness toward you. They are in an ugly mood and theywill hurt you, Councilman Starr. I am asking you not to land on Jupiter Nine for the project's sake, for my men's sake, and for your own. There you have it asplainly as I can put it."

 Bigman stared at the change that came over Lucky.His usual look of calm good nature was gone. His darkbrown eyes turned hard, and the straight lines of hislean and handsome face were set in something that Big­man rarely saw there: bitter anger. Every muscle of Lucky's tall body seemed tense.

 Lucky said ringingly, "Commander Donahue, I am amember of the Council of Science. I am responsibleonly to the head of the Council and to the President of the Solar Federation of Worlds. I outrank you and you will be bound by my decisions and orders.

 "I consider the warning you have just given me tobe evidence of your own incompetence. Don't say any­thing, please; hear me out. You are obviously not incontrol of your men and not fit to command men. Nowhear this: I will land on Jupiter Nine and I will con­duct my investigations. I will handle your men if youcannot."

 He paused while the other gasped and vainly at­tempted to find his voice. He rapped out, "Do you understand, Commander?"

 26                        

 Commander Donahue, his face congested almost be­yond recognition, managed to grind out, "I will takethis up with the Council of Science. No arrogant youngwhipsnap can talk like that to me, councilman or nocouncilman. I will match my record as a leader of menagainst that of anyone in the service. Furthermore, mywarning to you will be on record also and if you arehurt on Jupiter Nine, I will run the risk of court-martialgladly. I will do nothing for you. In fact, I hope—Ihope they teach you manners, you..."

 He was past speech once more. He turned on hisheel, toward the open lock, connected still with thespace tube to bis own ship. He clambered in, missing ahand hold in his anger and stumbling badly,

 Bigman watched with awe as the commander's heelsdisappeared down the tube. The other's anger hadbeen so intense a thing that the little Martian hadseemed to feel it in his own mind as though waves of heat were rolling in upon him.

 Bigman said, "Wow, that cobber was reallygoing!You had him rocking."

 Lucky nodded. "He was angry. No doubt about it."

 Bigman said, "Listen, maybehe's the spy. He'd knowthe most. He'd have the best chance."

 "He'd also be the most thoroughly investigated, so your theory is doubtful. But at least he's helped us outin a little experiment, so when I see him next I willhave to apologize."

 "Apologize?" Bigman was horrified. It was his firmview that apologies were strictly something that otherpeople had to do. "Why?"

 "Come, Bigman, do you suppose I really meant thosethings I said?"

                                                                                27

 "You weren't angry?"

 "Not really."

 "It was an act?"

 "You could call it that. I wanted to make him angry,really angry, and 1 succeeded. I could tell that first­hand."

 "Firsthand?"

 "Couldn't you? Couldn't you feel the anger just pour­ing out of him all over you?"

 "Sands of Mars! The V-frog!"

 "Of course. It received the commander's anger andrebroadcast it on to us. I had to know if one V-frogcould do it. We tested it back on Earth, but until I triedit under actual field conditions, I wasn't sure. Now Iam."

 "It broadcast fine."

 "I know. So at least it proves we have a weapon, oneweapon, after all."

 3

 The Agrav Corridor

 "Good deal," said Bigman fiercely. "Then we're onour way."

 "Hold it," said Lucky at once. "Hold everything, myfriend. This is a non-specific weapon. We'll sense strongemotion but we may never sense one that will give usthe key to the mystery. It's like having eyes. We maysee, but we may not see the right thing, not ever."

 "Youwill," said Bigman confidently.

 Dropping down toward Jupiter Nine reminded Big­man very strongly of similar maneuvers in the asteroidbelt. As Lucky had explained on the voyage outward,most astronomers considered Jupiter Nine to have beena true asteroid to begin with; a rather large one thathad been captured by Jupiter's tremendous gravity fieldmany millions of years previously.

 In fact, Jupiter had captured so many asteroids thathere, fifteen million miles from the giant planet, therewas a kind of miniature asteroid belt belonging to Jupi­ter alone. The four largest of these asteroid satellites,each from forty to a hundred miles in diameter, were

 29

 30                        

 Jupiter Twelve, Eleven, Eight, and Nine. In addition there were at least a hundred additional satellites of more than a mile in diameter, unnumbered and un­regarded. Their orbits had been plotted only in the lastten years when Jupiter Nine was first put to use as ananti-gravity research center, and the necessity of travel­ing to and from it had made the population of sur­rounding space important.

 The approaching satellite swallowed the sky and be­came a rough world of peaks and rocky channels, un-softened by any touch of air in the billions of years of its history. Bigman, still thoughtful, said, "Lucky, whyin Space do they call this Jupiter Nine, anyway? Itisn't the ninth one out from Jupiter according to theAtlas. Jupiter Twelve is a lot closer."

 Lucky smiled. "The trouble with you, Bigman, is thatyou're spoiled. Just because you were born on Mars,you think mankind has been cutting through space eversince creation. Look boy, it's only a matter of a thou­sand years since mankind invented the first spaceship."

 "I know that," said Bigman indignantly. "I'm notignorant. I've had schooling. Don't go shoving your bigbrain all over the place."

 Lucky's smile expanded, and he rapped Bigman'sskull with two knuckles. "Anybody home?"

 Bigman's fist whipped toward Lucky's abdomen, butLucky caught it in midair and held the little fellowmotionless.

 "If s as simple as this, Bigman. Before space travelwas invented, men were restricted to Earth and all theyknew about Jupiter was what they could see in a tele­scope. The satellites are numbered in the order theywere discovered, see?"

 31

 "Oh," said Bigman, and yanked free. "Poor ances­tors!" He laughed, as he always did, at the thought of human beings cooped up on one world, peering outlongingly, even as he struggled to free himself from Lucky's grip.

 Lucky went on. "The four big satellites of Jupiter arenumbered One, Two, Three, and Four, of course, butthe numbers are hardly ever used. The names Io,Europa, Ganymede, and Callisto are familiar names.The nearest satellite of all, a small one, is Jupiter Five,while the farther ones have numbers up to Twelve. Theones past Twelve weren't discovered till after spacetravel was invented and men had reached Mars and the asteroid belt . . . Watch out now. We've got toadjust for landing."

 It was amazing, thought Lucky, how you could con­sider tiny a world eighty-nine miles in diameter as longas you were nowhere near it. Of course, such a worldis tiny compared to Jupiter or even to Earth. Place itgently on Earth and its diameter is small enough toallow it to fit within the state of Connecticut withoutlapping over; and its surface area is less than that ofPennsylvania.

 And yet, just the same, when you came to enter thesmall world, when you found your ship enclosed in alarge lock and moved by gigantic grapples (workingagainst a gravitational force of almost zero but againstfull inertia) into a large cavern capable of holding ahundred ships the size of theShooting Starr, it no longerseemed so small.

 And then when ,you came across a map of JupiterNine on the wall of an office and studied the network of

 32                        

 underground caverns and corridors within which acomplicated program was being carried out, it beganto seem actually large. Both horizontal and vertical pro­jections of the work volume of Jupiter Nine were shownon the map, and though only a small portion of thesatellite was being used, Lucky could see that some ofthe corridors penetrated as much as two miles beneaththe surface and that others spread out just under thesurface for nearly a hundred miles.

 "A tremendous job," he said softly to the lieutenantat his side.

 Lieutenant Augustus Nevsky nodded briefly. His uni­form was spotless and gleaming. He had a stiff littleblond mustache, and his wide-set blue eyes had a habitof staring straight ahead as though he were at perpetualattention.

 He said with pride, "We're still growing."

 He had introduced himself a quarter of an hourearlier, as Lucky and Bigman had stepped from theship, as the personal guide assigned them by Com­mander Donahue.

 Lucky said with some amusement, "Guide? Orguardian, Lieutenant? You are armed."

 Any trace of feeling was carefully washed out of theother's face. "My arms are regulation for officers onduty, Councilman. You will find you will need a guidehere."

 But he seemed to relax, and there was ordinary hu­man feeling about him as he listened to the visitors' awed praise of the project. He said, "Of course theabsence of any significant gravitational field makes cer­ tain engineering tricks feasible that wouldn't work on

 33

 Earth. Underground corridors require practically nosupport."

 Lucky nodded, then said, "I understand that the firstAgrav ship is about ready for take-off."

 The lieutenant said nothing for a moment. His faceblanked free, again, of emotion or feeling. Then he saidstiffly, "I will show you your quarters first. It can bemost easily reached by Agrav, if I can persuade you touse an Agrav cor—"

 "Hey, Lucky," called Bigman in sudden excitement."Look at this."

 Lucky turned. It was only a half-grown cat, gray assmoke, with the look of solemn sadness that catsusually have, and a back that arched readily againstBigman's curved fingers. She was purring.

 Lucky said, "The commander said they went for petshere. Is this one yours, Lieutenant?"

 The officer flushed. "We all have shares in it. Thereare a few other cats around, too. They come on thesupply ships sometimes. We've got some canaries, aparakeet, white mice, goldfish. Things like that. Noth­ ing like your whatever-it-is, though." And his eyes, as they looked quickly at the V-frog's bowl tucked under Lucky's arm, contained a spark of envy.

 But Bigman was concentrating on the cat There wasno native animal life on Mars and the furry pets ofEarth always had the charm of novelty to him.

 "He likes me, Lucky."

 "It's a she," said the lieutenant, but Bigman paid noattention. The cat, tail hoisted into a stiff vertical withonly the tip drooping, walked past him, doublingsharply so as to present first one side, then the other, to Bigman's gentle stroking.

 34                        

 And then the purring stopped, and through Bigman'smind stabbed one pure touch of fevered and hungrydesire.

 It startled him for a moment, and then he noticed that the cat had stopped purring and was squattingslightly in the tense hunting posture dictated by itsmillions-of-years-old instincts.

 Her green slitted eyes stared directly at the V-frog.But the emotion, so feline in its touch, was gonealmost as soon as it had come. The cat padded softlyover to the glass container Lucky was holding andstared in curiously, purring with contentment.The cat, too, liked the V-frog. It had to.Lucky said, "You were saying, Lieutenant, we wouldhave to reach our quarters by Agrav. Were you going to explain what that means?"

 The lieutenant, who had also been staring fondly atthe V-frog, paused to gather his wits before answering."Yes. It's simple enough. We have artificial gravityfields here on Jupiter Nine as on any asteroid or on anyspace ship for that matter. They are arranged at eachof the main corridors, end to end, so that you can fallthe length of them in either direction. It's like droppingstraight down a hole on Earth."Lucky nodded. "How fast do you drop?""Well, that's the point. Ordinarily, gravity pulls con­stantly and you fall faster and faster..."

 "Which is why I ask my question," interposed Luckydryly.

 "But not under Agrav controls. Agrav is reallyA-grav: no gravity, you see. Agrav can be used toabsorb gravitational energy or store it or transfer it.The point is you only fall so fast, you see, and no faster.

 35

 With a gravitational field in the other direction, too,you can even slow down. An Agrav corridor with twopseudo-grav fields is very simple and it has been usedas a steppingstone to an Agrav ship which works in a single gravitational field. Now Engineers' Quarters,which is where your rooms will be, is only a little overa mile from here and the most direct route is by Cor­ ridor A-2. Ready?"

 "We will be once you explain how we're to workAgrav."

 "That's hardly a problem." Lieutenant Nevsky pre­sented each with a light harness, adjusting them overthe shoulders and at the waist, talking rapidly about the controls.

 And then he said, "If you'll follow me, gentlemen, the corridor is just a few yards in this direction."

 Bigman hesitated at the opening of the corridor.He was not afraid of space in itself, or of drops inthemselves. But all his life he had been used to bridginggaps under Martian gravity or less. This time thepseudo-grav field was at full Earth-normal, and under its influence the corridor was a brilliantly lighted hole,plummeting, apparently, straight downward, even though in actuality (Bigman's mind told him) it paral­leled the satellite's surface closely.

 The lieutenant said, "Now this is the lane for travel in the direction of Engineers' Quarters. If we were toapproach from the other side, 'down' would appear tobe in the other direction. Or we could make 'up' and 'down' change places by appropriate adjustments ofour Agrav controls."

 He looked at the expression on Bigman's face and

 36                        

 said, "You'll get the idea as you go along. It becomessecond nature after a while."

 He stepped into the corridor and didn't drop aninch. It was as though he were standing on an invisible platform.

 He said earnestly, "Have you set the dial at zero?''

 Bigman did so, and instantly all sensation of gravityvanished. He stepped into the corridor.

 Now the lieutenant's hand on the central knob of hisown controls turned it sharply, and he sank, gatheringspeed. Lucky followed him, and Bigman, who wouldsooner have fallen the length of the corridor under double gravity and been smashed to pulp than fail todo anything Lucky did, took a deep breath and lethimself fall.

 "Turn back to zero," called the lieutenant, "andyou'll be moving at constant velocity. Get the feel of it"

 Periodically they approached and passed through luminous green letters that glowedkeep to this side, Once there was the flash of a man passing (falling,really) in the other direction. He was moving much more rapidly than they were.

 "Are there ever any collisions, Lieutenant?" askedLucky.

 "Not really," said the lieutenant. "The experienceddropper watches for people who might be overtaking him or whom he might be overtaking, and it's easyenough to slow down or speed up. Of course the boys will bump on purpose sometimes. It's a kind of rowdyfun that ends with a broken collarbone sometimes."He looked quickly at Lucky. "Our boys play rough."

 Lucky said, "I understand. The commander warnedme."

 37

 Bigman, who had been staring downward throughthe well-lit tunnel into which he was sinking, cried insudden exhilaration, "Hey, Lucky, this is fun when you get used to it," and turned his controls into the positiveregion.

 He sank faster, his head moving down to a level withLucky's feet, then farther down at an increasing rate.

 Lieutenant Nevsky cried out in instant alarm, "Stop that, you fool. Turn back into the negatives!"

 Lucky called out an imperious, "Bigman, slowdown!"

 They caught up to him, the lieutenant angrily ex­claiming. "Don't ever do that! There are all sort of bar­riers and partitions along these corridors, and if youdon't know your way, you'll be slamming into one justwhen you think you're safe."

 "Here, Bigman," said Lucky. "Hold the V-frog. Thatwill give you some responsibility and make you behave,perhaps,"

 "Aw, Lucky," said Bigman, abashed. "I was justkicking my heels a bit. Sands of Mars, Lucky..."

 "All right," said Lucky. "No harm done," and Big­man brightened at once.

 Bigman looked down again. Falling at a constant ratewas not quite the same as free fall in space. In space,nothing seemed to move. A space ship might be travel­ing at a velocity of hundreds of thousands of miles an hour and there would still be the sensation of motion-lessness all about. The distant stars never moved.

 Here, though, the sense of motion was all about. Thelights and openings and various attachments that linedthe corridor walls flashed past.

 In space, one expected that there would be no "up"

 38                        

 and "down," but here there was none either and itseemed wrong. As long as he looked "down" past hisfeet, it seemed "down" and that was all right. When helooked "up," however, there would be a quick sensa­tion that "up" was really "down," that he was standinghead downward falling "up." He looked toward his feetagain quickly to get rid of the sensation.

 The lieutenant said, "Don't bend too far forward,Bigman. The Agrav works to keep you lined up in the direction of fall, but if you bend over too much, you'llstart tumbling."

 Bigman straightened.

 The lieutenant said, "There's nothing fatal abouttumbling. Anyone who's used to Agrav can straightenhimself out again. Beginners would find it troublesome,however. We'll decelerate now. Move the dial into thenegatives and keep it there. About minus five."

 He was slowing as he spoke, moving above them.His feet dangled at Bigman's eye level.

 Bigman moved the dial, trying desperately to linehimself up with the lieutenant. And as he slowed, "up"and "down" became definite, and in the wrong way.Hewas standing on his head.

 He said, "Hey, the blood's rushing to my head."

 The lieutenant said sharply, "There are footholds along the sides of the corridor. Hook one with the toeof your foot as you reach it and let go quickly."

 He did so as he said this. His head swung outward,and head and feet reversed position. He continuedswinging and stopped himself with a quick hand tapagainst the wall.

 Lucky followed suit, and Bigman, flailing widely withhis short legs, managed to catch one of the footholds

 39

 at last. He whirled sharply and caught the wall with hiselbow just a trifle too hard for comfort but managed to line up properly.

 At least he was head-up again. He wasn't falling anymore, but rising, as though he had been shot out of acannon and rising against gravity more and moreslowly; but at least he was head-up.

 When they were moving at a slow crawl, Bigman, looking uneasily toward his feet, thought: We're goingto be falling again. And suddenly the corridor lookedlike an endlessly deep well and his stomach tightened.

 But the lieutenant said, "Adjust to zero," and at once they stopped slowing down. They just moved upward,as though in a smooth, slow elevator, until they reacheda cross-level at which the lieutenant, seizing a footholdwith one toe, brought himself to a feathery stop.

 "Engineers' Quarters, gentlemen," he said.

 "And," added Lucky Starr gently, "a reception com­mittee."

 For men were waiting for them in the corridor now, fifty of them at least.

 Lucky said, "You said they liked to play rough, Lieutenant, and maybe they want to play now."

 He stepped firmly out into the corridor. Bigman,nostrils flaring with excitement and grateful to be on thefirm pseudo-grav of a solid floor, clutched the V-frog'scage tightly and was at Lucky's heels, facing the wait­ing men of Jupiter Nine.

 4

 Initiation!

 Lieutenant Nevsky tried to make his voice crackle withauthority as he placed his hand on the butt of hisblaster. "What are you men doing here?"

 There was a small murmur from the men, but by andlarge they remained quiet. Eyes turned to the one ofthem who stood in front, as though they were waitingfor him to speak.

 The leader of the men was smiling, and his face wascrinkled into an expression of apparent good will. Hisstraight hair, parted in the middle, had a light-orange tint to it. His cheekbones were broad and he chewedgum. His clothing was of synthetic fiber, as was true ofthat of the others, but unlike the others', his shirt andtrousers were ornamented with brass buttons that werelarge and bulky. Four on his shirt front, one each on thetwo shirt pockets, and four down the side of each pantsleg: fourteen altogether. They seemed to serve no pur­pose; to be only for show.

 "All right, Summers," said the lieutenant, turning tothis man, "what are the men doing here?"

 Summers spoke now in a soft, wheedling voice.

 41

 42                        

 "Well, now, Lieutenant, we thought it would be nice tomeet the new man. He'll be seeing a lot of us. He'll beasking questions. Why shouldn't we meet him now?"

 He looked at Lucky Starr as he spoke, and for amoment there was a touch of ice in that glance thatswallowed up all the show of softness.

 The lieutenant said, "You men should be at work."

 "Have a heart, Lieutenant," said Summers, chewingeven more slowly and leisurely. "We'vebeen working. Now we want to say hello."

 The lieutenant was obviously uncertain as to his nextmove. He looked doubtfully at Lucky.

 Lucky said, "Which rooms are to be ours, Lieu­tenant?"

 "Rooms 2A and 2B, sir. To find them—"

 ''I'l find them. I'm sure one of these men will directme. And now, Lieutenant Nevsky, that you've directedus to our quarters, I think your assignment is com­pleted. I'll be seeing you again."

 "I can't leave!" said Lieutenant Nevsky in a low,appalled whisper.

 "I think you can."

 "Sure you can, Lieutenant," said Summers, grinning more broadly than ever. "A simple hello won't hurt theboy." There was a snicker of laughter from the menbehind him. "And besides, you've been asked to leave."

 Bigman approached Lucky and muttered in anurgent whisper. "Lucky, let me give the V-frog to thelieutenant I can't fight and hold it, too."

 "You just hold it," said Lucky. "I want it exactlyhere.... Good day, Lieutenant. Dismissed!"

 The lieutenant hesitated, and Lucky said in a tone

 43

 that, for all its softness, bit like steel. "That's an order,Lieutenant."

 Lieutenant Nevsky's face assumed a soldierly rigid­ity. He said sharply, "Yes, sir."

 Then, surprisingly, he hesitated one further moment and glanced down at the V-frog in the crook of Big-man's arm, as it chewed idly at a fern frond. "Take careof that little thing." He turned and was in the Agravcorridor in two steps, disappearing almost at once ina rush of speed.

 Lucky turned to face the men again. He was underno illusions. They were grim-faced and they meantbusiness, but unless he could face them down and prove that he meant business as well, his mission would cometo nothing against the rock of their hostility. He would have to win them over somehow.

 Summers' smile had become the least bit wolfish. Hesaid, "Well, now, friend, the uniform-boy is gone. Wecan talk. Fm Red Summers. What's your name?"

 Lucky smiled in return. "My name is David Starr.My friend's name is Bigman."

 "Seems to me I heard you called Lucky when all thatwhispering was going on a while back."

 "I'm called Lucky by my friends."

 "Isn't that nice. Do you want to stay lucky?"

 "Do you know a good way?"

 "Matter of fact, Lucky Starr, I do." Suddenly hisface contorted itself into a bitter scowl. "Get off Jupiter Nine."

 There was a hoarse roar of approval from the others,and a few voices took up the cry of "Get off! Get off!"

 44                        

 They crowded closer, but Lucky stood his ground. "I have important reasons to stay on Jupiter Nine."

 "In that case, I'm afraid you aren't lucky," said Sum­mers. "You're a greenhorn and you look soft, and soft greenhorns get hurt on Jupiter Nine. We worry aboutyou."

 "I think I won't get hurt."

 "That's what you think, eh?" said Summers. "Ar-mand, come here."

 From the ranks behind him, a huge man stepped for­ward, round-faced, beefy of build, with large shouldersand a barrel chest. He topped Lucky's six feet one byhalf a head and looked down at the young councilmanwith a smile that showed yellowed, wide-spaced teeth.

 The men were beginning to take seats on the floor.They shouted to one another with lighthearted cheer, as though they were about to watch a ball game.

 One called out, "Hey, Armand, watch out you don'tstep on the kid!"

 Bigman started, and glared furiously in the directionof the voice but could not identify the speaker.

 Summers said, "You could still leave, Starr."

 Lucky said, "I have no intention of doing so, particu­larly at a moment when you seem to be planning somesort of entertainment."

 "Not for you," said Summers. "Now listen, Starr, we're ready for you. We've been ready since we gotword that you were coming. We've had enough of youlittle tinhorns from Earth and we aren't taking any more. I've got men stationed on various levels. We'llknow if the commander tries to interfere, and if he does, then by Jupiter, we're ready to go on strike. Am I right, men?"

 45

 "Right!"came back the multiple roar.

 "And the commander knows it," said Summers, "andI don't think he'll interfere. So this gives us our chanceto give you our initiation and after that I'll ask youagain if you want to leave. If you're conscious, that is."

 "You're going to a lot of trouble for nothing," saidLucky. "What harm am I doing you?"

 "You won't be doing us any," said Summers. "I guar­antee that."

 Bigman said, in his tense, high-pitched voice, "Look,you cobber, you're talking to a councilman. Have you stopped to figure what happens if you fool with theCouncil of Science?"

 Summers looked at him suddenly, put his fists on hiships, and bent his head back to laugh. "Hey, men, ittalks. I was wondering what it was. It looks as thoughLucky Snoop has brought along his baby brother for protection."

 Bigman went dead-white, but under the cover of thelaughter Lucky stooped and spoke through stiff lips."Your job is to hang on to the V-frog, Bigman. I'll takecare of Summers. And, Great Galaxy, Bigman, stopbroadcasting anger! I can't get a thing on the V-frogexcept that."

 Bigman swallowed hard twice, three tunes.

 Summers said softly, "Now, Councilman Snoop, canyou maneuver under Agrav?"

 "I just have, Mr. Summers."

 "Well, we'll just have to test you and make sure.We can't have anyone around who hasn't learned allthe Agrav ropes. It's too dangerous. Right, men?"

 "Right!" they roared again.

 "Armand here," said Summers, and his hand rested

 46                        

 on one of Armand's huge shoulders, "is our bestteacher. You'll know all about Agrav maneuvering when you're through with him. Or you will know ifyou stay out of his way. I suggest you get out into theAgrav corridor now. Armand will join you."

 Lucky said, "If I choose not to go?"

 "Then we'll throw you into the corridor anyway andArmand goes after you."

 Lucky nodded. "You seem determined. Are there any rules to this lesson I'm going to get?"

 There was wild laughter, but Summers held up hisarms. "Just keep out of Armand's way, Councilman.That' s the only rule you'll have to remember. We'll beat the lip of the corridor watching. If you try to crawlout of Agrav before you've completed your lesson, we'llthrow you back in, and there are men stationed at otherlevels, watching, and they're ready to do the same."

 Bigman cried, "Sands of Mars, your man outweighs Lucky by fifty pounds and he's an expert with Agrav!"

 Summers turned on him in mock surprise."No! Inever thought of that. What a shame!" There waslaughter from the men. "On your way, Starr. Get intothe corridor, Armand. Drag him in if you have to."

 "He won't have to," said Lucky. He turned andmoved into the open space of the wide Agrav corridor.As his feet drifted out into empty air, his fingers caughtgently at the wall, twisting him in a slow, turning mo­tion that he stopped with another touch against thewall. He stood there in midair, facing the men.

 There was some murmuring at Lucky's maneuver,and Armand nodded, speaking for the first time in arolling appreciative bass. "Hey, mister, that's not bad."

 Summers, lips suddenly set and with a frown newly

 47

 creasing his forehead, struck Armand a sharp blow onthe back. "Don't talk, you idiot! Get in after him andgive it to him."

 Armand moved forward slowly. He said, "Hey, Red,let's not make too much of this."

 Summers' face contorted in fury. "Get in there! Andyou do what I said. I told you what he is. If we don'tget rid of him, they'll be sending more." His words werea harsh whisper that didn't carry.

 Armand stepped into the corridor and stood face toface with Lucky.

 Lucky Starr waited in what was almost absence ofmind. He was concentrating on the faint whiffs of emo­tion brought him by the V-frog. Some he could recog­nize without difficulty, both as to their nature and theirowner. Red Summers was easiest to detect: fear and niggling hate mixed with an undertone of anxious tri­umph. Armand loosed a small leak of tension. Occa­sionally there were sharp pinpoints of excitement fromone or another, and sometimes Lucky could identify theowner because it coincided with a happy shout or a threatening one. All of it had to be sorted out from the steady trickle of Bigman's anger, of course.

 But now he was staring into Armand's small eyes andhe was aware that the other was bobbing up and down,a few inches either way. Armand's hand fingered hischest control.

 Lucky was instantly alert. The other was alternatingthe gravitational direction, moving the controls this way and that. Was he expecting to confuse Lucky?

 Lucky was sharply aware that for all his experiencewith space he was inexperienced in the type of weight-

 48                        

 lessness brought about by Agrav, for this was a weight­lessness that wasn't absolute, as in space, but one that could be changed at will.

 And suddenly Armand dropped as though he hadstepped through a trap door—except that he droppedupward!

 As Armand's large legs moved up past Lucky's head,they parted and came together as if to catch Lucky's head in a vise.

 Automatically Lucky's head snapped back, but as itdid so, his legs moved forward, his body swinging aboutits center of gravity, and for a moment, he was off bal­ ance and flailing helplessly. A roar of laughter arosefrom the watching men.

 Lucky knew what was wrong. He should havedodged by gravity. If Armand moved up, Lucky shouldhave adjusted controls to move up with him or to racedown past him. And now it would take the pull of grav­ity to straighten him out. At gravity zero, he wouldtumble indefinitely.

 But before bis fingers could touch his controls, Ar­mand was past the top of his rise and was gatheringspeed downward. As he dropped past Lucky oncemore, his elbow caught Lucky a sharp jab in the hip. He dropped farther and his thick fingers clutched at Lucky's ankles, carrying him down, down. Armandpulled strongly downward and reached up to seizeLucky's shoulders. His harsh breath stirred Lucky's hair. He said, "You need a lot of training, mister."

 Lucky brought up his own arms head-high and brokethe other's hold sharply.

 Lucky dialed gravity up and helped Ms upwardmovement by bringing his foot sharply down on the

 49

 other's shoulder, accelerating Ms own pace and slowingthe other's. To his own senses it now seemed that hewas falling head downward and there was a tensenessabout that sensation that seemed to be slowing hisreactions. Or was it his Agrav controls which were somewhat sluggish? He tested them and lacked theexperience to be certain, yet felt that they were.

 Armand was on him now, bellowing, thrustingagainst him, attempting to use his own greater mass ofbody to maneuver Lucky hard against the wall.

 Lucky wriggled his hand toward the controls in order to reverse the direction of gravity. He readied his kneesfor an upward thrust to coincide and lurch Armand outof position.

 But it was Annand's field that shifted first, and itwas Lucky who was lurched out of position.

 Annand's feet shot backward now, striking the wallof the corridor as it was flashing by and angling thepair, by recoil, against the opposite wall. Lucky struck bruisingly and skidded along it some feet before hisankle caught one of the metal railings and his bodyswung away and into the open corridor.

 Armand whispered hotly in Lucky's ear, "Hadenough, mister? Just tell Red you'll leave. I don't wantto hurt you bad."

 Lucky shook his head. Strange, he thought, that Ar-mand's gravitational field had beaten his own to theshift. He had felt Armand's hand move to the controlsand he was certain his own controls had moved first.

 Twisting suddenly, Lucky placed his elbow sharplyin the pit of Armand's stomach. Armand grunted, andin that split second Lucky got his legs between himself

 50                        

 and the other's and straightened them. The two menflew apart and Lucky was free.

 He shot away an instant before Armand returned,and then for the next few minutes Lucky concentrated only on staying away. He was learning the use of thecontrols and theywere sluggish. It was only by skillful use of the footholds along the walls and lightning-likehead-to-foot reversals that he managed to avoid Ar­mand.

 And then while he was drifting feather-fashion,allowing Armand to shoot past him, he turned his Agrav controls and found no response at all. Therewas no change in the gravitational field direction; nosudden sensation of accelerating one way or the other.

 Instead, Armand was on him again, grunting, andLucky found himself crashing with stunning force against the corridor wall.

 5

 Needle-Guns and Neighbors

 Bigman felt fully confident of Lucky's ability to handleany overgrown mass of beef, and though he felt a sharpanger at the unsympathetic crowd, he felt no fear.

 Summers had approached the lip of the corridor andso had another, a gangling, dark-complexioned fellowwho barked out events as they occurred in a raucousvoice, as though it were a flight-polo game on thesubetherics.

 There were cheers when Armand first slammedLucky against the corridor wall. Bigman discountedthose with contempt. Of course that shouting fool would try to make it look good for his own side. Waittill Lucky got the feel of the Agrav technique; he wouldcut that Armand guy into ribbons. Bigman was sureof it.

 But then when the dark fellow yelled, "Armand hashim now in a head lock. He's maneuvering for asecond fall; feet against the wall; retract and extendandthere's the crash, a beauty!" Bigman felt the begin­nings of uneasiness.

 He edged close to the corridor himself. No one paid

 51

 52                        

 any attention to him. It was one advantage of his smallsize. People who didn't know him tended to discounthim as a possible danger, to ignore him.

 Bigman looked down and saw Lucky pushing awayfrom the wall, Armand drifting nearby, waiting.

 "Lucky!" he yelled shrilly. "Stay away!"

 His cry was lost in the hubbub, but the dark man'svoice as it was lowered in a conversational aside to RedSummers was not. Bigman caught it.

 The dark man said, "Give the snoop some power,Red. There won't be any excitement."

 And Summers growled in response, "I don't wantexcitement. I want Armand to finish the job."

 Bigman didn't get the significance of the short ex­change for a moment, but only for a moment. Andthen his eyes darted sharply in the direction of RedSummers, whose hands, held closely against his chest,were manipulating some small object Bigman couldnot identify.

 "Sands of Mars!" Bigman cried breathlessly. Hesprang back. "You! Summers! You foul-fighting cob­ber!"

 This was another one of those tunes when Bigmanwas glad he carried a needle-gun even in the face ofLucky's disapproval. Lucky considered it an unreliableweapon, as it was too hard to focus accurately, but Big­man would sooner doubt the fact that he was as tall asany six-footer as doubt his own skill.

 When Summers didn't turn at Bigman's shout, Big­man clenched his fist about the weapon (of which only half-inch of snout, narrowing to a needlepoint, showed between the second and third fingers of his right hand)and squeezed just tightly enough to activate it.

 53

 Simultaneously there was a flash of light six inchesin front of Summers' nose, and a slight pop. It was notvery impressive. Only air molecules were being ionized.Summers jumped, however, and panic, transmitted bythe V-frog, rose sharply.

 "Everybody," called Bigman. "Freeze!Freeze! You split-head, underlipped miseries." Another needle-gundischarge popped the air, this time over Summers' headwhere all could see it plainly.

 Few people might have handled needle-guns, which were expensive and hard to get licenses for, but every­body knew what a needle-gun discharge looked like, ifonly from subetheric programs, and everyone knew thedamage it could do.

 It was as though fifty men had stopped breathing.Bigman was bathed in the cold drizzle of human fearfrom fifty frightened men. He backed against the wall.He said, "Now listen, all of you. How many of youknow that this cobber Summers is gimmicking my friend's Agrav controls? This fight is fixed!"

 Summers said desperately, through clenched teeth,"You're wrong. You're wrong."

 "Am I? You're a brave man, Summers, when you'vegot fifty against two. Let's see you stay brave against aneedle-gun. They're hard to aim, of course, and I mightmiss."

 He clenched his fist again, and this time the pop of the discharge was sharply ear-splitting and the flashdazzled all the spectators but Bigman, who, of them all, was the only one who knew exactly when to close his eyes for a moment.

 Summers emitted a strangled yell. He was untouchedexcept that the top button on his shirt was gone.

 54                        

 Bigman said, "Nice aiming if I do say so myself, butI suppose having a run of luck is too much to ask. I'dadvise you not to move, Summers. Pretend you're stone,you cobber, because if you do move, I'll miss and feel­ ing a chunk of your skin go will hurt you worse thanjust losing a button."

 Summers closed his eyes. His forehead was glisteningwith perspiration. Bigman calculated the distance andclenched twice.

 Pow! Smack! Two more buttons gone.

 "Sands of Mars, my lucky day! Isn't it nice thatyou've arranged to have no one come around to inter­fere? Well, one more—for the road."

 And this tune Summers yelled in agony. There was arent in the shirt and reddened skin showed.

 "Aw," said Bigman, "not on the nose. Now I'm rattled and I'll probably miss the next by two inches... Unless you're ready to say something, Summers."

 "All right," yelled the other. ''I've fixed it."

 Bigman said mildly, "Your man was heavier. Yourman had experience and still you couldn't leave it afair fight. You don't takeany chances, do you? Dropwhat you're holding . . . Don't the rest of you move,though. From here on in, it's a fair fight in the corridor.No one's moving until someone climbs out of the corridor."

 He paused and glared as his fist with the needle-gunmoved slowly from side to side."But if it's your ball ofgristle that comes back, I'll just be a bit disappointed.And when I'm disappointed, there's no telling what I'lldo. I just might be disappointed and mad enough tofire this needle-gun into the crowd, and there isn't a thing in the world any of you can do to stop me from

 55

 clenching my fist ten times. So if there are ten of you bored with living, just hope that your boy beats LuckyStarr."

 Bigman waited there desperately, his right hand holding the needle-gun, his left arm crooked over theV-frog in its container. He longed to order Summers tobring the two men back, to end the fight, but he darednot risk Lucky's anger. He knew Lucky well enough toknow that the fight couldn't be allowed to end bydefault on Lucky's side.

 A figure whizzed past the line of sight, then another.There was a crash as of a body hitting a wall, then asecond and a third. Then silence.

 A figure drifted back, with a second gripped firmly by one ankle.

 The person in control came lightly out into the cor­ridor; the person being held followed and dropped likea sack of sand.

 Bigman let out a shout. The man standing wasLucky. His cheek was bruised and he limped, but itwas Armand who was unconscious.

 They brought Armand back to consciousness withsome difficulty. He had a lump on his skull resemblinga small grapefruit, and one eye was swollen closed.Though his lower lip was bleeding, he managed a pain­ ful smile and said, "By Jupiter, this kid's a wildcat."

 He got to his feet and threw his arms about Luckyin a bear hug. "It was like tangling with ten men afterhe got his bearings. He's all right."

 Surprisingly, the men were cheering wildly. TheV-frog transmitted relief first, swallowed up at once byexcitement.

 56                        

 Armand's smile widened, and he dabbed at the blood with the back of his hand. "This councilman is all right.Anyone who still doesn't like him has to fight me, too. Where's Red?"

 But Red Summers was gone. So was the instrumenthe had dropped at Bigman's order.

 Annand said, "Listen, Mr. Starr, I've got to tell you.This wasn't my idea, but Red said we had to get ridof you or you'd make trouble for all of us."

 Lucky raised his hand. "That's a mistake. Listen, allof you. There'll be no trouble for any loyal Earthman.I guarantee it. This fight is off the record. It was a bitof excitement, but we can forget it. Next time we meet,we all meet fresh. Nothing's happened. Right?"

 They cheered madly and there were shouts of "He'sall right" and "Up the Council!"

 Lucky was turning to go when Armand said, "Hey,wait." He drew in a vast breath and pointed a thick finger. "What's this?" He was pointing to the V-frog.

 "A Venusian animal," said Lucky. "A pet of ours."

 "It's cute." The giant simpered down at it. Theothers crowded close to stare at it and make apprecia­tive comments, to seize Lucky's hand and assure himthat they had been on his side all along.

 Bigman, outraged at the shoving, finally yelled,"Let's get to quarters, Lucky, or I swear I'll kill a fewof these guys."

 There was an instant silence and men squeezedback to make a path for Lucky and Bigman.

 Lucky winced as Bigman applied cold water to thebruised cheek in the privacy of their quarters.

                                                                                57

 He said, "Some of the men were saying somethingabout needle-guns in that final crush, but in the con­fusion I didn't get the story straight. Suppose you tellme, Bigman."

 Reluctantly Bigman explained the circumstances.

 Lucky said thoughtfully, "I realized that my controlswere off, but I assumed mechanical failure particularlysince they came back after my second fall. I didn'tknow you and Red Summers were fighting it out over me."

 Bigman grinned. "Space, Lucky, you didn't think I'dlet that character pull a trick like that?"

 "There might have been some way other than needle-guns."

 "Nothing else would have frozen them so," said Big­man, aggrieved. "Did you want me to shake my finger at them and say, 'Naughty, naughty?' Besides, Ihad toscare the green bejeebies out of them."

 "Why?" Lucky said sharply.

 "Sands of Mars, Lucky, you spotted the other guytwo falls when the fighting was fixed, and I didn't know if you had enough left to make out. I was going to makeSummers call the fight off."

 "That would have been bad, Bigman. We wouldhave gained nothing. There would have been men con­vinced the cry of 'foul' was an unsportsmanlike fake."

 "I knew you'd figure that, but I was nervous."

 "No need to be. After my controls started respondingproperly, things went fairly well. Armand was certainhe had me, and when he found there was still fight inme, the fight seemed to go out of him. That happenssometimes with people who have never had to lose.

 58                        

 When they don't win at once, it confuses them, and they don't win at all."

 "Yes, Lucky," said Bigman, grinning.

 Lucky was silent for a minute or two, then he said,"I don't like that 'Yes, Lucky.' What did you do?"

 "Well—" Bigman applied the final touch of fleshtint to hide the bruise and stepped back to consider hishandiwork critically—"I couldn't help but hope thatyou'd win, now could I?"

 "No, I suppose not."

 "And I told everyone in that place that if Armandwon, I would shoot as many of them as I could."

 "You weren't serious."

 "Maybe I was. Anyway, they thought I was; theywere sure I was after they saw me needle four buttons off that cobber's shirt. So there were fifty guys there,even including Summers, who were sweating themselvesblind hoping you would win and Armand lose."

 Lucky said, "So that's it."

 "Well, I couldn't help it if the V-frog was there andtransmitted all those thoughts to you too, could I?"

 "So all the fight went out of Armand because hismind was blanketed with wishes he would lose." Luckylooked chagrined.

 "Remember, Lucky. Two foul falls. It wasn't a fairfight."

 "Yes, I know. Well, maybe I needed the help at that."

 The door signal flashed at that moment, and Luckyraised his eyebrows. "Who's this, I wonder?" He pressedthe button that retracted the door into its slot.

 A chunky man, with thinning hair and china-blue

                                                                                59

 eyes that stared at them unblinkingly, stood in the door­way. In one hand he held an oddly shaped piece ofgleaming metal, which his limber fingers turned endfor end. Occasionally the piece ducked between fingers,traveling from thumb to pinkie and back as though ithad a life of its own. Bigman found himself watching it,fascinated.

 The man said, "My name is Harry Norrich. I'm yournext-door neighbor."

 "Good day," said Lucky.

 "You're Lucky Starr and Bigman Jones, aren't you?Would you care to come to my place a few minutes? Visit a bit, have a drink?"

 "That's kind of you," said Lucky. "We'll be glad tojoin you."

 Norrich turned somewhat stiffly and led the waydown the corridor to the next door. One hand touched the corridor wall occasionally. Lucky and Bigman fol­lowed, the latter holding the V-frog.

 "Won't you come in, gentlemen?" He stood aside to let them enter. "Please sit down. I've heard a great dealabout you already."

 "Like what?" asked Bigman.

 "Like Lucky's fight with Big Armand and Bigman'smarksmanship with a needle-gun. It's all over the place.I doubt there's anyone on Jupiter Nine who won't hear of it by morning. It's one of the reasons I asked you in.I wanted to talk to you about it."

 He poured a reddish liquor carefully into two smallglasses and offered them. For a moment Lucky put his hand some three inches to one side of the glass, waitedwithout result, then reached over and took it fromNorrich's hand. Lucky put the drink to one side.

 60                        

 "What's that on your worktable?" asked Bigman.

 Norrich's room, in addition to the usual furnishings,had something that looked like a worktable running the length of one wall with a bench before it. On the work-table was a series of metal gimmicks spread out loosely,and in the center was an odd structure, six inches highand very uneven hi outline.

 "This thing?" Norrich's hand slid delicately along thesurface of the table and came to rest on the structure."It's a threedee."

 "A what?"

 "A three-dimensional jigsaw. The Japanese had themfor thousands of years, but they've never caught on else­where. They're puzzles, made up of a number of piecesthat fit together to form some sort of structure. Thisone, for instance, will be the model of an Agrav genera­tor when it's finished. I designed and made this puzzlemyself."

 He lifted the piece of metal he was holding andplaced it carefully in a little slot in the structure. Thepiece slid in smoothly and held in place.

 "Now you take another piece." His left hand movedgently over the structure, while his right felt among theloose pieces, came up with one, and moved it intoplace.

 Bigman, fascinated, moved forward, then jumped back at a sudden animal howl from beneath the table.

 A dog came squirming out from beneath the tableand put its forefeet on the bench. It was a large Germanshepherd dog and it stood now looking mildly atBigman.

 Bigman said nervously, "Here, now, I stepped onit by accident."

                                                                                61

 "It's only Mutt," said Norrich. "He won't hurt any­one without better cause than being stepped on. He's my dog. He's my eyes."

 "Your eyes?"

 Lucky said softly, "Mr. Norrich is blind, Bigman."

  

 6

 Death Enters the Game

 Bigman shrank back. "I'm sorry."

 "No need to be sorry," Norrich said cheerfully. "I'mused to it and I can get along. I'm holding a mastertechnician's rank and I'm in charge of constructing ex­perimental jigs. I don't need anyone to help me, either,any more than I need help in my threedees."

 "I imagine the threedees offer good exercise," saidLucky.

 Bigman said, "You mean you can put those thingstogether without even being able to see them? Sandsof Mars!"

 "It's not as hard as you might think. I've been prac­ticing for years and I make them myself so I know thetricks of them. Here, Bigman, here's a simple one. It'sjust an egg shape. Can you take it apart?"

 Bigman received the light-alloy ovoid and turned itin his hands, looking over the pieces that fit togethersmoothly and neatly.

 "In fact," Norrich went on, "the only thing I reallyneed Mutt for is to take me along the corridors." Heleaned down to scratch the dog behind one ear, and

 63

 64                        

 the dog permitted it, opening his mouth wide in a sleepyyawn, showing large white fangs and a length of pinklolling tongue. Lucky could feel the warm thickness of Norrich's affection for the dog pour out via the V-frog.

 "I can't use the Agrav corridors," Norrich said,"since I'd have no way of telling when to decelerate,so I have to walk through ordinary corridors and Muttguides me. It makes for the long way around, but it'sgood exercise, and with all the walking Mutt and Iknow Jupiter Nine better than anybody, don't we,Mutt? ... Have you got it yet, Bigman?"

 "No," said Bigman. "It's all one piece."

 "Not really. Here, give it to me."

 Bigman handed it over, and Norrich's skinful fingersflew over the surface. "See this little square bit here?You push it and it goes in a bit. Grab the part that comes out the other end, give it half a turn clockwise, and it pulls out altogether. See? Now the rest coniesapart easily. This, then this, then this, and so on. Lin© up the pieces in order as they come out; there are onlyeight of them; then put them back in reverse order.Put the key piece in last, and it will lock everything intoplace."

 Bigman stared dubiously at the individual pieces andbent close over them.

 Lucky said, "I believe you wanted to discuss thereception committee I met up with when I arrived, Mr. Norrich. You said you wanted to talk about my fightwith Armand."

 "Yes, Councilman, yes. I wanted you to understand. I've been here on Jupiter Nine since Agrav project started and I know the men. Some leave when theirhitch is up, some stay on, greenhorns join up; but

                                                                                65

 they're all the same in one way. They're very insecure."

 "Why?"

 "For several reasons. In the first place, there isdanger involved in the project. We've had dozens ofaccidents and lost hundreds of men. I lost my eyes fiveyears ago and I was fortunate in a way. I might havedied. Secondly, the men are isolated from friends and family while they're here. Really isolated."

 Lucky said, "I imagine there are some people whoenjoy the isolation."

 He smiled grimly as he said that. It was no secret thatmen who in one way or another had gotten entangledwith the law sometimes managed to find work on someof the pioneer worlds. People were always needed towork under domes in artificial atmospheres with pseu-do-grav fields, and those who volunteered were usuallynot asked too many questions. Nor was there anythingvery wrong with that. Such volunteers aided Earth andits people under difficult conditions, and that, in a way,was a payment for misdeeds.

 Norrich nodded at Lucky's words. "I see you're notnaive about it and I'm glad. Leaving the officers andthe professional engineers to one side, I imagine a goodhalf of the men here have criminal records on Earth,and most of the rest might have such records if the po­lice knew everything. I doubt that one in five gives his real name. Anyway, you see where tension comes inwhen investigator after investigator arrives. You're alllooking for Sirian spies; we know that; but each manthinks that maybe his own particular trouble will comeout and he'll be dragged back to jail on Earth. They allwant to go back to Earth, but they want to go backanonymously, not at the other end of a set of wrist

 66                         

 locks. That's why Red Summers could rouse them so."

 "And is Summers something special that he takes thelead? A particularly bad record on Earth?"

 Bigman looked up briefly from his threedee to saybitterly, "Murder, maybe?"

 "No," said Norrich with instant energy. "You've got to understand about Summers. He's had an unfortunatelife: broken home, no real parents. He got into thewrong crowds. He's been in prison, yes, for being in­volved in some minor rackets. If he'd stayed on Earth,his life would have been one long waste. But he's cometo Jupiter Nine. He's made a new life here. He cameout as a common laborer and he educated himself. He's learned low-grav construction engineering, force-fieldmechanics, and Agrav techniques. He's been promotedto a responsible position and has done wonderful work.He's respectable, admired, well liked. He's found out what it is to have honor and position and he dreadsnothing more than the thought of going back to Earthand his old life."

 "Sure, he hates it so much," said Bigman, "that he tried to kill Lucky by gimmicking the fight."

 "Yes," said Norrich, frowning, "I heard he wasusing a sub-phase oscillator to kill the councilman'scontrol response. That was stupid of him, but he was inpanic. Look, fundamentally the man is goodhearted.When my old Mutt died—"

 "Your old Mutt?" asked Lucky.

 "I had a Seeing Eye dog before this one which I alsocalled Mutt. It died in a force-field short circuit thatkilled two men besides. He shouldn't have been there,but sometimes a dog will wander off on his own adven­tures. This one does, too, when I'm not using him,

                                                                                 67

 but he always comes back." He leaned down to slaphis dog's flank lightly, and Mutt closed one eye and thumped his tail against the floor.

 "Anyway, after old Mutt died, it looked for a whileas though I mightn't get another and I would have tobe sent home. I'm no use here without one. Seeing Eyedogs are in short supply; there are waiting lists. Theadministration here at Jupiter Nine didn't want to pullany strings because they weren't anxious to publicize the fact that they were employing a blind man as con­struction engineer. The economy bloc in Congress is always waiting for something like that to make badpublicity out of. So it was Summers who came through.He used some contacts he had on Earth and got meMutt here. It wasn't exactly legal, it was even what youmight call the black market, but Summers risked hisposition here to do a friend a favor and I owe him agreat deal. I'm hoping you'll remember Summers cando and has done things like that and that you'll go easyon him for his actions earlier today."

 Lucky said, "I'm not taking any action against him.I had no intention of doing so even before our conver­sation. Still, I'm sure that Summers' real name andrecord are known to the Council and I'll be checkingon the facts."

 Norrich flushed, "By all means, do so. You'll findhe's not so bad."

 "I hope so. But tell me something. Through all thathas just taken place, there was no attempt on the partof the project administration to interfere. Do you findthis strange?"

 Norrich laughed shortly. "Not at all. I don't thinkCommander Donahue would have cared much if you'd

 68                        

 been killed, except for the trouble it would have takento hush it up. He's got bigger troubles on his mind than you or your investigation."

 "Bigger troubles?"

 "Sure. The head of this project is changed every year;army policy of rotation. Donahue is the sixth boss we'vehad and far and away the best. I've got to say that. He'scut through red tape and he hasn't tried to make anarmy camp out of the project. He's given the men lee­way and let them raise a bit of cain now and then so he's gotten results. Now the first Agrav ship will beready to take off any time. Some say it's a matter ofdays."

 "That soon?"

 "Could be. But the point is that Commander Dona­hue is due to be relieved in less than a month. A delay now could mean that the launching of the Agrav shipwon't take place until Donahue's successor comes in.Donahue's successor would get to ride in it, have thefame, go down in the history books, and Donahuewould miss out."

 "No wonder he didn't want you on Jupiter Nine,"Bigman said hotly. "No wonder he didn't want you,Lucky."

 Lucky shrugged. "Don't waste temper, Bigman."

 But Bigman said, "The dirty cobber! Sirius can gob­ble up Earth for all he cares as long as he can get toride his miserable ship." He lifted a clenched fist, andthere was a muted growl from Mutt.

 Norrich said sharply, "What are you doing, Big­man?"

 "What?" Bigman was genuinely astonished. "I'm notdoing a thing."

                                                                                 69

 "Are you making a threatening gesture?"

 Bigman lowered his arm quickly. "Not really."

 "You've got to be careful around Mutt. He's beentrained to take care of me. . . . Look, I'll show you.Just step toward me and make believe you're going tothrow a punch at me."

 Lucky said, "That's not necessary. We under­stand—"

 "Please," said Norrich. "There's no danger. I'll stop Mutt in time. As a matter of fact, it's good practice forhim. Everyone on the project is so careful of me thatI swear I don't know if he remembers his training. Go ahead, Bigman."

 Bigman stepped forward and raised his arm half­heartedly. At once Mutt's ears flattened, his eyes slitted, his fangs stood sharply revealed, his leg muscles tensed for a spring, and a harsh growl issued from the recessesof his throat.

 Bigman drew back hastily, and Norrich said, "Down,Mutt!" The dog subsided. Lucky could sense, clearly,the gathering and relaxation of tension in Bigman'smind and the fond triumph in Norrich's.

 Norrish said, "How are you doing with the threedeeegg, Bigman?"

 The little Martian, in exasperation, said, "I've givenup. I've got two pieces put together and that's all Ican do."

 Norrich laughed. "Just a matter of practice, that'sall. Look."

 He took the two pieces out of Bigman's hand andsaid, "No wonder. You've got these together wrong.He flipped one piece end for end, brought the two to­gether again, added another piece and another until he

 70                         

 held seven pieces in the shape of a loose ovoid with ahole through it. He picked up the eighth and key piece,slipped it in, gave it a half turn counterclockwise,pushed it the rest of the way, and said, "Finished."

 He tossed the completed egg into the air and caughtit, while Bigman watched in chagrin.

 Lucky got to his feet. "Well, Mr. Norrich, we'll beseeing you again. I'll remember your remarks aboutSummers and the rest. Thank you for the drink." Itstill rested untouched on the desk.

 "Nice to have met you," said Norrich, rising andshaking hands.

 It was some time before Lucky could fall asleep. Helay in the darkness of his room hundreds of feet belowthe surface of Jupiter Nine, listening to Bigman's softsnoring in the adjoining room, and thought of theevents of the day. Over and over them he went.

 He was bothered! Something had happened thatshouldn't have; or something had not happened thatshould have.

 But he was weary and everything was a bit unreal andtwisted in the half-world of half-sleep. Something hov­ered at the edge of awareness. He clutched at it, but itslipped away.

 And when morning came there was nothing left of it.

 Bigman called out to Lucky from his own room asLucky was drying himself under the soft jets of warmair after his shower.

 The little Martian yelled, "Hey, Lucky, I've re­charged the V-frog's carbon-dioxide supply and dumpedin more weed. You'll be taking it down to our meetingwith that blasted commander, won't you?"

                                                                                 71

 "We certainly will, Bigman."

 "It's all set then. How about letting me tell the com­mander what I think of him?"

 "Now, Bigman."

 "Nuts! It's me for the shower now."

 Like all men of the solar system brought up onplanets other than Earth, Bigman reveled in water when he could get at it, and a shower for him was a leisurely,loving experience. Lucky braced himself for a sessionof the tenor caterwauling that Bigman called singing.

 The intercom sounded after Bigman was welllaunched into some dubious fragment of melody thatsounded piercingly off-key and just as Lucky completeddressing.

 Lucky stepped to it and activated reception. "Starrspeaking."

 "Starr!" Commander Donahue's lined face showedin the visi-panel. His lips were narrow and compressed and his whole expression was one of antagonism as hegazed at Lucky. "I have heard some story of a fightbetween yourself and one of our workers."

 "Yes?"

 "I see you have not been hurt."

 Lucky smiled. "All's well."

 "You'll remember I warned you."

 "I am making no complaints."

 "Since you aren't, and in the interest of the project,I would like to ask if you plan making any report con­cerning it."

 "Unless it turns out to have some direct bearing onthe problem which concerns me here, the incident willnever be mentioned by me."

 "Good!" Donahue looked suddenly relieved. "I won-

 72                         

 der if I could extend that attitude to our meeting thismorning. Our meeting might be taped for confidentialrecords and I would prefer—"

 "There will be no need to discuss the matter, Com­mander."

 "Very good!" The commander relaxed into what wasalmost cordiality. "I'll be seeing you in an hour then."

 Lucky was dimly aware that Bigman's shower hadstopped and that his singing had subsided to a hum­ming. Now the humming stopped, too, and there wasa moment of silence.

 Lucky said into the transmitter, "Yes, Commander,good—" when Bigman exploded into a wild, near-incoherent shout,

 "Lucky!"

 Lucky was on his feet with smooth speed and at thedoor connecting the two rooms in two strides.

 But Bigman was in the doorway before him, eyes bigwith horror. "Lucky! The V-frog! It's dead! It's beenkilled!"

 7

 A Robot Enters the Game

 The V-frog's plastic cage was shattered and shriveled,and the floor was wet with its watery contents. TheV-frog, half covered with the fronds it fed upon, wasquite, quite dead.

 Now that it was dead and unable to control emotion,Lucky could look at it without the enforced fondnessthat he, as well as all others that came within its radius of influence, had felt. He felt anger, however—mostlyat himself for having allowed himself to be over­reached.

 Bigman, fresh from his shower, with only his shortson, clenched and unclenched his fists. "It's my fault,Lucky. It's all my fault. I was yelling so loud in theshower I never heard anyone come in."

 The phrase "come in" was not quite appropriate.The killer had not simply come in; he had burnt hisway in. The lock controls were fused and melted awaywith what had obviously been an energy projector offairly large caliber.

 Lucky stepped back to the interphone. "CommanderDonahue?"

 73

 74                         

 "Yes, what happened? Is anything wrong?""I'll see you in an hour." He broke connections andreturned to the grieving Bigman. He said somberly,"It's my fault, Bigman. Uncle Hector said the Sirians had not yet discovered the facts concerning the emo­tional powers of the V-frog, and I accepted that toothoroughly. If I had been a little less optimistic aboutSirian ignorance, neither one of us would ever have leftthat little creature out of our sight for a second."

 Lieutenant Nevsky called for them, standing atattention as Lucky and Bigman left their quarters.

 He said in a low voice, "I am glad, sir, that you wereunharmed in yesterday's encounter. I would not haveleft you, sir, had you not strictly ordered me to."

 "Forget it, Lieutenant," Lucky said absently. Hismind kept returning to that moment just before sleepthe preceding night when, for a brief instant, a thought had hovered at the outskirts of consciousness, thenvanished. But it would not come now, and finallyLucky's mind sped to other matters.

 They had entered the Agrav corridor now, and thistime it seemed crowded with men, streaming accuratelyand unconcernedly in both directions. There was a "beginning of the work day" atmosphere all about. Though men worked underground here and there was no day or night, yet the old twenty-four-hour scheduleheld. Mankind brought the familiar rotation of theEarth to all the worlds on which he lived. And thoughmen might work in shifts the clock round, the largestnumber always worked on the "day shift" from nine to five, Solar Standard Time.

 It was nearly nine now, and there was a bustle

                                                                                75

 through the Agrav corridors as men traveled to thework posts. There was a feel of "morning" almost asstrong as though there were a sun low in the easternsky and dew on the grass.

 Two men were sitting at the table when Lucky andBigman entered the conference room. One was Com­mander Donahue, whose face bore the appearance of a carefully controlled tension. The commander rose andcoldly introduced the other: James Panner, the chiefengineer and civilian head of the project. Panner was astocky man with a swarthy face, dark deep-set eyes, anda bull neck. He wore a dark shirt open at the collar andwithout insignia of any sort.

 Lieutenant Nevsky saluted and retired. CommanderDonahue watched the door close and said, "Since that leaves the four of us, let's get to business."

 "The four of us and a cat," said Lucky, stroking asmall creature that hitched its forepaws on the table and stared at him solemnly. "This isn't the same cat I sawyesterday, is it?"

 The commander frowned. "Perhaps. Perhaps not.We have a number of cats on the satellite. However, Ipresume we're not here to discuss pets."

 Lucky said, "On the contrary, Commander, I think it will do as a topic of conversation to begin with andI chose it deliberately. Do you remember my own pet,sir?"

 "Your little Venusian creature?" said the com­mander with sudden warmth. "I remember it. It was—"He stopped in confusion as though wondering, in the V-frog's absence, what the reason for his enthusiasmconcerning it might be.

 76                         

 "The little Venusian creature," said Lucky, "had peculiar abilities. It could detect emotion. It couldtransmit emotion. It could even impose emotion."

 The commander's eyes opened wide, but Panner saidin a husky voice, "I once heard a rumor to that effect, Councilman. I laughed."

 "You needn't have. It is true. In fact, CommanderDonahue, my purpose in asking for this interview wasto make arrangements to have every man on the projectinterviewed by me in the presence of the V-frog. Iwanted an emotional analysis."

 The commander still seemed half stunned. "Whatwould that prove?"

 "Perhaps nothing. Still, I meant to try it."

 Panner intervened."Meant to try it? You use thepast tense, Councilman Starr."

 Lucky stared solemnly at the two project officials."My V-frog is dead."

 Bigman said furiously, "Killed this morning."

 The commander said, "Who killed it?"

 "We don't know, Commander."

 The commander sat back in his chair. "Then yourlittle investigation is over, I suppose, till the animal can be replaced."

 Lucky said, "There will be no waiting. The mere factof the V-frog's death has told me a great deal, and thematter becomes much more serious."

 "What do you mean?"

 All stared. Even Bigman looked up at Lucky in pro­found surprise.

 Lucky said, "I told you that the V-frog has thecapacity to impose emotion. You yourself, CommanderDonahue, experienced that. Do you recall your feelings

                                                                                77

 when you saw the V-frog on my ship yesterday? Youwere under considerable strain, yet when you saw theV-frog— Do you remember your feelings, sir?"

 "I was rather taken with the creature," the com­mander faltered.

 "Can you think why, as you look back at the momentnow?"

 "No, come to think of it. Ugly creature."

 "Yet you liked it. You couldn't help yourself. Couldyou have harmed it?"

 "I suppose not."

 "I'm certain you couldn't. No one with emotionscould have. Yet someone did. Someone killed it."

 Panner said, "Do you intend to explain the paradox?"

 "Easily explained. No onewith emotions, A robot,however, doesnot have emotions. Suppose that some­where on Jupiter Nine there is a robot, a mechanical man, in the perfect form of a human being?"

 "You mean a humanoid?" exploded Commander Donahue. "Impossible. Such things exist only in fairy tales."

 Lucky said, "I think, Commander, you are not awareof how skillful the Sirians are in the manufacture of robots. I think they might be able to use some man onJupiter Nine, some thoroughly loyal man, as model;build a robot in his shape and substitute it for him.Such a humanoid robot could have special senses thatwould enable it to be the perfect spy. It might, for instance, be able to see in the dark or sense things through thicknesses of matter. It would certainly beable to transmit information through the subether bysome built-in device."

 The commander shook his head. "Ridiculous. A man

 78                         

 could easily have killed the V-frog. A desperate manfrightened to an extreme might have overcome this—this mental influence the animal exerted. Have you thought of that?"

 "Yes, I have," said Lucky. "But why should a manbe so desperate, why so wild to kill a harmless V-frog?The most obvious reason is that the V-frog represented a desperate danger, that it was not harmless at all. The only danger a V-frog might have to the killer would involve the animal's capacity to detect and transmit the killer's emotions. Suppose those emotions would be an immediate giveaway to the fact that the killer was aspy?"

 "How could it be?" Panner asked.

 Lucky turned to look at him. "What if our killer had no emotions at all? Wouldn't a man without emotionsbe revealed at once as a robot?... Or take it anotherway altogether. Why kill only the V-frog? Havinggotten into our rooms, having risked so much, havingfound one of us in the shower and one at the intercom and both unsuspecting and unready, why did not thekiller killus instead of the V-frog? For that matter, whynot kill usand the V-frog?"

 "No time, probably," said the commander.

 "There's another and more plausible reason," saidLucky. "Do you know the Three Laws of Robotics, the rules of behavior that all robots are built to follow?"

 "I know them generally," the commander said. "Ican't quote them."

 "I can," said Lucky, "and with your permission Iwill, so that I may make a point. The First Law is this:A robot may not injure a human being or, throughinaction, allow a human being to come to harm. The

                                                                                79

 Second Law is: A robot must obey the orders given itby human beings except where such orders wouldconflict with the First Law. The Third Law is: Arobot must protect its own existence as long as such protection does not conflict with the First or SecondLaw."

 Panner nodded. "All right, Councilman, what doesthat prove?"

 "A robot can be ordered to kill the V-frog, whichis an animal. It will risk its existence, since self-preservation is only Third Law, to obey orders, whichis Second Law. But it cannot be ordered to kill Bigmanor myself, since we are humans, and First Law takesprecedence over all. A human spy would have killed usand the V-frog; a robot spy would have killed only theV-frog. It all points to the same thing, Commander."

 The commander considered that for long minutes,sitting motionless, the lines on his tired face groovingdeeper. Then he said, "What do you propose to do?X-ray every man on the project?"

 "No," said Lucky at once. "It's not that simple.Successful espionage is going on elsewhere than here. Ifthere is a humanoid robot here, there are probablyothers elsewhere. It would be well to catch as many of the humanoids as possible; all of them if we can. If weact too eagerly and openly to catch the one under our hands, the others may be snatched away for use atanother time."

 "Then whatdo you propose doing?"

 "To work slowly. Once you suspect a robot, there areways of making it give itself away without its beingaware of it. And I don't start completely from scratch.For instance, Commander, I know you are not a robot,

 80                        

 since I detected emotion in you yesterday. In fact, Ideliberately induced anger in you to test my V-frog,and for that I ask your pardon."

 Donahue's face had gone mauve. "I, a robot?"

 "As I said, I used you only to test my V-frog."

 Panner said dryly, "You have no reason to feel sureabout me, Councilman. I never faced your V-frog."

 "That is right," said Lucky. "You are not clearedyet. Remove your shirt."

 "What!" cried Panner indignantly. "Why?"

 Lucky said mildly, "You have just been cleared. Arobot would have had to obey that order."

 The commander's fist banged down on his desk."Stop it!This ends right here. I will not have you test­ing or annoying my men in any way. I have a job to doon this satellite, Councilman Starr; I have an Agravship to get into space, and I'm getting it into space. Mymen have been investigated and they're clear. Yourstory about a robot is flimsy, and I'm not going alongwith it.

 "I told you yesterday, Starr, that I didn't want youon this satellite disturbing my men and wrecking theirmorale. You saw fit yesterday to address me in insultingfashion. You say now it was just to test your animal, which makes it no less insulting. For that reason, I feel no need to co-operate with you and I am not doing so.Let me tell you exactly what I have done.

 "I've cut off all communication with Earth. I've putJupiter Nine under emergency orders. I have thepowers of a military dictator now. Do you understand?"

 Lucky's eyes narrowed a trifle. "As councilman ofthe Council of Science, I outrank you."

 "How do you intend to enforce your rank? My men

 81

 will obey me and they have their orders. You will berestrained forcibly if you try in any way, by word ordeed, to interfere with my orders."

 "And what are your orders?"

 "Tomorrow," said Commander Donahue, "at 6p.m.,Solar Standard Time, the first functioning Agrav shipin existence will make its first flight from Jupiter Nineto Jupiter One, the satellite lo. After we're back—afterwe're back, Councilman Starr, and not one hour sooner—you may conduct your investigation. And ifyou then want to get in touch with Earth and arrangecourt-martial proceedings, I will be ready for you."

 Commander Donahue stared firmly at Lucky Starr.

 Lucky said to Panner, "Is the ship ready?"

 PFanner said, "I think so."

 Donahue said scornfully. "We leave tomorrow. Well,Councilman Starr, do you go along with me or will Ihave to have you arrested?"

 The silence that followed was a tense one. Bigmanvirtually held his breath. The commander's hands wereclenching and unclenching, and his nose was white andpinched. Panner slowly fumbled a stick of gum out of his shirt pocket, stripped it of its plastofoil coating withone hand, and crumpled it into his mouth.

 And then Lucky clasped his hands loosely, sat backin his chair, and said, "I'll be glad to co-operate with you, Commander."

 8

 Blindness

 Bigman was at once outraged. "Lucky! Are you goingto let him stop the investigation just like that?"

 Lucky said, "Not exactly, Bigman. We'll be on boardthe Agrav ship and we'll continue it there."

 "No sir," the commander said flatly, "You will notbe on board. Don't think that for an instant."

 Lucky said, "Who will be on board, Commander?Yourself, I presume?"

 "Myself. Also Panner, as chief engineer. Two of my officers, five other engineers, and five ordinary crew­men. All these were chosen some time ago. Myself and Panner, as responsible heads of the project; the fiveengineers to handle the ship itself; the remainder in return for their services to the project."

 Lucky said thoughtfully, "What type of service?"

 Panner interrupted to say, "The best example ofwhat the commander is talking about is Harry Norrich,who—"

 Bigman stiffened in surprise. "You mean the blindfellow?"

 83

 84                        

 Panner said, "You know him then?"

 "We met him last evening," said Lucky.

 "Well," said Panner, "Norrich was here at the verybeginning of the project. He lost his sight when hethrew himself between two contacts to keep a force fieldfrom buckling. He was in the hospital five months andhis eyes were the one part of him that couldn't be re­stored. By his act of bravery, he kept the satellite from having a chunk the size of a mountain blown out of it.He saved the lives of two hundred peopleand he savedthe project, since a major accident at the beginningmight have made it impossible to get further appro­priations out of Congress. That sort of thing is whatearns one the honor of a place on the maiden voyage ofthe Agrav ship."

 "It's a shame he won't be able to see Jupiter upclose," said Bigman. Then, his eyes narrowing, "How'llhe get around on board ship?"

 Panner said, "We'll be taking Mutt, Fm sure. He's awell-behaved dog."

 "That's all I want to know then," said Bigman heat­edly. "If you cobbers can take a dog, you can takeLucky and me."

 Commander Donahue was looking at his wristwatchimpatiently. Now he put the palms of his hands flat onthe table; and made as though to rise. "We have finishedour business then, gentlemen."

 "Not quite," Lucky said. "There's one little point tobe cleared up. Bigman puts it crudely, but he's quiteright. He and I will be on the Agrav ship when itleaves."

 "No," said Commander Donahue. "Impossible."

                                                                                 85

 "Is the added mass of two individuals too great forthe ship to handle?"

 Panner laughed. "We could move a mountain."

 "Do you lack room then?"

 The commander stared at Lucky in hard displeasure."I will not give any reason. You are not being takenonly because it is my decision that you not be taken. Isthat clear?"

 There was a glint of satisfaction in his eyes, andLucky did not find it hard to guess that he was squaringaccounts for the tongue-lashing Lucky had given himaboard theLucky Starr.

 Lucky said quietly, "You had better take us, Com­mander."

 Donahue smiled sardonically. "Why? Am I to berelieved of duty at the orders of the Council of Science?You won't be able to communicate with Earth till Ireturn, and after that they can relieve me of duty ifthey wish."

 "I don't think you've thought it through, Com­mander," said Lucky. "They might relieve you of dutyretroactive to this moment. In fact, I assure you theywill do so. As far as the government records are con­cerned, then, it will appear that Agrav ship made itsfirst flight not under your command but under the com­mand, officially, of your successor, whoever he mightbe. The records of the trip might even be adjusted to show, officially, that you were not on board."

 Commander Donahue went white. He rose and fora moment seemed on the point of throwing himselfbodily at Lucky.

 Lucky said, "Your decision, Commander?"

 86                         

 Donahue's voice was most unnatural when it finally came. "You may come."

 Lucky spent the remainder of the day in the recordrooms, studying the files on various men employed on the project, while Bigman, under Panner's guidance, was taken from laboratory to laboratory and throughtremendous testing rooms.

 It was only after the evening meal when they returnedto quarters that they had a chance to be alone together.Lucky's silence then was not extraordinary, since the young councilman was never talkative at the best oftimes, but there was a small crease between his eyesthat Bigman recognized as a sure sign of concern.

 Bigman said, "We aren't making any progress, arewe, Lucky?"

 Lucky shook his head, "Nothing startling, I'll admit:"

 He had brought a book-film with him from theproject's library, and Bigman caught a flash of its title:Advanced Robotics.Methodically Lucky threaded thebeginnings of the film through the viewer.

 Bigman stirred restlessly. "Are you going to be alltied up with that film, Lucky?"

 "I'm afraid so, Bigman."

 "Do you mind then if I visit Norrich next door forcompany?"

 "Go ahead." Lucky had the viewer over his eyes andhe was leaning back, his arms crossed loosely across his chest.

 Bigman closed the door and remained standing just outside for a moment, a little nervous. He should dis­cuss this with Lucky first, he knew he should, and yetthe temptation...

                                                                                87

 He told himself: I'm not going to do anything. I'lljust check something. If I'm wrong, I'm wrong and whybother Lucky? But if it checks out, then I'llreally have something to tell him.

 The door opened at once when he rang, and therewas Norrich, blind eyes fixed in the direction of thedoorway, seated before a desk on which a checkerboarddesign carried odd figures.

 He said, "Yes?"

 "This is Bigman," said the little Martian.

 "Bigman! Come in. Sit down. Is Councilman Starrwith you?"

 The door closed again, and Bigman looked about in the brightly lit room. His mouth tightened. "He's busy. But as for me, I'm filled up on Agrav today. Dr. Pannertook me all over, only I don't understand a thing of ithardly."

 Norrich smiled. "You're not exactly in a minority,but if you ignore the mathematics, some of it isn't toohard to understand."

 "No? Mind explaining it then?" Bigman sat down ina large chair and bent to look under Norrich's work­bench. Mutt lay there with his head between his fore-paws and one eye brightly fixed on Bigman.

 (Keep him talking, thought Bigman. Keep him talk­ing till I find a hole, or make one.)

 "Look here," Norrich said. He held up one of theround counters he had been holding. "Gravity is a form of energy. An object- such as this piece I'm holdingwhich is under the influence of a gravitational field but is not allowed to move is said to have potential energy.If I were to release the piece, that potential energywould be converted to motion—or kinetic energy, as it

 88                        

 is called. Since it continues under the influence of thegravitational field as it falls, it falls faster and faster andfaster." He dropped the counter at this point, and itfell.

 "Until, splash," said Bigman. The counter hit thefloor and rolled.

 Norrich bent as though to retrieve it and then said,"Would you get it for me, Bigman? I'm not sure whereit rolled."

 Bigman suppressed his disappointment. He pickedit up and returned it.

 Norrich said, "Now until recently that was the onlything that could be done with potential energy: it could be converted into kinetic energy. Of course the kineticenergy could be used further. For instance, the fallingwater of Niagara Falls could be used to form electricity,but that's a different thing. In space, gravity results inmotion and that ends it.

 "Consider the Jovian system of moons. We're atJupiter Nine, way out. Fifteen million miles out. Withrespect to Jupiter, we've got a tremendous quantity ofpotential energy. If we try to travel to Jupiter One, thesatellite Io, which is only 285,000 miles from Jupiter,we are in a way, falling all those millions of miles. Wepick up tremendous speeds which we must continuallycounteract by pushing in the opposite direction with ahyperatomic motor. It takes enormous energy. Then,if we miss our mark by a bit, we're in constant dangerof continuing to fall, in which case there's only oneplace to go, and that's Jupiter—and Jupiter is instantdeath.Then, even if we land safely on lo, there's the problem of getting back to Jupiter Nine, which means

                                                                                 89

 lifting ourselves all those millions of miles against Jupi­ter's gravity. The amount of energy required to ma­neuver among Jupiter's moons is just prohibitive."

 "And Agrav?" asked Bigman.

 "Ah! Now that's a different thing. Once you use anAgrav converter, potential energy can be converted into forms of energyother than kinetic energy. In the Agravcorridor, for instance, the force of gravity in one direc­tion is used to charge the gravitational field in the otherdirection as you fall. People falling in one direction provide the energy for people falling in the other. Bybleeding off the energy that way, you yourself, whilefalling, need never speed up. You can fall at any veloc­ity less than the natural falling velocity. You see?"

 Bigman wasn't quite sure he did but he said, "Go on."

 "In space it's different. There's no second gravita­tional field to shift the energy to. Instead, it is con-,verted to hyperatomic field energy and stored so. Bydoing this, a space ship can drop from Jupiter Nine to Io at any speed less than the natural falling speed with­out having to use any energy to decelerate. Virtually noenergy is expended except in the final adjustment to Io'sorbital speed. And safety is complete, since the ship isalways under perfect control. Jupiter's gravity could be completely blanketed, if necessary.

 "Going back to Jupiter Nine still requires energy. There is no getting around that. But now you can usethe energy you had previously stored in the hyper­atomic field condenser to get you back. The energy ofJupiter's own gravitational field is used to kick youback."

 Bigman said, "It sounds good." He squirmed in his

 90                         

 seat. He wasn't getting anywhere. Suddenly he said,"What's that you're fooling with on your desk?"

 "Chess," said Norrich. "Do you play?"

 "A little," Bigman confessed. "Lucky taught me, butit's no fun playing with him. He always wins." Then heasked, offhand, "How canyou play chess?"

 "You mean because I'm blind?"

 "Uh—"

 "It's all right. I'm not sensitive about being blind. ... It's easy enough to explain. This board is magnetizedand the pieces are made of a light magnetic alloy sothat they stick where they're put and don't go tum­bling if I move my arm about carelessly. Here, try it,Bigman."

 Bigman reached for one of the pieces. It came up asthough stuck in syrup for a quarter of an inch or so,then was free.

 "And you see," said Norrich, "they're not ordinarychess pieces."

 "More like checkers," grunted Bigman.

 "Again so I don't knock them over. They're not com­pletely flat, though. They've got raised designs whichI can identify easily enough by touch and which resem­ble the ordinary pieces closely enough so that other people can learn them in a moment and play with me.See for yourself."

 Bigman had no trouble. The circle of raised pointswas obviously the queen, while the little cross in thecenter of another piece signified the king. The pieceswith grooves slanting across were the bishops, the raisedcircle of squares the rooks, the pointed horse's ears theknights, and the simple round knobs the pawns.

 91

 Bigman felt stymied. He said, "What are you doing now? Playing a game by yourself?"

 "No, solving a problem. The pieces are arranged just so, you see, and there's one way and only one in which white can win the game in exactly three moves and I'mtrying to find that way."

 Bigman said suddenly, "How can you tell white fromblack?"

 Norrich laughed. "If you'll look closely, you'll see the white pieces are grooved along the rims and the black pieces aren't."

 "Oh. Then you have to remember where all thepieces are, don't you?"

 "That's not hard," Norrich said. "It sounds as thoughyou would need a photographic memory, but actuallyall I have to do is pass my hand over the board and check the pieces any time. You'll notice the squaresare marked off by little grooves, too."

 Bigman found himself breathing hard. He had for­gotten about the squares on the checkerboard, and theywere grooved off. He felt as though he were playing a kind of a chess game of Ms own, one in which he was being badly beaten.

 "Mind if I watch?" he said sharply. "Maybe I canfigure out the right moves."

 "By all means," said Norrich. "I wish you could.I've been at this for half an hour and I'm gettingfrustrated."

 There was silence for a minute or more, and thenBigman rose, his body tense and catlike in its effort to make no noise. He drew a small flashlight from onepocket and stepped toward the wall in little motions.Norrich never moved from his bowed position over the

 92                                 

 chessboard. Bigman threw a quick glance toward Mutt,but the dog made no move, either.

 Bigman reached the wall and, hardly breathing, putone hand lightly and noiselessly over the light patch.At once, the light in the room went out and a profounddarkness rested everywhere.

 Bigman remembered the direction in which Norrich'schair was. He raised the flashlight.

 He heard a muted thump and then Norrich's voicecalling out in surprise and a little displeasure, "Whydid you put out the light, Bigman?"

 "That does it," yelled Bigman in triumph. He let theflashlight's beam shine full on Norrich's broad face."You're not blind at all, you spy."

 9

 The Agrav Ship

 Norrich cried out, "I don't know what you're doing,but Space, man, don't do anything sudden or Mutt will jump you!"

 "You know exactly what I'm doing," said Bigman,"because you can see well enough I'm drawing myneedle-gun, and I think you've heard I'm a dead shot.If your dog moves in my direction, it's the end for him."

 "Don't hurt Mutt. Please!"

 Bigman was taken aback by the sudden anguish inthe other's voice. He said, "Just keep him quiet then and come with me and no one will be hurt. We'll gosee Lucky. And if we pass anyone in the corridor, don'tyou say anything but 'Good day.' I'll be right besideyou, you know."

 Norrich said, "I can't go without Mutt."

 "Sure you can," said Bigman. "It's only five stepsdown the corridor. Even if you were really blind, youcould manage that—a fellow who can do threedeesand all."

 Lucky lifted the viewer from his head at the sound of

 93

 94                         

 the door opening and said, "Good day, Norrich. Where'sMutt?"

 Bigman spoke before the other had a chance toanswer. "Mutt's in Norrich's room, and Norrich doesn'tneed him. Sands of Mars. Lucky, Norrich isn't anyblinder than we are!"

 "What?"

 Norrich began, "Your friend is quite mistaken, Mr.Starr. I want to say—"

 Bigman snapped. "Quiet, you! I'll talk, and thenwhen you're invited, you can make some remarks."

 Lucky folded his arms. "If you don't mind, Mr. Nor­rich, I'd like to hear what Bigman has on his mind.And meanwhile, Bigman, suppose you put away theneedle-gun."

 Bigman did so with a grimace. He said, "Look,Lucky, I suspected this cobber from the beginning. Those threedee puzzles of his set me to thinking. Hewas just a little too good. I got to wondering right away that he might be the spy."

 "That's the second time you've called me a spy,"Norrich cried. "I won't stand for that."

 "Look, Lucky," said Bigman, ignoring Norrich's out­cry, "it would be a clever move to have a spy a supposedblind man. He could see an awful lot no one wouldthink he was seeing. People wouldn't cover up. Theywouldn't hide things. He could be staring right at somevital document and they'd think, 'It's only poor Nor­rich. He can't see.' More likely they wouldn't give it athought at all. Sands of Mars, it would be a perfectsetup!"

 Norrich was looking more astonished with every

                                                                                95

 moment. "But Iam blind. If it's the threedee puzzles orthe chess, I've explained—"

 "Oh, sure, you've explained," Bigman said scorn­fully. "You've been practicing explanations for years.How come you sit in the privacy of your room with thelights on, though? When I walked in, Lucky, about halfan hour ago, the light was on. He hadn't just put it onfor me. The switch was too far away from where he wassitting. Why?"

 "Why not?" said Norrich. "It makes no differenceto me whether it's on or not, so it might as well be onas long as I'm awake for the convenience of those who come visiting, like you."

 "All right," said Bigman. "That shows how he canthink up an explanation for everything—how he canplay chess, how he can identify the pieces, everything.Once he almost forgot himself. He dropped one of hischess pieces and bent to pick it up when he rememberedjust in time and asked me to do it for him."

 "Usually," said Norrich, "I can tell where somethingdrops by the sound. This piece rolled."

 "Go on, explain," said Bigman. "It won't help youbecause there's one thing youcan't explain. Lucky, Iwas going to test him. I was going to put out the light,then flash my pocketlight in his eyes at full intensity.If he weren't blind, he'd be bound to jump or blink his eyes anyway. I was sure I'd get him. But I didn't evenhave to go that far. As soon as I put out the light, thepoor cobber forgets himself and says, 'Why did you put out the light?'. .. How did he know I put out the light,Lucky?How did he know?"

 "But—" Norrich began.

 Bigman drove on. "He can feel chess pieces and

 96                        

 threedee puzzles and all that but he can't feel lightgoing out. He had tosee that."

 Lucky said, "I think it's time to let Mr. Norrich saysomething."

 Norrich said, "Thank you. I may be blind, Council­man, but my dog is not. When I put out the light atnight, it makes no difference to me, as I said before, butto Mutt it signals bedtime and he goes to his own cor­ner. Now I heard Bigman tiptoe to the wall in thedirection of the light switch. He was trying to movewithout sound, but a man who has been blind for fiveyears can hear the lightest tiptoe. A moment after hestopped walking I heard Mutt jump into his corner.It didn't take much brain power to figure out what hadhappened. Bigman was standing at the light switch andMutt was turning in for the night. Obviously he hadput out the light."

 The engineer turned his sightless face in the directionfirst of Bigman, then of Lucky, as though straining his ears for an answer.

 Lucky said, "Yes, I see. It seems we owe you anapology."

 Bigman's gnomelike face screwed up unhappily."But Lucky—"

 Lucky shook his head. "Let go, Bigman! Never hangon to a theory after it's been exploded. I hope youunderstand, Mr. Norrich, that Bigman was only doingwhat he felt to be his duty."

 "I wish he had asked a few questions before acting,''said Norrich, coldly, "Now may I go? Do you mind?"

 "You may go. As an official request, however, pleasemake no mention of what has occurred to anyone.That's quite important."

                                                                                97

 Norrich said, "It comes under the heading of falsearrest, I imagine, but we'll let it go. I won't mentionthis." He walked to the door, reached the signal patch with a minimum of fumbling, and walked out.

 Bigman turned almost at once to Lucky. "It was atrick. You shouldn't have let him go."

 Lucky, rested his chin on the palm of his right hand, and his calm, brown eyes were thoughtful. "No, Big­man, he isn't the man we're after."

 "But he'sgot to be, Lucky. Even if he's blind,reallyblind, it's an argument against him. Sure, Lucky," Big­man grew excited again, his small hands clumping intofists, "he could get close to the V-frog without seeingit. He could kill it."

 Lucky shook his head. "No, Bigman. The V-frog's mental influence doesn't depend on its being seen. It'sdirect mental contact. That's the one fact we can't getaround." He said slowly, "It had to be a robot who didthat. It had to be, and Norrich is no robot."

 "Well, how do you know he—?" But Bigmanstopped.

 "I see you've answered your own question. We sensedhis emotion during our first meeting, when the V-frogwas still with us. He has emotions, so he's not the robotand he's not the man we're looking for."

 But even as he said so, there was a look of deeptrouble on his face and he tossed the book-film onadvanced robotics to one side as though despairing ofhelp from it.

 The first Agrav ship ever to be built was namedJovian Moonand it was not like any ship Lucky hadever seen. It was large enough to be a luxury liner of

 98                         

 space, but the crew and passenger quarters were ab­normally crowded forward,. since nine tenths of theship's volume consisted of the Agrav converter and thehyperatomic force-field condensers. From the midsec-tion, curved vanes, ridged into a vague resemblance tobat's wings, extended on either side. Five to one side, five to the other, ten in all.

 Lucky had been told that these vanes, in cutting the lines of force of the gravitational field, converted thegravity into hyperatomic energy. It was as prosaic as that, and yet they gave the ship an almost sinisterappearance.

 The ship rested now in a gigantic pit dug into JupiterNine. The lid, of reinforced concrete, had been re­tracted, and the whole area was under normal JupiterNine gravity and exposed to the normal airlessness ofJupiter Nine's surface.

 Nevertheless the entire personnel of the project, nearly a thousand men, were gathered in this naturalamphitheater. Lucky had never seen so many men inspace suits at one time. There was a certain naturalexcitement because of the occasion; a certain almosthysterical restlessness that manifested itself in horseplaymade possible by the low gravity.

 Lucky thought grimly: And one of those men inspace suits is no man at all.

 But which one? And how could he tell?

 Commander Donahue made his short speech of dedi­cation to a group of men grown silent, impressed despitethemselves; while Lucky, looking up at Jupiter, glancedat a small object near it that was not a star but a tinysliver of light, curved like the paring of a small finger­nail, almost too small for the curve to be seen. If there

                                                                                99

 had been any air in the way, instead of Jupiter Nine'sairless vacuum, that small curve would have beenblurred into a formless spot of light.

 Lucky knew the tiny crescent to be Ganymede, Jupi­ter Three, Jupiter's largest satellite and worthy moonof the giant planet. It was nearly three times the size ofEarth's moon; it was larger than the planet Mercury.It was almost as large as Mars. With the Agrav fleetcompleted, Ganymede would quickly become a major world of the solar system.

 Commander Donahue christened the ship at last ina voice husky with emotion, and then the assembledaudience, in groups of five and six, entered the air-filledinterior of the satellite through the various locks.

 Only those who were to be aboard theJovian Moonremained. One by one they climbed the ramp to theentrance lock, Commander Donahue first.

 Lucky and Bigman were last to board. CommanderDonahue turned away from the air lock as they entered,stiffly unfriendly.

 Bigman leaned toward Lucky, to say tightly, "Did you notice, Lucky, that Red Summers is on board?"

 "I know."

 "He's the cobber who tried to kill you."

 "I know, Bigman."

 The ship was lifting now in what was at first a majes­tic creep. The surface gravity of Jupiter Nine wasonly one eightieth of Earth, and though the weightof the ship was still in the hundreds of tons, that wasnot the cause of the initial slowness. Even were gravity absent altogether, the ship would still retain its full con­tent of matter and all the inertia that went with it. It

 100                       

 would still be just as hard to put all that matter into motion, or, if it came to that, to stop it or change itsdirection of travel, once it had begun moving.

 But first slowly, then more and more rapidly, the pitwas left behind. Jupiter Nine shrank beneath them andbecame visible in the visiplatps as a rugged gray rock.The constellations powdered the black sky and Jupiterwas a bright marble.

 James Panner approached them and placed an armon the shoulder of each man. "Would you two gentle­men care to join me in my cabin for a meal? There'llbe nothing to watch here in the viewing room for awhile." His wide mouth pulled back in a grin thatswelled the cords of his thick neck and made it seem noneck at all but a mere continuation of head.

 "Thank you," Lucky said. "It's kind of you to inviteus."

 "Well," said Panner, "the commander isn't going toand the men are a little leery of you, too. I don't want you to get too lonely. It will be a long trip."

 "Aren't you leery of me, Dr. Panner?" Lucky askeddryly.

 "Of course not. You tested me, remember, and Ipassed."

 Panner's cabin was a small one in which the threebarely fitted. It was obvious that the quarters in this,the first Agrav ship, were as cramped as engineeringingenuity could make them. Panner broke out threecans of ship-ration, the concentrated food that was uni­versally eaten on space ships. It was almost home to Lucky and Bigman; the smell of heating rations, thefeeling of crowding walls, outside of which was the

                                                                               101

 infinite emptiness of space, and, sounding through thosewalls, the steady vibrating hum of hyperatomic motorsconverting field energies into a directional thrust or, atthe very least, powering the energy-consuming innardsof the ship.

 If ever the ancient belief of the "music of the spheres"could be said to have come literally true, it was in thathum of hyperatomics that was the very essential ofspace flight.

 Panner said, "We're past Jupiter Nine's escape veloc­ity now, which means we can coast without danger offalling back to its surface."

 Lucky said, "That means we're in free fall down toJupiter."

 "With fifteen million miles to fall, yes. Once we've piled up enough velocity to make it worthwhile, we'llshift to Agrav."

 , He took a watch out of his pocket as he spoke. It wasa large disc of gleaming, featureless metal. He pressed a small catch, and luminous figures appeared upon itsface. A glowing line of white encircled it, turning redin a sweeping arc until the redness closed in upon itselfand the arc turned white again.

 Lucky said, "Are we scheduled to enter Agrav sosoon?"

 "Not very long," said Panner. He placed the watchon the table, and they ate silently.

 Panner lifted the watch again. "A little under a min­ute. It should be completely automatic." Although thechief engineer spoke calmly enough, the hand that heldthe watch trembled very slightly.

 Panner said, "Now," and there was silence. Completesilence.

 102                       

 The hum of the hyperatomics had stopped. The very power to keep the ship's lights on and its pseudo-gravfield in operation were now coming from Jupiter's grav­itational field.

 Panner said, "On the nose! Perfect!" He put awayhis watch, and though the smile on his broad, homelyface was a restrained one, it virtually shouted relief."We're actually on an Agrav ship now in full Agrav operation."

 Lucky was smiling, too. "Congratulations. I'mpleased to be on board."

 "I imagine you are. You worked hard enough for it.Poor Donahue."

 Lucky said gravely, ''I'm sorry I had to push thecommander so hard, but I had no choice. One way oranother, I had to be on board."

 Panner's eyes narrowed at the sudden gravity inLucky's voice."Had to be?"

 "Had to be! It seems almost certain to me that onboard this ship at the present moment is the spy we'relooking for."

 10

 In the Vitals of the Ship

 Panner stared blankly. Then, "Why?"

 "The Sirians would certainly want to know how theship actually worked. If their method of spying is fool­proof, as it has been till now, why not continue it on board the ship?"

 "What you're saying, then, is that one of the fourteenmen on board theJovian Moon is a robot?"

 "That is exactly what I mean."

 "But the men aboard ship have been chosen longsince."

 "The Sirians would know the reasons for choosingand the method of choice just as they know everythingelse about the project and they would maneuver their humanoid robot so as to have him chosen."

 "That's giving them a lot of credit," muttered Panner.

 "I admit it," said Lucky. "There is an alternative."

 "Which is?"

 "That the humanoid robot is aboard as a stowaway."

 "Very unlikely," said Panner.

 "But quite possible. It might easily have boarded the

 103

 104                              

 ship in the confusion before the commander made hischristening speech. I tried to watch the ship then, butit was impossible. Furthermore, nine tenths of the ship seems to be made up of engine compartment, so theremust be plenty of room to hide."

 Panner thought about it. "Not as much room as you might think."

 "Still we must search the ship. Will you do that, Dr. Panner?"

 "I?"

 "Certainly. As chief engineer, you would know the contents of the engine compartment better than anyoneelse. We'll go with you."

 "Wait. It's a fool's errand."

 "If there is no stowaway, Dr. Panner, we have stillgained something. We'll know we can restrict our con­sideration to the men legally aboard ship."

 "Just three of us?"

 Lucky said quietly, "Whom can we trust to help us,when anyone we might ask might be the robot we're looking for? Let us not discuss this any further, Dr. Panner. Are you willing to help us search the ship? Iam asking your help in my capacity as a member ofthe Council of Science."

 Reluctantly Panner got to his feet. "I suppose I mustthen."

 They clambered down the hand holds of the narrow shaft leading to the first engine level. The light was subdued and, naturally, indirect, so that the huge struc­tures on either side cast no shadow.

 There was no sound, no slightest hum to indicate activity or to show that vast forces were being trapped

                                                                               105

 and dealt with. Bigman, looking about, was appalled tofind that nothing seemed familiar; that of the ordinaryworkings of a space ship, such as that of their ownShooting Starr,nothing seemed left.

 "Everything's closed in," he said.

 Panner nodded and said in a low voice, "Everythingis as automatic as possible. The need for human inter­vention has been cut to the minimum."

 "What about repairs?"

 "There shouldn't have to be any," the engineer said grimly. "We have alternate circuits and duplicatedequipment at every step, all allowing for automaticcut-in after self-check."

 Panner moved ahead, guiding them through thenarrow openings but moving always slowly as thoughat any moment he expected someone, or some thing, tohurl itself murderously upon them.

 Level by level, methodically moving out from thecentral shaft along the side channels, Panner probedeach bit of room with the sureness of the expert.

 Eventually they came to a halt at the very bottom,hard against the large tail jets through which the glow­ing hyperatomic forces (when the ship was in ordinaryflight) pressed backward to push the ship forward.

 From within the ship the test jets showed as foursmooth pipes, each twice as thick as a man, burrowinginto the ship and ending in the tremendous featurelessstructures that housed the hyperatomic motors.

 Bigman, said, "Hey, the jets! Inside!"

 "No," said Panner.

 "Why not? A robot could hide there fine. It's openspace, but what's that to a robot?"

 "Hyperatomic thrusts," said Lucky, "would be plenty

 106                       

 to it and there've been a number of those till an hourago. No, the jets are out."

 "Well, then," said Panner, "there's no one anywherein the engine compartments. No thing, either."

 "You're sure?"

 "Yes. There isn't a place we haven't looked, and theroute I followed made it impossible for anything to getaround and behind us."

 Their voices made small echoes in the lengths ofshafts behind them.

 Bigman said, "Sands of Mars, that leaves us withthe fourteen regulars."

 Lucky said thoughtfully, "Less than that. Three ofthe men aboard ship showed emotion: CommanderDonahue, Harry Norrich, Red Summers. That leaveseleven."

 Panner said, "Don't forget me. I disobeyed an order.That leaves ten."

 "That raises an interesting point," said Lucky. "Doyou know anything about robotics?"

 "I?" said Panner. "Never dealt with a robot in mylife."

 "Exactly," said Lucky. "Earthmen invented thepositronic robot and developed most of the refinements,yet, except for a few specialists, the Earth technicianknows nothing about robotics, simply because wedon't use robots to any extent. It isn't taught in theschools and it doesn't come up in practice. I myselfknow the Three Laws and not too much more. Com­mander Donahue couldn't even quote the Three Laws.The Sirians, on the other hand, with a robot-saturatedeconomy, must be past masters at all the subtleties ofrobotics.

                                                                               107

 "Now I spent a good deal of time yesterday and to­day with a book-film on advanced robotics, that Ifound in the project library. It was the only book onthe subject, by the way."

 "So?" said Panner.

 "It became obvious to me that the Three Laws aren'tas simple as one might think. . . . Let us move on, bythe way. We can give the engine levels a double checkon the way back." He was moving across this lowest level as he spoke, looking with keen interest at hissurroundings.

 Lucky continued, "For instance, I might think itwould only be necessary to give each man on the shipa ridiculous order and note whether it be obeyed. As a matter of fact, I did think so. But that isn't necessarilytrue. It is theoretically possible to adjust the positronic brain of a robot to obey only those orders that belong naturally to the line of its duties. Orders that are con­trary to those duties or irrelevant to them may still beobeyed provided that they are preceded by certainwords which act as a code or by the person who givesthe orders identifying himself in a certain way. In thismanner a robot can be handled in all ways by itsproper overseers and yet be insensitive to strangers."

 Panner, who had placed his hands on the holds that would guide the men up to the next higher level, re­leased them. He turned to face Lucky.

 He said, "You mean when you told me to take offmy shirt and I didn't obey, that meant nothing?"

 "I say it could have meant nothing, Dr. Panner, sincetaking off your shirt at that moment was no part ofyour regular duties, and my order might not have beenstated in the proper form."

 108                       

 "Then you're accusing me of being a robot?"

 "No. It isn't likely that you are. The Sirians, inchoosing some member of the project to replace by arobot, would scarcely choose the chief engineer. Forthe robot to do that job properly, it would have toknow so much about Agrav that the Sirians couldn't supply the knowledge. Or, if they could, they wouldhave no need to spy."

 "Thanks," said Panner, sourly, turning toward thehand holds again, but now Bigman's voice rang out.

 "Hold it, Panner!" The small Martian had his readyneedle-gun in his fist. He said, "Wait a minute, Lucky,how do we know he knows anything about Agrav?We're just assuming that. He never showed us anyknowledge. When theJovian Moon shifted to Agrav,where was he? Sitting on his squatter in his quarterswith us, that's where he was."

 Lucky said, "I thought of that, too, Bigman, andthat's one reason I brought Panner down here. He'sobviously acquainted with the engines. I've watchedhim inspect everything and he couldn't have done itwith such assurance if he weren't an expert on theworkings."

 "Does that suit you, Martian?" Panner demanded with suppressed anger.

 Bigman put his needle-gun away, and without afurther word Panner scrambled up the ladder.

 They stopped off at the next level, working throughit a second time.

 Panner said, "All right, that leaves ten men: two army officers, four engineers, four workmen. Whatdp you propose to do? X-ray each of them separately?Something like that?"

                                                                               109

 Lucky shook his head. "That's too risky. Apparentlythe Sirians have been known to use a cute little trickto protect themselves. They've been known to use ro­bots to carry messages or to perform tasks which the individual giving the orders wanted to be kept secret.Now obviously a robot can't keep a secret if a humanbeing asks him, in the proper fashion, to reveal it.What the Sirians do, then, is to install an explosive de­vice in the robot which is triggered by any attempt to force the robot to give away the secret."

 "You mean if you put an X-ray on the robot, it willexplode?"

 "There's a very good chance that it would. Its great­est secret is its identity, and it may be triggered forevery attempt to discover that identity that the Sirians could think of." Lucky added regretfully, "They hadn'tcounted on a V-frog; there was no trigger against that.They had to order the robot to kill the V-frog directly. Or that might have been preferable anyway, since itmanaged to keep the robot alive undetected."

 "Wouldn't the robot be harming humans nearby ifit exploded? Wouldn't it be breaking First Law?" asked Panner with a trace of sarcasm.

 "Itwouldn't. It would have no control over the ex­plosion. The triggering would be the result of thesound of a certain question or the sight of a certainaction, not the result of anything the robot itselfwould do."

 They crawled up to still another level.

 "Then what do you expect to do, Councilman?" de­manded Panner.

 "I don't know," Lucky said frankly. "The robot mustbe made to give itself away somehow. The Three Laws,

 110                       

 however modified and fancified,must apply. It's onlya question of being sufficiently acquainted with roboticsto know how to take advantage of those Laws. If Iknew how to force the robot into some action thatwould show it to be non-human without activating anyexplosive device with which it might be equipped; if I could manipulate the Three Laws so as to force oneto conflict with another sufficiently strongly to para­lyze the creature completely; if I—"

 Panner broke in impatiently, "Well, if you expecthelp from me, Councilman, it's no use. I've told youalready I know nothing of robotics." He whirled sud­denly. "What's that?"

 Bigman looked about, too. "I didn't hear any­thing."

 Wordlessly Panner squeezed past them, dwarfedby the bending metal tube on either side.

 He had gone almost as far as he could, the other two following, when he muttered, "Someone might havesqueezed in among the rectifiers. Let me pass again."

 Lucky stared, frowning, into what was almost aforest of twisting cables that enclosed them in a com­plete dead end.

 Lucky said, "It seems clear to me."

 "We can test it for sure," Panner said tightly. Hehad opened a panel in the wall nearby and now hereached in cautiously, looking over his shoulder.

 "Don't move," he said.

 Bigman said testily, "Nothing's happened. There'snothing there."

 Panner relaxed. "I know it. I asked you not to move because I didn't want to slice an arm off when I es­tablished the force field."

                                                                               111

 "What force field?"

 "I've shorted a force field right across the corridor.You can't move out of there any more than you couldif you were encased in solid steel three feet thick."

 Bigman yelled, "Sands of Mars, Lucky, heis therobot!" His hand lunged.

 Panner cried at once, "Don't try the needle-gun.Kill me and how do you ever get out?" He stared atthem, dark eyes sparking, his broad shoulders hunched."Remember, energy can get through a force field butmatter can't, not even air molecules. You're airtightin there. Kill me and you'll suffocate long before any­one happens to come across you down here."

 "I said he was the robot," said Bigman in ragingdespair.

 Panner laughed shortly, "You're wrong. I'm not arobot. But if thereis one, I know who it is."

 11

 Down the Line of Moons

 "Who?" Bigman demanded at once.

 But it was Lucky who answered. "Obviously hethinks it's one of us."

 "Thanks!" said Panner. "How wouldyou explainit? You mentioned stowaways; you talked about peo­ple forcing their way on board theJovian Moon. Talkabout nerve! Aren't there two people who did forcetheir way on board? Didn't I witness the process?Youtwo!"

 "True enough," said Lucky.

 "And you brought me down here so you could in­vestigate every inch of the ship's workings. You triedto keep me busy with stories about robots hoping Iwouldn't notice that you two were going over the whole ship with a microscope."

 Bigman said, "We have a right to do it. This isLucky Starr!"

 "Hesays he's Lucky Starr. If he's a member of theCouncil of Science, he can prove it and he knows how.If I had any brains, I'd have demanded identificationbefore taking you down."

 113

 114                      

 "It's not too late now," Lucky said calmly. "Canyou see clearly from that distance?" He held up onearm, palm forward, and peeled the sleeve back.

 "I'm not coming any closer," Panner said angrily.

 Lucky said nothing to that. He let his wrist tell thestory. The skin along the inner surface of his wristseemed merely exposed skin, but years before it hadbeen treated hormonally in a most complicated fashion. Responding to nothing more than a disciplined effortof Lucky's will, an oval spot on the wrist darkened and slowly turned black. Within it, little yellow specks formed in the familiar patterns of the Big Dipper andof Orion.

 Panner gasped as though the breath had been forci­bly knocked out of his lungs. Few human beings hadthe occasion to see this sign of the Council, but allabove the age of childhood knew it for what it was— the final and unforgeable identification insigne of the councilman of science.

 Panner was left with no choice. Silently, reluctantly,he released the force field and stepped back.

 Bigman came out, raging, "I ought to bend in your skull, you lopsided—"

 Lucky pulled him back. "Forget it, Bigman. Theman had as much right to suspect us as we had tosuspect him. Settle down."

 Panner shrugged. "It seemed logical."

 "I admit it did. I think we can trust each other now."

 "You, maybe," the chief engineer said pointedly."You're identified. What about this little loudmouthwith you? Who identifies him?"

 Bigman squawked incoherently and Lucky steppedin between the two. "I identify him and take full re­sponsibility for him. . . . Now I propose that we get

                                                                               115

 back to passenger quarters before a search is or­ganized for us. Everything that went on down here is,of course, strictly confidential."

 Then, as though nothing had happened, they re­sumed the climb upward.

 The room assigned to them contained a two-deckerbed and a washstand out of which a small trickle ofwater could be urged. Nothing more. Even the crampedand Spartan quarters on board theShooting Starr wereluxury to this.

 Bigman sat cross-legged on the upper bed, whileLucky sponged his neck and shoulders. They talkedin whispers, conscious of the listening ears that mightbe present on the other side of the walls.

 Bigman said, "Look, Lucky, suppose I go up toeach person on board ship;I mean, each of the ten wedon't know about? Suppose I deliberately pick a fightwith each one, call them a few names, things like that? Wouldn't it turn out that the guy who doesn'ttake a punch at me is the robot?"

 "Not at all. He might not want to break shipboarddiscipline, or he might know what a handy fellow youare with a needle-gun, or he might not want to get intoa wrangle with the Council of Science, or he might Just not like to hit a man smaller than himself."

 "Aw, come on, Lucky." Bigman was silent for a minute, then he said cautiously, ''I've been thinking; how can you besure the robot is aboard ship? I keepthinking maybe it stayed back on Jupiter Nine. It'spossible."

 "I know it's possible and yet I'm sure the robot ishere on board ship. That's just it. Fm sure and I don'tknow why I'm sure," said Lucky, his eyes dark with

 116                      

 thought. He leaned against the bed and tapped histeeth with the knuckle of one finger. "That first daywe landed on Jupiter Nine, something happened."

 "What?"

 "If I only knew! I had it; I knew what it was, orthought I did, just before I went to sleep that night,and it vanished. I haven't been able to get it back. If Iwere on Earth, I'd submit to a psycho-probe. GreatGalaxy, I swear I would!

 ''I've tried every trick I could. Thinking hard, getting my mind off it altogether. When we were with Pannerdown in the engine levels, I tried talking my fool headoff. I thought if I would just keep discussing every as­pect of the matter, the thought was bound to pop intomy head. It didn't.

 "But it's there just the same. It's because of thethought that I must feel so sure the robot is one of the men aboard ship. I've made the subconscious deduc­tion. If I could only put my finger on it, I'd have thewhole answer. If I could only put my finger on it"

 He sounded almost despairing.

 Bigman had never seen Lucky with quite that lookof frustrated loss in his face. He said, worried, "Hey, we'd better get some sleep."

 "Yes, we'd better."

 Minutes later, in the darkness, Bigman whispered,"Hey, Lucky, what makes you so sure I'm not the robot myself?"

 Lucky whispered back, "Because the Sirians couldn'tbear to build a robot with such an ugly face," and lifted his elbow to ward off a flying pillow.

 The days passed. Halfway to Jupiter, they passedthe inner and more sparsely populated belt of small

 117

 moons, of which only Six, Seven, and Ten were num­bered. Jupiter Seven was visible as a bright star, butthe others were far enough away to melt into thebackground of the constellations.

 Jupiter itself had grown to the size of the moonas seen from Earth. And because the ship was ap­proaching the planet with the sun squarely to its rear,Jupiter remained in the "full" phase. Its entire visiblesurface was ablaze with sunlight. There was no shadowof night advancing across it.

 Yet though the size of the moon, it was not so brightas the moon by any means. Its cloud-decked surfacereflected eight times as much of the light that reachedit, as did the bare powdered rock of the moon. Thetrouble was that Jupiter only received one twenty-seventh of the light per square mile that the moon did.The result was that it was only one third as bright atthat moment as the moon appeared to be to human beings on Earth.

 Yet it was more spectacular than the moon. Its beltshad become quite distinct, brownish streaks with softfuzzy edges against a creamy-white background. It waseven easy to make out the flattened straw-coloredoval that was the Great Red Spot as it appeared at one edge, crossed the face of the planet, then disappearedat the other.

 Bigman said, "Hey, Lucky, Jupiter looks as thoughit isn't really round. Is that just an optical illusion?"

 "Not at all," said Lucky. "Jupiterreally isn't round.It's flattened at the poles. You've heard that Earth isflattened at the poles, haven't you?"

 "Sure. But not enough to notice."

 "Of course not. Consider! Earth is twenty-five thou­sand miles about its equator and rotates in twenty-four

 118                      

 hours, so that a spot on its equator moves just over athousand miles an hour. The resulting centrifugal forcebulges the equator outward so that the diameter of theEarth across its middle is about twenty-seven milesmore than the diameter from North Pole to SouthPole. The difference in the two diameters is only abouta third of one per cent so that from space Earth lookslike a perfect sphere."

 "Oh."

 "Now take Jupiter. It is 276,000 miles about itsequator, eleven times the circumference of Earth, yet itrotates about its axis in only ten hours; five minutesless than that, to be exact. A point on its equator ismoving at a speed of almost twenty-eight thousandmiles an hour; or twenty-eight times as fast as anypoint on Earth. There's a great deal more centrifugalforce and a much larger equatorial bulge, especiallysince the material in Jupiter's outer layers is muchlighter than that hi the Earth's crust. Jupiter's diameteracross its equator is nearly six thousand miles morethan its diameter from North Pole to South Pole. Thedifference in the diameters is a full fifteen per cent,and that's an easy thing to see."

 Bigman stared at the flattened circle of light thatwas Jupiter and muttered, "Sands of Mars!"

 The sun remained behind them and unseen as theysank toward Jupiter. They crossed the orbit of Callisto,Jupiter Four, outermost of Jupiter's major satellites,but did not see it to advantage. It was a world one anda half million miles from Jupiter and as large asMercury, but it was on the other side of its orbit, asmall pea close to Jupiter and heading into eclipse in itsshadow.

 119

 Ganymede, which was Jupiter Three, was close enough to show a disc one third as wide as the moonseen from Earth. It lay off to one side so that part of its night surface could be seen. It was three quarters full even so, pale white, and featureless.

 Lucky and Bigman found themselves ignored by therest of the crew. The commander never spoke to themor even looked at them, but moved past with eyesfixed on nothingness. Norrich, when he was led past by Mutt, nodded cheerfully as he always did when hedetected the presence of humans. When Bigman an­ swered the greeting, however, the pleasant look van­ished from his face. A gentle pressure on Mutt's harnessstarted the dog moving and he was gone.

 The two found it more comfortable to eat in theirown quarters.

 Bigman grumbled. "Who in space do they think theyare? Even that guy Panner gets busy all at once whenI'm around."

 Lucky said, "In the first place, Bigman, when thecommander makes it so obvious that we're in his bad books, subordinates don't fall over themselves beingfriendly. Secondly, our dealings with a few of the menhave been unpleasant."

 Bigman said thoughtfully, "I met Red Summers to­day, the cobber. There he was coming out of the engine room and there I was, facing him."

 "What happened? You didn't..."

 "I didn't do anything. I just stood there waiting forhim to start something,hoping he would start some­thing, but he just smiled and moved around me."

 Everyone aboard theJovian Moon was watching theday Ganymede eclipsed Jupiter. It wasn't a true eclipse.

 120                       

 Ganymede covered only a tiny part of Jupiter. Gany­mede was 600,000 miles away, not quite half the sizeof the moon as seen from Earth. Jupiter was twice thedistance, but it was a swollen globe now, fourteen times as wide as Ganymede, menacing and frighten­ing.

 Ganymede met Jupiter a little below the latter'sequator, and slowly the two globes seemed to melt to­gether. Where Ganymede cut in, it made a circle ofdimmer light, for Ganymede had far less of an atmo­sphere than Jupiter had and reflected a considerablysmaller portion of the light it received. Even if that hadnot been so, it would have been visible as it cut acrossJupiter's belts.

 The remarkable part was the crescent of blackness that hugged Ganymede's rear as the satellite movedcompletely onto Jupiter's disk. As the men explained toone another in breathless whispers, it was Ganymede'sshadow falling on Jupiter.

 The shadow, only its edge seen, moved with Gany­mede, but slowly gained on it. The sliver of black cut finer and finer until in the mid-eclipse region, whenJupiter, Ganymede, and theJovian Moon all made astraight line with the sun, the shadow was completelygone, covered by the world that cast it.

 Thereafter, as Ganymede continued to move on, the shadow began to advance, appearing before it,first a sliver, then a thicker crescent, until both left Jupiter's globe.

 The entire eclipse lasted three hours.

 TheJovian Moon reached and passed the orbit ofGanymede when that satellite was at the other end ofits seven-day orbit about Jupiter.

 121

 There was a special celebration when that hap­pened. Men with ordinary ships (not often, to be sure)had reached Ganymede and landed on it, but no one,not one human being, had ever penetrated closer thanthat to Jupiter. And now theJovian Moon did.

 The ship passed within one hundred thousand miles of Europa, Jupiter Two. It was the smallest of Jupiter's major satellites, only nineteen hundred miles in diam­eter. It was slightly smaller than the moon, but its close­ness made it appear twice the size of the moon asseen from Earth. Dark markings could be made outthat might have been mountain ranges. Ship's tele­scopes proved they were exactly that. The mountainsresembled those on Mercury, and there was no signof moon-like craters. There were brilliant patches, too,resembling ice fields.

 And still they sank downward, and left Europa'sorbit behind.

 Io was the innermost of Jupiter's major satellites, in size almost exactly equal to Earth's moon. Its distancefrom Jupiter, moreover, was only 285,000 miles, orlittle more than that of the moon from Earth.

 But there the kinship ended. Whereas Earth's gentle gravitational field moved the moon about itself in thespace of four weeks, Io, caught in Jupiter's gravity, whipped about in its slightly larger orbit in the spaceof forty-two hours. Where the moon moved about Earthat a speed of a trifle over a thousand miles an hour, Iomoved about Jupiter at a speed of twenty-two thousandmiles an hour, and a landing upon it was that muchmore difficult.

 The ship, however, maneuvered perfectly. It cut inahead of Io and wiped out Agrav at just the propermoment.

 122                       

 With a bound, the hum of the hyperatomics wasback, filling the ship with what seemed a cascade ofsound after the silence of the past weeks.

 TheJovian Moon curved out of its path, finally,subject once again to the accelerating effect of a gravi­tational field, that of lo. It was established in an orbitabout the satellite at a distance of less than ten thou­sand miles, so that lo's globe filled the sky.

 They circled about it from dayside to nightside,coming lower and lower. The ship's batlike Agrav finswere retracted in order that they might not be tornoff by Io's thin atmosphere.

 Then, eventually, there was the keen whistling thatcame with the friction of ship against the outermost wisps of that atmosphere.

 Velocity dropped and dropped; so did altitude. Theship's sidejets curved it to face stern-downward toward Io, and the hyperatomic jets sprang into life, cushion­ing the fall. Finally, with one last bit of drop and the softest jar, theJovian Moon came to rest on the sur­face of Io.

 There was wild hysteria on board theJovian Moon. Even Lucky and Bigman had their backs pounded by men who had been avoiding them constantly all voy­age long.

 One hour later, in the darkness of Io's night, withCommander Donahue in the lead, the men of theJovian Moon,each in his space suit, emerged one by one onto the surface of Jupiter One.

 Sixteen men. The first human beings ever to land on Io!

 Correction, thought Lucky. Fifteen men.

 And one robot!

 12

 The Skies and Snows of Io

 It was Jupiter they stopped to look at. It was Jupiterthat held them frozen. There was no talk about it,no babble over the helmet radios. It was beyond talk.

 Jupiter was a giant globe which, from rim to rim,extended one eighth of the way across the visible sky.Had it been full, it would have been two thousandtimes as bright as the Earth's full moon, but the night shadow cut a third of it away.

 The bright zones and dark belts that crossed it werenot merely brown now. They were close enough to showfull clear color: pink, green, blue, and purple, amaz­ingly bright. The edges of the bands were ragged andslowly changed shape as they watched, as though theatmosphere were being whipped into gigantic and tur­bulent storms, as most probably it was. Io's clear, thin atmosphere didn't obscure the smallest detail of thatcolored shifting surface.

 The Great Red Spot was heaving ponderously intosight. It gave the impression of a funnel of gas, swirlinglazily.

 They watched for a long time, and Jupiter did not

 123

 124                      

 change position. The stars moved past it, but Jupiterremained fixed where it was, low in the western sky. It could not move, since Io presented only one side to Jupiter as it revolved. On nearly half of Io's surfaceJupiter never rose, and on nearly half it never set. Inan in-between region of the satellite, a region making up nearly a fifth of the total surface, Jupiter remainedforever on the horizon, part showing, part hidden.

 "What a place for a telescope!" murmured Bigmanon the wave length allotted to Lucky during the pre-landing briefing.

 Lucky said, "They'll have one soon and a lot of otherequipment."

 Bigman touched Lucky's face-plate to attract his at­tention and pointed quickly. "Look at Norrich. Poor guy, he can't see any of this!"

 Lucky said, "I noticed him before. He's got Muttwith him."

 "Yes. Sands of Mars, they go to trouble for thatNorrich! That dog suit is a special job. I was watching them put it on the dog when you were keeping tabs onthe landing. They had to test to make sure he couldhear the orders and obey them and if he'd let Norrichuse him once Norrich got into a space suit. Apparentlyit all worked out."

 Lucky nodded. On impulse he moved rapidly in Norrich's direction. Io's gravity was just a trifle overthat of the moon, and both he and Bigman couldhandle that neatly.

 A few long, flat strides did the job. "Norrich," saidLucky, shifting to the engineer's wave length.

 One cannot tell direction of a sound when it comes

 125

 out of earphones, of course, and Norrich's blind eyeslooked about helplessly. "Who is it?"

 "Lucky Starr." He was facing the blind man, andthrough the face-plate could make out clearly the lookof intense joy on Norrich's face. "You're happy to behere?"

 "Happy? You might call it that. Is Jupiter verybeautiful?"

 "Very. Would you want me to describe it to you?"

 "No. You don't have to. I've seen it by telescopewhen—when I had eyes, and I can see it in my mindnow. It's just that... I don't know if I can make youunderstand. We're some of the few people to stand on anew world for the first time. Do you realize what aspecial group that makes us?"

 His hand reached down to stroke Mutt's head andcontacted only the metal of the dog's helmet, of course.Through the curved face-plate, Lucky could see thedog's lolling tongue, and his uneasy eyes turning rest­lessly this way and that, as though disturbed by thestrange surroundings or by the presence of his master'svoice without the familiar body that went with it.

 Norrich said quietly, "Poor Mutt! The low gravityhas him all confused. I won't keep him out muchlonger."

 Then, with an increase of passion again, "Think ofall the trillions of people in the galaxy. Think how fewof them have had the luck to be the first on a world.You can almost name them all off. Janofski and Ster­ling were the first men on the moon, Ching the firstman on Mars, Lubell and Smith on Venus. Add them all up. Even count in all the asteroids and all the plan-

 126                       

 ets outside the solar system. Add up all the firsts andsee how few there are. And we're among those few.I'm among those few."

 He flung his arms out as though he were ready toembrace the whole satellite. "And I owe that to Sum­mers, too. When he worked out a new technique formanufacturing the lead contact point—it was just a matter of a bent rotor, but it saved two million dollars and a year's time, and he not even a trained mechanic—they offered to let him be in the party as reward. You know what he said. He said I deserved it in hisplace. They said sure, but I was blind, and he remindedthem why I was blind and said he wouldn't go withoutme. So they took us both. I know you two don't think much of Summers, but that's what I think of whenIthink of him."

 The commander's voice sounded ringingly in allhelmets: "Let's get to work, men. Jupiter will staywhere it is. Look at it later."

 For hours the ship was unloaded, equipment was setup, tents unfurled. Temporary air tights were prepared for possible use as oxygen-supplied headquarters out­side the ship.

 The men were not to be kept from watching theunusual sky, though. As it happened, all three of Jupi­ter's other large satellites were in the sky.

 Europa was closest, appearing somewhat smaller than Earth's moon. It was a crescent, near the easternhorizon. Ganymede, appearing smaller still, was nearerzenith and half full. Callisto, only a quarter the widthof Earth's moon, was nudging close to Jupiter and,

                                                                               127

 like Jupiter, was some two thirds full. All three to­gether gave not one quarter the light of Earth's fullmoon and were completely inconspicuous in the pres­ence of Jupiter.

 Bigman said exactly that.

 Lucky looked down at his small Martian friendafter having studied the eastern horizon thoughtfully."You think nothing could beat Jupiter, do you?"

 "Not out here," Bigman said stoutly.

 ''Then keep watching," said Lucky.

 In Io's thin atmosphere there was no twilight tospeak of and no warning. There was a diamondlikesparkle along the frost-covered top-line of the ridge oflow hills, and seven seconds later the sun had topped the horizon.

 It was a tiny seed-pearl of a sun, a little circle ofbrilliant white, and for all the light that giant Jupiter cast, the pigmy sun cast much, much more.

 They got the telescope up in time to catch Callisto vanishing behind Jupiter. One by one, all three satel­lites would do the same. Io, although it kept only oneface to Jupiter, revolved about it in forty-two hours.That meant that the sun and all the stars seemed tomarch around Io's skies in those forty-two hours.

 As for the satellites, Io moved faster than any of them, so it kept overtaking them in the race aboutJupiter. It overtook the farthest and slowest, Callisto,most rapidly; so Callisto circled Io's heavens in twodays. Ganymede took four days and Europa seven.Each traveled from east to west and each in due turnwas to pass behind Jupiter.

 128                      

 The excitement in the case of the Callisto eclipse,which was the first to be witnessed, was extreme. EvenMutt seemed to be affected by it. He had grown in­ creasingly used to low gravity, and Norrich gave himperiods of freedom during which he floundered gro­ tesquely about and tried vainly to inspect by nose thenumerous strange things he encountered. And in theend, when Callisto reached Jupiter's glowing curve and passed behind, and all the men grew silent, Mutt, too,sat on his swathed haunches and, tongue lolling, staredupward at the sky.

 But it was the sun they were really waiting for. Itsapparent motion was faster than that of any of thesatellites. It gained on Europa (whose crescent thinnedto nothingness) and passed behind it, remaining ineclipse for something less than thirty seconds. It emerged, and then Europa was a crescent again, withits horns facing in the other direction now.

 Ganymede had plunged behind Jupiter before thesun could reach it, and Callisto, having emerged frombehind Jupiter, was below the horizon.

 It was the sun and Jupiter now, those two.

 The men watched greedily as the seed-pearl sunclimbed higher in the sky. As it did, Jupiter's phasegrew narrower, its lighted portion always, of course,facing the sun. Jupiter became a "half-moon," then afat crescent, then a thin one.

 In Io's thin atmosphere the sunlit sky was a deeppurple, and only the dimmer stars had been blottedout. Against that background there burnt the giganticcrescent in the sky, bulging out toward the relentlesslyapproaching sun.

 129

 It was like David's pebble hurled from some cosmicslingshot toward Goliath's forehead.

 The light of Jupiter shrank still further and becamea yellowish curved thread. The sun was almost touch­ing.

 It did touch and the men cheered. They had maskedtheir face-plates in order to watch, but now that wasno longer necessary, for the light had dimmed to bear­able dimensions.

 Yet it had not vanished entirely. The sun had movedbehind the edge of Jupiter but it still shone murkilythrough that giant planet's thick, deep atmosphere ofhydrogen and helium.

 Jupiter itself was now completely blanked out, butits atmosphere had sprung to life, refracting and bend­ing the sunlight through itself and around the curveof the planet, a smoothly bending film of milky light.

 The film of light spread as the sun moved farther behind Jupiter. It curved back on itself until faintly, very faintly, the two horns of light met on Jupiter'sother side. Jupiter's vanished body was outlined in light and one side bulged with it. It was a diamondring in the sky, big enough to hold two thousandglobes the size of the moon as seen from Earth.

 And still the sun moved farther behind Jupiter sothat the light began to fade and grow dim, and dimmer,until finally it was gone and, except for the pale cres­cent of Europa, the sky was black and belonged to thestars.

 "It will stay like this five hours," said Lucky to Big-man. "Then everything will repeat itself in reverse asthe sun comes out"

 130                      

 "And this happens every forty-two hours?" said Big-man, awed.''That's right," said Lucky.

 Panner approached them the next day and calledout to them, "How are you? We're almost done here."He spread his arm about in a broad circle to indicatethe loan valley, now littered with equipment. "We'll beleaving soon, you know, and we'll leave most of thisstuff here."

 "We will?" said Bigman, surprised.

 "Why not? There's nothing living on the satellite to disturb the stuff and there's no weather to speak of.Everything's coated for protection against the ammoniain the atmosphere and it will keep nicely till a secondexpedition comes round." His voice was suddenly lower. "Is there anyone else on your private wave length, Councilman?"

 "My receivers don't detect anyone."

 "Do you want to take a walk with me?" He headedout, out of the shallow valley and up the gentle slopeof the surrounding hills. The other two followed.

 Panner said, "I must ask your pardon if I seemed unfriendly on board ship. I thought it better so."

 "There are no hard feelings," Lucky assured him.

 "I thought I'd try an investigation of my own, you see, and I thought it safer not to seem hand in glovewith you. I was sure that if I only watched carefully,I would catch someone giving himself away, doingsomething non-human, if you know what I mean. I failed, I'm afraid."

 They had reached the top of the first rise and Panner

 131

 looked back. He said with amusement, "Look at thatdog, will you? He's getting the real feel of low gravity."

 Mutt had learned a lot in the past few days. His bodyarched and straightened as he lunged in low, twenty-foot leaps, and he seemed to indulge in them for thesheerest pleasure.

 Panner switched Ms radio to the wave length thathad been reserved for Norrich's use in calling Muttand shouted, "Hey, Mutt, hey, boy, come, Mutt," andwhistled.

 The dog heard, of course, and bounded high in theair. Lucky switched to the dog's wave length and heardMs delighted barking.

 Panner waved Ms arm and the dog headed towardthem, then stopped and looked back as though won­dering if he did right to leave his master. He ap­ proached more slowly.

 The men walked onward again. Lucky said, "ASirian robot built to fool a man would be a thoroughjob. Casual examination wouldn't detect the fraud."

 "Mine wasn't casual examination," protested Pan-ner.

 Lucky's voice held more than a tinge of bitterness.''I'm beginning to think that the examination by anyonebut an experienced robotics man can be nothingbutcasual."

 They were passing over a drift of snowlike material,glittering in Jupiter light, and Bigman looked downupon it in amazement.

 "This thing melts if you look at it," he said. Hepicked some up in his gauntleted hand, and it melteddown and ran off like butter on a stove. He looked

 132                       

 back, and where the three had stepped were deep in­dentations.

 Lucky said, "It's not snow, it's frozen ammonia,Bigman. Ammonia melts at a temperature eighty de­grees lower than ice does, and the heat radiating fromour suits melts it that much faster."

 Bigman lunged forward to where the drifts laydeeper, gouging holes wherever he stepped, andshouted, "This is fun."

 Lucky called, "Make sure your heater is on if you'regoing to play in the snow."

 "It's on," yelled Bigman, and running down a ridgewith long low leaps, he flung himself headlong into abank. He moved like a diver in slow motion, hit the drifted ammonia, and, for a moment, disappeared. Hefloundered to his feet.

 "It's like diving into a cloud, Lucky. You hear me?Come on, try it. More fun than sand skiing on themoon."

 "Later, Bigman," Lucky said. Then he turned to Panner. "For instance, did you try in any way to test any of the men?"

 Out of the corner of his eye Lucky could see Bigmanplunging into a bank for a second time, and, after afew moments had elapsed, his eyes turned full in thatdirection. Another moment and he called out anx­iously, "Bigman!" Then, more loudly and much more anxiously,"Bigman!"

 He started running.

 Bigman's voice came, weak and gasping. "Breath...knocked out...hit rock ... river down here . .."

 "Hold on,I'll be with you." Lucky and Panner, too,were devouring space with their strides.

 133

 Lucky knew what had happened, of course. Thesurface temperature of Io was not far removed fromthe melting point of ammonia. Underneath the am­ monia drifts, melting ammonia couldbe feeding hid­den rivers of that foul-smelling, choking substancethat existed so copiously on the outer planets and theirsatellites.

 There was the rattle of Bigman's coughing in hisear. "Break in air hose . . . ammonia getting in . . .choking."

 Lucky reached the hole left by Bigman's divingbody and looked down. The ammonia river was plainlyvisible, bubbling slowly downhill over sharp crags. Itmust have been against one of those that Bigman'sair hose had been damaged.

 "Where are you, Bigman?"

 And though Bigman answered feebly, "Here," hewas nowhere to be seen.

 13

 Fall!

 Lucky jumped recklessly into the exposed river, drift­ing gently downward under the pull of Io's weakgravity. He was angry at the slowness of his fall, atBigman for the childish enthusiasms that seized him so suddenly, and—unpredictably—at himself for not hav­ing stopped Bigman when he might.

 Lucky hit the stream, and ammonia sprayed highin the air, then fell back with surprising quickness. Io's thin atmosphere could not support the smalldroplets even at low gravity.

 There was no sense of buoyancy to the ammoniariver. Lucky had not expected any to speak of. Liquidammonia was less dense than water and had less liftingpower. Nor was the force of the current great under I o's weak pull. Had Bigman not damaged his air hose,it would have been only a matter of walking out of the river and through any of the drifts that might havepacked it round.

 As it was . . .

 Lucky splashed downstream furiously. Somewhereahead the small Martian must be struggling feebly

 135

 136                       

 against the poisonous ammonia. If the break in thehose was large enough, or had grown large enough, toallow liquid ammonia to enter, Lucky would be toolate.

 He might be too late, already, and his chest con­stricted and tightened at the thought.

 A form streaked past Lucky, burying itself in thepowdered ammonia. It disappeared, leaving a tunnelinto which ammonia slowly collapsed.

 "Panner," Lucky said tentatively.

 "Here I am." The engineer's arm fell upon Lucky'sshoulder from behind. "That was Mutt. He came run­ning when you yelled. We were both on his wavelength."

 Together they forged through the ammonia on thetrack of the dog. They met him, returning.

 Lucky cried eagerly, "He's got Bigman."

 Bigman's arms feebly enfolded the dog's suit-encased haunches, and though that hampered Mutt'smovements, low gravity enabled the dog to makerespectable headway through use of shoulder musclesalone.

 Even as Lucky bent for Bigman, the little Martian'sstraining hold relaxed and he fell.

 Lucky scooped him up. He wasted no time on in­vestigation or talk. There was only one thing to do.He turned up Bigman's oxygen flow to full capacity,slung him over his shoulders, and ran for the ship.Even allowing for Io's gravity he had never run sorecklessly in his life. With such haste did he kick the ground away when coming down from each hurtling,horizontal stride that the effect was almost one oflow-level flying.

 137

 Panner pumped along in the rear, and Mutt stayedexcitedly at Lucky's heels.

 Lucky used the communal wave length to alert theothers even as he was running and one of the airtights was made ready.

 Lucky hurtled inside the air tight, scarcely breaking his stride. The flap closed behind him and the interior flooded with additional air under pressure to make upthe loss during the flap's opening.

 With flying fingers he unbuckled Bigman's helmet,then more slowly drew off the rest of the suit.

 He felt for the heartbeat and, to his relief, found it.The air tight was equipped, of course, with a first-aidkit. He made the necessary injections for general stim­ulation and waited for warmth and plentiful oxygento do the rest.

 And eventually Bigman's eyes fluttered and focusedwith difficulty on Lucky. His lips moved and made theword "Lucky," though no sound was involved.

 Lucky laughed with relief and finally took thetime to remove his own space suit.

 On board theJovian Moon Harry Norrich stoppedat the open door of the compartment within which Big-man was completing his recuperation. His unseeing,china-blue eyes were warm with pleasure.

 "How's the invalid?"

 Bigman struggled up in his bunk and shouted,"Fine! Sands of Mars, I feel great! If it weren't thatLucky wants to keep me down, I'd be up and around."

 Lucky grunted his disbelief.

 Bigman ignored that. He said, "Hey, let Mutt comein. Good old Mutt! Here, boy, here!"

 Mutt, the hold on his harness released, trotted over

 138                      

 to Bigman, his tail wagging furiously and his intelligenteyes doing everything but talk a greeting.

 Bigman's small arm embraced the dog's neck in abear hug. "Boy,there's a friend. You heard what hedid, Norrich, didn't you?"

 "Everyone did," and it was plain to see that Norrichtook a great personal pride in his dog's accomplish­ment.

 "I just barely remember it," Bigman said, "before I blacked out altogether. I got that lungful of ammonia and couldn't seem to straighten out. I rolled downhill,just going through the ammonia snow as though itwere nothing. Then there was this thing coming at meand I was sure it was Lucky when I heard the sound ofsomething moving. But he knocked enough of the snow off us to let some of the Jupiter light come inand I could just make out it was Mutt. The last thing I remember was grabbing him."

 "And a good thing, too," Lucky said. "The extratime that would have been required for me to find youwould have been your finish."

 Bigman shrugged. "Aw, Lucky, you make such abig deal out of it. Nothing would have happened if Ihadn't just caught the hose on a rock and torn it. Atthat if I had had enough brains to turn up my oxygenpressure, I could have kept the ammonia out. It wasjust the first lungful that seemed to put me out ofkilter. I couldn't think."

 Panner passed by, just then, and looked. "How areyou, Bigman?"

 "Sands of Mars! Looks like everyone thinks I'm aninvalid or something. There's nothing wrong with me.

 .                                                                             139

 Even the commander stopped by and managed to findhis tongue long enough to grunt at me."

 "Well," said Panner, "maybe he's getting over his mad."

 "Never," said Bigman. "He just wants to make surehis first flight won't be spoiled by a casualty. He wantshis record pure white, that's all."

 Panner laughed. "All set for the take-off?"

 Lucky said, "Are we leaving Io?"

 "Any hour. The men are reloading the equipmentwe're taking with us and securing what we leave be­hind. If you two can make the pilot room once we'reunderway, do so. We'll get a better look at Jupiterthan ever."

 He tickled Mutt behind one ear and left

 They radioed Jupiter Nine that they were leaving Io, as days earlier they had radioed that they had sur­faced on the satellite.

 Bigman said, "Why don't we call Earth? ChiefCouncilman Conway ought to know we've made it."

 "Officially," said Lucky, "we haven't made it all theway until we've returned to Jupiter Nine."

 He did not add aloud that he was not at all anxiousto return to Jupiter Nine, still less anxious to talk to Conway. He had, after all, accomplished nothing on this trip,

 His brown eyes surveyed the control room. The en­gineers and crewmen were at their stations for thetakeoff. The commander, his two officers and Panner,however, were in the control room.

 Lucky wondered again about the officers as timeand again he had wondered about each of the ten menwhom the V-frog had not had a chance to eliminate.

 140                      

 He had spoken to each of them on occasion, as had Panner even more frequently. He had searched thek quarters. He and Panner together had gone over thekrecords. Nothing had resulted.

 He would be going back to Jupiter Nine with therobot unlocated, and thereafter location would beharder than ever and he might have to report back to Council headquarters with news of failure.

 Once more, desperately, the thought of X rays en­tered his mind, or some other means of forceful inspec­tion. As always, he thought at once of the possibilityof triggering off an explosion, probably a nuclear ex­plosion.

 It would destroy the robot. It would also kill thir-teen men and blow up a priceless ship. Worst of all,it would show no safe way of detecting the humanoidrobots which, Lucky felt certain, were preying inother parts of the Solar Confederation.

 He was startled by Panner's sudden cry, "Here wego!"

 There was the familiar distantwhoosh of the initial thrust, the gathering backward press of accelerations,and Io's surface dropped away, faster and faster.

 The visiplate could not center Jupiter in its entirety:"it was too large. It centered the Great Red Spot insteadand followed it in its rotation about the globe.

 Panner said, "We've gone into Agrav again, yes, butit's only temporary, just to let Io pull away from us."

 "But we're still falling toward Jupiter," Bigmansaid.

 "That's right, but only till the proper moment isreached. Then we go into hyperatoroic drive and

 141

 plunge toward Jupiter on a hyperbolic orbit. Once thatis established, we cut the drive and let Jupiter do thework. Our closest approach will be about 150,000miles. Jupiter's gravity will zoom us around as thoughwe were a pebble in a slingshot and shoot us out again.At the proper point our hyperatomic drive cuts inagain. By taking advantage of the slingshot effect, weactually save a bit on energy over the alternative ofleaving directly from Io,and we get some super close-ups of Jupiter."

 He looked at his watch. "Five minutes," he said.

 He was referring, as Lucky knew, to the momentwhen the ship would switch from Agrav to hyper-atomic drive and begin to curve off into the plannedorbit about Jupiter.

 Still staring at his watch, Panner said, "The timeis selected so that we come out heading toward JupiterNine as squarely as possible. The fewer side adjust­ments we have to make, the more energy we save.We've got to come back to Jupiter Nine with as muchof our original energy store as possible. The more wecome back with, the better Agrav looks. I've set mygoals at eighty-five per cent. If we can come backwith ninety, that would be superlative."

 Bigman said, "Suppose you come back with moreenergy than you had when you left? How would thatbe?"

 "Super-superlative, Bigman, but impossible. There'ssomething called the second law of thermodynamicsthat stands in the way of making a profit on the dealor, for that matter, of breaking even. We've got to takesome loss." He smiled broadly and said, "One minute."

 And at the appropriate second the sound of the

 142                      

 hyperatomics filled the ship with its muted murmurings,and Panner placed his watch in his pocket with asatisfied expression.

 "From here on in," he said, "until actual landingmaneuvers at the Jupiter Nine approach, everythingis quite automatic."

 He had no sooner said that when the hummingceased again, the lights in the room flickered and wentout. Almost at once they went on again, but nowthere was a little red sign on the control panel that said,emergency.

 Panner sprang to his feet. "What in Space .. .?''

 He left the pilot room at a run, leaving the othersstaring after him and at one another in various degreesof horror. The commander had gone dead-white, Mslined face a tired mask.

 Lucky, with sudden decision, followed Panner, and Bigman, of course, followed Lucky.

 They came upon one of the engineers clamberingout of the engine compartment. He was panting. "Sir!"

 "What is it, man?" snapped Panner.    "The Agrav is off, sir. It can't be activated."

 "What about the hyperatomics?"

 "The main reserve is shorted. We cut it just in timeto keep it from blowing. If we touch it, the wholeship will go up. Every bit of the stored energy willblow."

 ''Then we're working on the emergency reservoir?"

 ''That's right."

 Panner's swarthy face was congested with blood."What good is that? We can't set up an orbit aboutJupiter with the emergency reservoir. Out of the way.Let me down there."

 143

 The engineer stepped aside, and Panner swung intothe shaft. Lucky and Bigman were at his heels.

 Lucky and Bigman had not been in the engine com­partment since that first day aboard theJovian Moon.The scene was different now. There was no augustsilence, no sensation of mighty forces quietly at work.

 Instead, the puny sound of men rose high aboutthem.

 Panner sprang off into the third level. "Now what'swrong?" he called. "Exactly what's wrong?"

 Men parted to let him through and they all huddledover the gutted insides of a complex mechanism, point­ing things out in tones of mingled despair and anger.

 There were sounds of other footsteps coming downthe rungs of the shaft, and then the Commander him­self made his appearance.

 He spoke to Lucky, who was standing gravely to oneside. "What is it, Councilman?" It was the first timehe had addressed Lucky since they had left JupiterNine.

 Lucky said, "Serious damage of some sort, Com­mander."

 "How did it happen?Panner!"

 Panner looked up from the close examination of something that had been held out to him. He shoutedin annoyance, "What in space do you want?"

 Commander Donahue's nostrils flared. "Why hassomething been allowed to go wrong?"

 "Nothing has beenallowed to go wrong."

 "Then what do you call this?"

 "Sabotage, Commander. Deliberate, murdering sab­otage!"

 "What!"

 144                      

 "Five gravitic relays have been completely smashedand the necessary replacements have been removed and can't be located. The hyperatomic thrust-controlhas been fused and shorted beyond repair. None of ithappened by accident."

 The commander stared at his chief engineer. Hesaid, hollowly, "Can anything be done?"

 "Maybe the five relay replacements can be locatedor cannibalized out of the rest of the ship. I'm not sure.Maybe a makeshift thrust-control can be set up. Itwould take days anyway and I couldn't guarantee re­sults."

 "Days!" cried the commander. "It can't take days.We're fatting toward Jupiter!"

 There was a complete silence for a few moments,and then Panner put into words what all of them knew."That's right, Commander. We're failing toward Jupi­ter and we can't stop ourselves in time. It means we'rethrough, Commander. We're all dead men!"

 14

 Jupiter Close Up

 It was Lucky who broke the deadly silence that fol­lowed, in sharp, incisive tones. "No man is dead whilehe has a mind capable of thought. Who can handlethis ship's computer most rapidly?"

 Commander Donahue said, "Major Brant. He's theregular trajectory man."

 "Is he up in the control room?"

 "Yes."

 "Let's get to him. I want the detailedPlanetaryEphemerae. . . Panner, you stay here with the menand get to work cannibalizing and improvising."

 "What good will it—?" Panner began.

 Lucky cut in at once. "Perhaps no good at all. Ifso, we'll hit Jupiter and you'll die after having wasteda few hours of labor. Now I've given you an order.Get to work!"

 "But..." Commander Donahue seemed stuck afterthat one word.

 Lucky said, "As councilman of science, I'm assum­ing command of this vessel. If you wish to disputethat, I'll have Bigman lock you in your cabin and you

 145

 146                       

 can argue it out at the court-martial proceedings, as­suming we survive."

 Lucky turned away and moved quickly up the cen­tral shaft. Bigman motioned Commander Donahueup with a quick jerk of his thumb and followed last.

 Panner looked after them scowling, turned savagelyto the engineers,and said, "All right, you bunch ofcorpses. No use waiting for it with our fingers inour mouths. Hop to it."

 Lucky strode into the control room.

 The officer at the controls said, "What's wrongdown there?" His lips were white.

 "You're Major Brant," said Lucky, "We haven'tbeen formally introduced, but never mind that. I'mCouncilman David Starr, and you're taking orders from me. Get at that computer and do what you'retold with all the speed you have."

 Lucky had thePlanetary Ephemerae before him.Like all great reference works, it was in book formrather than film. The turning of pages, after all, madefor the more rapid location of a specific piece of in­formation, than did the long-drawn-out unwinding offilm from end to end.

 He turned the pages now with practiced hand,searching among the rows and columns of numbersthat located the position of every chunk of matter inthe solar system over ten miles in diameter (and someunder) at certain standard tunes, together with theirplanes of revolution and velocity of motion.

 Lucky said, "Take the following co-ordinates as Icall them out, together with the line of motion, andcalculate the characteristics of the orbit and the posi-

 147

 tion of the point at this moment and for succeeding moments for the space of forty-eight hours."

 The major's fingers flew as figures were converted by the special punch machine into a coded tape whichwas fed into the computer.

 Even while that was taking place, Lucky said, "Cal­culate from our present position and velocity our orbitwith respect to Jupiter and the point of intersectionwith the object whose orbit you have just calculated."

 Again the major worked.

 The computer spat out its results in coded tape thatwound on to a spool and dictated the tapping of atypewriter that spelled out the results in figures.

 Lucky said, "At the point of intersection, what istime discrepancy between our ship and the object?"

 Again the major worked. He said, "We miss it byfour hours, twenty-one minutes, and forty-four sec­onds."

 "Calculate how the velocity of the ship must be al­tered in order to hit the point squarely. Use one hour from now as the starting time."

 Commander Donahue broke in. "We can't doanything this close to Jupiter, Councilman. The emer­gency power won't break us away. Don't you under­stand that?"

 "I'm not asking the major to break us away, Com­mander. I'm asking him to accelerate the ship toward Jupiter, for whatever our reserve power is worth."

 The commander rocked back on his heels."TowardJupiter?"

 The computer was making the calculation and theresults were coming in. Lucky said, "Can you accel­erate by that much on the power available?"

 148                      .

 Major Brant said shakily, "I think so."

 "Then do it."

 Commander Donahue said again,"Toward Jupiter?"

 "Yes. Exactly. Io isn't the innermost of Jupiter'ssatellites. Amalthea is closer, Jupiter Five. If we canintersect its orbit properly, we can land on it. If wemiss it, well, then, we will have hurried death by twohours."

 Bigman felt a surge of sudden hope. He could neverentirely despair while Lucky was in action, but untilthat moment he had not seen what it was that Lucky intended doing. He remembered now his earlier con­versation with Lucky on the subject. The satellites werenumbered in order of discovery. Amalthea was a smallsatellite, just a hundred miles in diameter, and it was discovered only after the four major satellites wereknown. So, though the closest to Jupiter, it was JupiterFive. Somehow one tended to forget that. Because Iowas called Jupiter One, there was always the tendencyto think there was nothing between it and the planetitself.

 And one hour later theJovian Moon began a care­fully plotted acceleration toward Jupiter, hasteningtoward the death trap.

 They no longer centered the visiplate on any part ofJupiter. Though the latter swelled hourly, the centerof sight remained on a portion of the star field a con­siderable distance from Jupiter's rim. The star field was under maximum magnification. At that pointshould be Jupiter Five, streaking for its rendezvouswith a ship which was hurtling and straining down, down toward Jupiter. Either the ship would be caught

                                                                               149

 by the speck of rock and saved, or it would miss and belost forever.

 "There it is," said Bigman in excitement. "That starshows a visible disk."

 "Calculate observed position and motion," orderedLucky, "and check with the computed orbit."

 This was done.

 "Any correction?" Lucky asked.

 ''We'll have to slow down by—"

 ''Never mind the figures. Do it!"

 Jupiter Five circled Jupiter in twelve hours, movingin its orbit at a speed of nearly three thousand miles anhour. This was one and a half times as rapid as Io'smotion and its gravitational field was only one twenti­eth that of Io. For both reasons, it made the hardertarget.

 Major Brant's fists trembled on the controls as theall-important side thrusts bent theJovian Moon's orbitever so slightly to meet the onrushing Jupiter Five, slipbehind it and round, matching speeds for just thosevital moments that would enable the satellite's gravityto establish the ship in an orbit about itself.

 Jupiter Five was a large, brilliant object now. If itstayed so, good. If it began to grow smaller, they hadmissed.

 Major Brant whispered, "We've made it," and bishead fell forward into his shaking palms as he releasedthe controls.

 Even Lucky closed his eyes momentarily in a landof weary relief.

 In one way the situation on Jupiter Five was far dif­ferent from what it had been on Io. There, all the crew

 150                             

 had been sight-seers; the consideration of the heavenshad taken precedence over the leisurely preparations inthe valley.

 Here on Jupiter Five, however, no one emergedfrom theJovian Moon. What there was to see, no onesaw.

 The men stayed aboard the ship and worked on therepair of the engines. Nothing else mattered. If theyfailed, the landing on Jupiter Five could only postponedoom and stretch it out into greater agony.

 No normal ship could land on Jupiter Five to rescue them, and no other Agrav ship existed or would existfor a year at least. If they failed, there would be timeenough to watch Jupiter and the vision of the skieswhile they waited for death.

 Yet under less urgent conditions the vision wouldhave been worth watching. It was Io all over againwith everything doubled and tripled.

 From the point at which theJovian Moon landed,Jupiter's lower rim seemed to sweep the flat, powderyhorizon. The giant looked so close in the airlessnessthat a watcher would have imagined he could reach out his hand and bury it in that circle of light.

 From the horizon Jupiter stretched upward, half­way to zenith. At the moment theJovian Moon landed,Jupiter was almost full, and within the unbearablecircle of brilliant stripes and colors nearly ten thou­sand full moons Earth variety, could have been placed.Almost one sixteenth of the entire vault of the skywas covered by Jupiter.

 And because Jupiter Five circled Jupiter in twelvehours, the visible moons—there were four here ratherthan three as on Io, since Io itself was now a moon—

 151

 moved three times as fast as they did on Io. So didall the stars and everything else in the sky, except forfrozen Jupiter, which one side of the satellite eternallyfaced and which therefore never moved.

 In five hours the sun would rise and it would beexactly the same in appearance as on Io; it would be the one thing that hadn't changed. But it would racetoward a four-times-as-large Jupiter at three times thespeed and make an eclipse a hundred times as terri-fyingly beautiful.

 But no one saw it. It took place twice while theJovian Moonstayed and no one saw it No one hadthe time. No one had the heart

 Panner finally sat down and stared out of blearyeyes. The flesh around them was red and puffy. His voice was a hoarse whisper.

 "All right. Everyone to your normal stations. We'llhave a dry run." He hadn't slept in forty hours. Theothers had worked in shifts, but Panner had stoppedneither to eat nor to sleep.

 Bigman, who had confined himself to unskilledlabor, to fetching and carrying, to reading dials underdirection and holding levers according to instruction, had no place in a dry run, no station, no duties. So he wandered somberly about the ship in search of Luckyand found him in the control room with CommanderDonahue.

 Lucky had his shirt off and was wiping his shoulders,forearms, and face on a large plastofluff towel.

 As soon as he saw Bigman, he said briskly, "Theship will be moving, Bigman. We'll be taking off soon."

 152                      

 Bigman's eyes raised. "We're only doing a dry run, Lucky."

 "It will work. That Jim Panner worked miracles."

 Commander Donahue said stiffly, "CouncilmanStarr, you have saved my ship."

 "No, no. Panner deserves the credit. I think halfthe engine is being held together with copper wire andmucilage, but it will work."

 "You know what I mean, Councilman. You droveus on to Jupiter Five when the rest of us were readyto give up and panic. You saved my ship, and I willreport that fact fully when I stand court-martial onEarth for having failed to co-operate with you on Jupiter Nine."

 Lucky flushed in embarrassment. "I can't allow that,Commander. It is important that councilmen avoid publicity. As far as the official record is concerned,you will have remained in command at all times.There will be no mention of any actions of mine."

 "Impossible. I couldn't allow myself to be praisedfor what you have done."

 "You will have to. It's an order. And let's have notalk of court-martials."

 Commander Donahue drew himself up with a kind of pride. "I deserve court-martial. You warned me ofthe presence of Sirian agents. I did not listen and as a result my ship was sabotaged."

 "The blame is mine, too," Lucky said calmly. "Iwas on board ship and did not prevent it. Neverthe­less, if we can bring back the saboteur, there will beno question of court-martial."

 The commander said, "The saboteur, of course, is

                                                                               153

 the robot you warned me of. How I could be soblind!"

 "I'm afraid you still don't see entirely. It wasn'tthe robot."

 "Notthe robot?"

 "A robot could not have sabotaged the ship. Itwould have been bringing harm to humans and thatwould have meant breaking the First Law."

 The commander frowned as he considered that."It might not have been aware that it was doingharm."

 "Everyone aboard ship, including the humanoid,understands Agrav. The robot would have known itwas doing harm. In any case I think we have theidentity of the saboteur, or will have in a moment"

 "Oh? Who is he, Councilman Starr?"

 "Well, consider this for a moment. If a man so sabo­tages a ship as to insure that it will either blow up or fall into Jupiter, he would be either a madman or a superhumanly dedicated person to stay on board thatship."

 "Yes, I suppose so.''

 "Since the time we left Io, the air locks have neveropened. If they had there would have been slight dropsin air pressure, and the ship's barometer indicates nosuch drops. You see, then, the saboteur must neverhave gotten on the ship at Io. He's still there, unless he's been taken off."

 "How could he be taken off? No ship could get to Io, except this one."

 Lucky smiled grimly. "NoEarth ship."

 The commander's eyes widened. "Surely no Sirianship, either."

 54                       

 "Are you sure?"

 "Yes, I'm sure." The commander frowned. "And for that matter, wait a moment. Everyone reported on board before we left Io. We wouldn't have left without everyone reported present."

 "In that case everyone is still on board."

 "I would presume so."

 "Well," said Lucky, "Panner has ordered all men to stations under emergency conditions. The where-abouts of every man should be fixed during this dryrun. Call Panner and ask if anyone is missing."

 Commander Donahue turned to the intercom, andsignaled Panner.

 There was some delay, and then Panner's voice,infinitely tired, answered. "I was about to call, Com­mander. The run was successful. We can take off. Ifwe're lucky, things will hold till we're back on JupiterNine."

 The commander said, "Very good. Your work will be properly acknowledged, Panner. Meanwhile, are allmen at stations?"

 Panner's face on the visiplate above the intercomseemed to harden all at once."No! By Space, I meantto tell you! We can't locate Summers."

 "Red Summers," Bigman cried in sudden excite­ment. "That murdering cobber. Lucky . . ."

 "One moment, Bigman," Lucky said. "Dr. Panner,you mean Summers isn't in his quarters?"

 "He isn't anywhere. Except that it's impossible, I'dsay he wasn't on board."

 "Thank you." Lucky reached over to break contact"Well, Commander."

 Bigman said, "Listen, Lucky. You remember once

                                                                               155

 I told you I met him coming out of the engine room?What was he doing down there?"

 "We know now," said Lucky.

 "And we know enough to get him," said thecommander, white-faced. "We're landing on Ioand . . ."

 "Wait," said Lucky, "first things first. There issomething more important even than a traitor."

 "What?"

 "The matter of the robot."

 "That can wait."

 "Perhaps not. Commander, you said that all menreported on board theJovian Moon before we left lo.If so, the report was obviously a false one."

 "Well?"

 "I think we ought to try to find the source of thefalse report. A robot can't sabotage a ship, but if a man has sabotaged the ship without the robot's knowledge,it would be very simple for the robot to help that manremain off the ship if its help is requested."

 "You mean whoever is responsible for the false re­port that Summers was on board ship is the robot?"

 Lucky paused. He tried not to allow himself to growtoo hopeful or feel too triumphant, and yet the argu-men seemed perfect.

 He said, "It seems so."

 15

 Traitor!

 Commander Donahue said, "Major Levinson, then."His eyes darkened. "And yet I findthat impossible tobelieve."

 "Find what impossible to believe?" Lucky asked.

 "That he is a robot. He's the man who took the re­port. He keeps our records. I know him well and Iswear that hecan't be a robot."

 "We'll question him, Commander. And onething—" Lucky's expression was somber. "Don'taccuse him of being a robot; don't ask him if he's oneor even imply that he might be one. Do nothing tomake him feel he's under suspicion."

 The commander looked astonished. "Why not?"

 "The Sirians have a way of protecting their robots. Open suspicion may trigger some explosive devicewithin the major if he is indeed a robot."

 The commander exhaled explosively. "Space!"

 Major Levinson showed the signs of strain that wereuniversal among the men aboard theJovian Moon,but he stood at brisk military attention. "Yes, sir."

 157

 158                     

 The commander said cautiously, "Councilman Starrhas a few questions to ask."

 Major Levinson shifted to face Lucky. He was quitetall, topping even Lucky's inches, with fair hair, blueeyes, and a narrow face.

 Lucky said, "All men were reported on board theJovian Moonat the tune of take-off from Io, and youprepared that report. Isthat right, major?"

 "Yes, sir."

 "Did you see each man individually?"

 "No,sir. I used the intercom. Each man answeredat take-off station or in his cabin."

 "Each man? Did you hear each man's voice? Eachindividual voice?"

 Major Levinson looked astonished. "I suppose so.That's not the sort of thing one remembers, really."

 "Nevertheless it's quite important and I'm askingyou to remember."

 The major frowned and bent his head. "Well, nowwait. Come to think of it, Norrich answered for Sum­mers because Summers was hi the bathroom." Then,with a sudden spark of excitement, he added, "Hold on, they're looking for Summers right now."

 Lucky held up a palm. "Never mind that, Major. Would you get Norrich and send him up?"

 Norrich came in on Major Levinson's arm. Helooked bewildered. He said, "Commander, no oneseems to be able to find Red Summers. What's hap-pened to him?"

 Lucky forestalled the commander's answer. He said,"We're trying to find out. Did you report Summers present when Major Levinson checked those aboardbefore we left Io?"

 159

 The blind engineer reddened. He said tightly, "Yes."

 "The major says you said Summers was in the bath­room. Was he?"

 "Well . . . No, he wasn't, Councilman. He hadgotten off ship for a moment to pick up some item ofequipment he had left behind. He didn't want the com­mander chewing him out—pardon me, sir—for care­lessness, and he asked me to cover for him. He saidhe would be back well before take-off."

 "Was he?"

 "I...I thought...I had the impression hewas. Mutt barked, I think, and I was sure Summerswas coming back, but there isn't anything for me to doat take-off, so I was turning in for a nap and I guess I just didn't give the matter too much thought at themoment. Then there was the mess in the engine roomalmost right away, and after that there was no time to think of anything."

 Panner's voice came over the central intercom with sudden loudness. "Warning to all men. We are takingoff. Everyone to stations."

 TheJovian Moon was in space again, lifting itself against Jupiter's gravity with powerful surges. It wasexpending energy at a rate that would have bankruptedfive ordinary vessels and only the fault tremor in thesound of the hyperatomics remained to show that theship's mechanism depended, in part, on makeshiftdevices.

 Panner gloomily pondered on the poor showing theship would now make energy-wise. He said, "As is, I'll get back with only seventy per cent of originalenergy, when it could have been eighty-five or ninety.

 160                      

 If we land on lo and make another take-off, we'll get back with only fifty. And I don't know if we can stand another take-off."

 But Lucky said, "We must get Summers, and you know why."

 With lo growing large-sized once again in the visi-plate, Lucky said thoughtfully, "It's not entirely certainwecan find him, Bigman."

 Bigman said incredulously, "You don't think theSirians actually picked him up, do you?"

 "No, but Io's a big place. If he wanders off to somerendezvous, we might never locate him. I'm countingon his staying put. He'd have to carry air, food, andwater with him if he moved, so it would be most logicalfor him to stay put. Particularly when he'd have noreason to expect us to come back."

 Bigman said, "We should have known it was that cobber all along, Lucky. He tried to kill you first thing.Whyshould he want to do that, if he weren't playing along with the Sirians?"

 'True enough, Bigman, but remember this: we were looking for a spy. Summers couldn't be the spy. He had noaccess to the leaked information. Once it was clear to me that the spy was a robot, that cleared Summers on another account. The V-frog had detected emotion

 inhim, so he couldn't be a robot and therefore couldn't be the spy. Of course that didn't prevent him from be-ing a traitor and saboteur, and I should not haveallowed the search for a spy to blind me to that possibility."

 He shook his head and added, "This seems to be a case riddled with disappointment. If it had been any-

 161

 one elsebut Norrich who had covered for Summers,we would have had our robot. The trouble is thatNorrich is the only man who could have had convinc­ingly innocent reason to co-operate with Summers. Hewas friendly with Summers; we know that. Then, too, Norrich could innocently be ignorant that Summers never returned before take-off. After all, he's blind."

 Bigman said, "Besides which, he showed emotion,too, so he can't be the robot."

 Lucky nodded. "True enough." Yet he frowned andgrew silent.

 Down, down they came to Io's surface, landing al­most in the marks of their previous take-off. The dotsand smeared shadows in the valley resolved themselvesinto the equipment they had set up as they approached.

 Lucky was surveying the surface intently through the visiplate. "Were any air tights left behind on Io?"

 "No," said the commander.

 "Then we may have our man. One air tight, as youmay notice, is fully expanded behind that rock forma­tion. Do you have the list of material unaccounted for0n board?"

 The commander delivered a sheet of paper withoutcomment, and Lucky studied it. He said, "Bigman andI will go out after him. I doubt that we'll need help."

 The tiny sun was high in the sky, and Bigman and Lucky walked on their own shadows. Jupiter was athinnish crescent.

 Lucky spoke on Bigman's wave length. "He must have seen the ship unless he's sleeping."

 "Or unless he's gone," said Bigman.

 "Idoubt that he's gone."

 162                      

 And almost at once Bigman cried, "Sands of Mars,Lucky, look up there!"

 A figure appeared at the top of the line of rock. Itstood out blackly against the thinning yellow line ofJupiter.

 "Don't move," came a low, tired voice on Lucky'sown wave length. "I'm holding a blaster."

 "Summers," said Lucky, "come down and surren­der."

 A note of bitter mockery entered the other's strained voice. "I guessed the right wave length, didn't I, Coun­cilman? Though it was an easy guess from the size ofyour friend . . . Get back to your ship or I'll kill youboth."

 Lucky said, "Don't bluff pointlessly. At this distanceyou couldn't hit us in a dozen tries."

 Bigman added with tenor fury, "And I'm armed, too, and I can hit you even atthis distance. Justremember that and don't even move a finger near theactivating button."

 Lucky said, "Throw down your blaster and sur­render."

 "Never!" said Summers.

 "Why not? To whom are you being loyal?" Luckydemanded. "The Sirians? Did they promise to pick youup? If so, they lied to you and betrayed you. They're not worth loyalty. Tell me where the Sirians' base in the Jupiter system is located."

 "You know so much! Figure it out for yourself."

 "What subwave combination do you use to contactthem?"

 "Figure that out, too . , . Don't move any closer."

                                                                              163

 Lucky said, "Help us out now, Summers, and I'll domy best to get you mild treatment on Earth."

 Summers laughed weakly. "The word of a council­man?"

 "Yes."

 "I wouldn't take it. Get back to your ship."

 "Why have you turned against your own world,Summers? What have the Sirians offered you?Money?"

 "Money!" The other's voice was suddenly furious. "Do you want to know what they offered me? I'll tellyou. A chance at a decent life." They could hear thetiny gritting sound Summers made as his teeth groundtogether. "What did I have on Earth? Misery all my life. A crowded planet with no decent chance at mak­ing a name and a position for myself. Everywhere I went I was surrounded by millions of people clawingat each other for existence, and when I tried to clawalso, I was put in jail. I made up my mind that if everI could do anything to get back at Earth, I would."

 "What do you expect to get from Sirius in the wayof a decent life?"

 "They invited me to emigrate to the Sirian planets,if you must know." He paused, and his breathing madesmall whistling noises. "New worlds out there. Cleanworlds. There's room for men there; they need menand talent. I'd have a chance there."

 "You'll never get there. When are they coming foryou?"

 Summers was silent

 Lucky said, "Face it, man. They're not coming foryou. They have no decent life for you; no life at all for

 164                      

 you. Only death for you. You expected them before this, didn't you?"

 "I didn't."

 "Don't lie. It won't improve the situation for you.We've checked the supplies missing from theJovianMoon.We know exactly how much oxygen you smug­gled off the ship. Oxygen cylinders are clumsy thingsto carry even under Io's gravity when you have to sneak them off without being caught and in a hurry.Your air supply is almost gone now, isn't it?"

 "I have plenty of air," said Summers.

 Lucky said, "I say it's almost gone. Don't you seethe Sirians aren't coming for you? They can't come foryou without Agrav and they haven't got Agrav. Great Galaxy, man, have you let yourself get so hungry forthe Sirian worlds that you'll let them kill you in as open and crude a double-cross as I've ever seen? Now, tellme, what have you done for them?"

 Summers said, "I did what they asked me to do andthat wasn't much. And if I have any regrets," heshouted in sudden, breathless bravado, "if s only that Ididn't get theJovian Moon. How did you get away,anyway? I fixed it. Ifixed the rotten, slimy . . ." heended, choking.

 Lucky motioned to Bigman and broke into the soar­ing lope characteristic of running on low-gravityworlds. Bigman followed, veering off so as not to offera single target.

 Summers' blaster came up and made a thin poppingsound, all that was possible in Io's thin wisps ofatmosphere. Sand kicked up and around, and a craterformed yards from Lucky's fleeting figure.

 "You won't catch me," Summers yelled with a kind

 165

 of weak violence. "I'm not coming back to Earth.They'll come for me. The Sirians will come for me."

 "Up, Bigman," said Lucky. He had reached the rockformation. Jumping upward, he caught a projectionand hurled himself further upward. At sixth-normalgravity, a man, even in a space suit, could outdo amountain goat in climbing.

 Summers screamed thinly. His hands moved up to his helmet and he leaped backward and disappeared.

 Lucky and Bigman reached the top. The rockformation was nearly sheer on the other side, withsharp outcroppings breaking the clifflike face. Sum­mers was a spread-eagled figure, dropping slowlydownward, striking against the face of the rock, andrebounding.

 Bigman said, "Let's getlam, Lucky," and jumped far outward, wide of the cliff. Lucky followed.

 It would have been a killing leap on Earth, even onMars. On Io it was little more than a tooth-jarringdrop.

 They hit with bent knees and let themselves roll totake up some of the force of impact. Lucky was on hisfeet first and made for Summers, who lay prone andunmoving.

 Bigman came up panting. "Hey, that wasn't theeasiest jump I— What's the matter with the cobber?"

 Lucky said grimly. "He's dead. I knew his oxygenwas low from the way he sounded. He was almostunconscious. It's why I rushed him."

 "You could go a long time being unconscious,"said Bigman.

 Lucky shook his head. "He made sure. He reallydidn't want to be taken. Just before he jumped, he

 166                       

 opened his helmet toid's poison air and he hit thecliff."

 He stepped aside and Bigman caught a glimpse ofthe smashed face.

 Lucky said, "Poor fool!"

 "Poortraitor!" Bigman raged. "He might have hadthe answer and he wouldn't tell us. Now he can't tellus."

 Lucky said, "He doesn't have to, Bigman. I think Iknow the answer now."

 16

 Robotl

 ''You do?" The little Martian's voice rose to a squeak."What is it, Lucky?"

 But Lucky said, "Not now." He gazed down atSummers, whose dead eyes stared sightlessly towardthe alien heavens. He said, "Summers has one distinc­tion. He is the first man ever to die on Io."

 He looked up. The sun was edging behind Jupiter.The planet was becoming only a faint silvery circle oftwilit atmosphere.

 Lucky said, "It will be dark. Let's go back to theship."

 Bigman paced the floor of their cabin. It took onlythree steps one way, three steps the other, but hepaced. He said, "But if youknow, Lucky, why don'tyou . . ."

 Lucky said, "I can't take ordinary action and riskexplosion. Let me do it in my own time and my own way, Bigman."

 There was a firmness in Ms tone that quite subduedBigman. He changed the subject and said, "Well, then, why waste any more time on Io because of that cobber

 167

 168                      

 out there? He's dead. There's nothing more to doabout him."

 "One thing," said Lucky. The door signal flashedand he added, "Open it, Bigman. It should be Norrich."

 It was. The blind engineer stepped in, his dog,Mutt, going before.

 Norrich's blue, unseeing eyes blinked rapidly. Hesaid, "I've heard about Summers, Councilman. It's aterrible thing to think he tried to...to...Terri­ble that he was a traitor. Yet somehow I'm sorry forhim."

 Lucky nodded. "I knew you would be. It's why I asked you to come here. It's dark out on lo now. Thesun's in eclipse. When the eclipse is over, will youcome out with me to bury Summers?"

 "Gladly. We should do that much for any man, shouldn't we?" Norrich's hand dropped as if for con­solation on Mutt's muzzle, and the dog came close andmoved softly against his master as though feeling somedim need to offer sympathy.

 Lucky said, "I thought you would want to comealong. After all, you were his friend. You might wantto pay your last respects."

 "Thank you. I would like to." Norrich's blind eyeswere moist.

 Lucky said to Commander Donahue just before he placed the helmet over his head, "It will be our last tripout. When we return, we will take off for Jupiter Nine."

 "Good," the commander said, and there seemedsome unspoken understanding as their eyes met.

 Lucky put on his helmet and in another corner ofthe pilot room, Norrich's sensitive fingers moved deli­cately over Mutt's flexible space suit, making sure all

                                                                               169

 fastenings were secure. Inside the glass-fronted, odd-shaped helmet that fitted over Mutt's head, Mutt'sjaws moved in a faintly heard bark. It was obvious thedog knew he was headed for a trip into low gravity andthat he enjoyed the prospect

 The first grave on Io was done. It had been dug outof hard, rocky soil by the use of force diggers. It wasfilled in with a mound of gravel and topped by an ovalboulder as a marker.

 The three men stood round it while Mutt wanderedoff in the distance, trying vainly, as always, to examinehis surroundings, though metal and glass blocked theuse of his sense of smell.

 Bigman, who knew what Lucky expected him to dobut didn't know why, waited tensely.

 Norrich stood with his head bowed and said softly,"This was a man who wanted something very much,did wrong for that reason, and has paid for it."

 "He did what the Sirians asked him to do," Lucky added. "That was his crime. He committed sabotageand . . ."

 Norrich stiffened as the pause in Lucky's remarkslengthened. He said, "Andwhat?"

 "And he gotyou on board ship. He refused to jointhe crew without you. You yourself told me that it wasonly through him that you were assigned to theJovianMoon."

 Lucky's voice grew stern. "You are a robot spyplaced here by the Sirians. Your blindness makes youseem innocent to the others on the project, but youdon't need a sense of sight. You killed the V-frogand covered for Summers to get him off the ship. Your

 170                      

 own death meant nothing to you hi the face of orders, as Third Law states. And, finally, you fooled me bythe display of emotion I caught through the V-frog, a synthetic emotion built into you by the Sirians."

 This was the cue for which Bigman had been wait­ing. Lifting the butt of his blaster high, he hurledhimself at Norrich, whose incoherent protestations did not coalesce into words.

 "I knew it was you," Bigman shrieked, "and I'msmashing you."

 "It's not true," Norrich wailed, finding his voice. Hethrew up his hands and stumbled backward.

 And suddenly Mutt was a streak in the pale, white light. He hurled himself furiously across the quarter mile that separated him from the men, aiming withdesperate passion at Bigman.

 Bigman paid no attention. One hand caught at Nor-rich's shoulder. The other swung the blaster upward.

 Then Mutt collapsed!

 While he was still ten feet from the struggling pair, his legs stiffened uselessly and he tumbled and rolled past them, coming to a frozen halt at last. Through theglass of his helmet his jaws could be seen hangingopen, as though in mid-bark.

 Bigman held his threatening position over Norrichas though he, too, were frozen.

 Lucky approached the animal with quick steps. He used his force shovel as a kind of unwieldy knife and slit Mutt's space suit lengthwise from neck to tail.

 Then, tensely, he slit through the skin at the back ofthe neck and probed deftly with his mail-shod fingers.They closed on a small sphere that was not bone. Helifted the sphere and met resistance. Holding his breath,

 171

 he snapped the wires that held it in place and stood up,almost weak with relief. The base of the brain had beenthe logical place for a mechanism to be activated bythe brain, and he had found it. Mutt could endangerno one now.

 Norrich cried out, as though through instinctiveknowledge of his loss.

 "My dog! What are you doing to my dog?"

 Lucky said softly, "If s no dog, Norrich. Never was.It was a robot. Come, Bigman, lead him back to the ship. I'll carry Mutt."

 Lucky and Bigman were in Panner's room. TheJovian Moonwas in flight again, and Io was fallingrapidly away, already only a bright coin in the sky.

 "What gave it away?" said Panner.

 Lucky said somberly, "A number of things which Inever saw. Every clue pointed firmly to Mutt, but I wasso intent on finding a humanoid robot, so inwardlyconvinced that a robot had to look human, that Ilooked past the truth though it stared me in the face."

 "Then whendid you see?"

 "When Summers killed himself by jumping off therock. I stared at him, lying there, and thought of Big­man falling through the ammonia snow and nearlydying. I thought: There's no Mutt that can save thisone. . . . And that did it."

 "How? I don't understand."

 "Howdid Mutt save Bigman? When the dog camerunning up past us, Bigman was somewhere under theice, nowhere to be seen. Yet Mutt plunged in, madefor Bigman without hesitation, and dragged him out.We accepted that without thought because we some­how expect dogs to find what can't be seen through

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 their sense of smell. But Mutt's head was enclosed. Hecould neither see nor smell Bigman, yet had no troublelocating him. We ought to have seen that unusual senseperception was involved. We'll find out exactly whichwhen our roboticists work over the carcass."

 "Now that you explain," said Panner, "it looks plain enough. The dog had to give itself away because FirstLaw compelled it not to allow a human being to cometo harm."

 "That's right," said Lucky. "Once suspicions ofMutt finally penetrated, a few other things started fall­ing into place. Summers had maneuvered Norrich onboard, yes, but in doing so, he also got Mutt on board.Moreover, Summers was the one who got Mutt forNorrich in the first place. The chances are that thereis a spy ring on Earth whose only task is to distributethese robot dogs to people working in or near critical research centers.

 "Dogs are perfect spies. If you find a dog nosingthrough your papers or walking through a super-secretsection of a laboratory, are you concerned? Chancesare you pet the dog and feed him a dog biscuit. Ichecked through Mutt as best I could and I think hehas a built-in subetheric transmitter which keeps him in contact with his Sirian masters. They can see whathe sees, hear what he hears. For instance, they sawthe V-frog through Mutt's eyes, recognized its danger, and directed him to kill it. He could be made to handlean energy projector with which to fuse the lock of adoor. Even if he was caught in the act, there was agood chance we would put it all down to the accidentalhappenings of a dog playing with a weapon he hadfound.

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 "But once all this had occurred to me, I was only at the beginning of the practical problem. I had to try totake the dog intact. I was sure that any obvious suspi­cion of Mutt would trigger an explosion inside him.So first I brought Norrich and Mutt to a safe distancefrom the ship by suggesting we dig Summers' grave.In that way if Mutt did explode, the ship, at least, andits men would escape. Naturally I left a note with Com­mander Donahue, to be opened in case I did not return,so that Earth would at least investigate dogs in re­search centers.

 "I then accused Norrich . . ."

 Bigman broke in, "Sands of Mars, Lucky, for awhile I thought you really meant it when you said Norrich had killed the V-frog and fooled us withbuilt-in emotion."

 Lucky shook his head. "No, Bigman. If he couldfool us with built-in emotion, why bother to kill theV-frog? No, I was making sure that if Sirians were listening through Mutt's senses, they would be con­vinced I was on the wrong track. In addition, I was setting up a situation for Mutt's benefit.

 "You see, Bigman, under instructions, attacked Norrich. As a Seeing Eye dog, Mutt was built withstrong orders to defend his master against attack, andobedience to orders are Second Law. Usually there'sno problem here. Few people attack a blind man andthose who do will usually stop if the dog simply growlsand bares its fangs.

 "But Bigman persisted in his attack, and Mutt, forthe first time since being built, had to carry throughall the way. But how could he? He couldn't hurt Big-man. First Law. Yet he couldn't allow Norrich to be

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 hurt either. It was a complete dilemma and Mutt wentout of commission. Once that happened, I gambledthat any bomb he contained could no longer be trig­ gered. So I removed it and after that we were safe."

 Panner took a deep breath. "Very neat."

 Lucky snorted. "Neat? I could have done this the first day I landed on Jupiter Nine, if I had my witsabout me. I almost had it, at that. The thought was atthe edge of my mind constantly and I never caught it."

 Bigman said, "What was it, Lucky? I still don'tknow."

 "It was simple enough. The V-frog detected animalemotion as well as human emotion. We had an exam­ ple of that when we first landed on Jupiter Nine. Wedetected hunger in the mind of a cat. Then, later, we met Norrich and he urged you to aim a blow at him inorder to show off Mutt's protectiveness. You did so. Idetected Norrich's emotions and yours, Bigman, through the V-frog, but although Mutt showed every outward sign of anger, I detected no trace of such anemotion. There was the absolute proof as early as that,that Mutt had no emotions and was therefore no dogbut a robot. Yet I was so convinced that I was lookingfor some human that my mind refused to see thatpoint. . . . Well, let's go to dinner and visit Norrichon the way. I want to promise him that we'll get himanother dog, a real one."

 They arose, and Bigman said, "Anyway, Lucky,maybe it took some time, but we've stopped theSirians."

 Lucky said quietly, "I don't know that we've stoppedthem, but certainly we've slowed them down."

 ABOUT THE AUTHOR

 Isaac Asimov was born in the Soviet Union to hisgreat surprise. He moved quickly to correct the situation.When his parents emigrated to the United States, Isaac(three years old at the time) stowed away in theirbaggage.' He has been an American citizen since theage of eight.

 Brought up in Brooklyn, and educated in its publicschools, he eventually found his way to Columbia University and, over the protests of the school admin­istration, managed to annex a series of degrees inchemistry, up to and including a Ph.D. He then infiltratedBoston University and climbed the academic ladder,ignoring all cries of outrage, until he found himselfProfessor of Biochemistry.

 Meanwhile, at the age of nine, he found the love ofhis life (in the inanimate sense) when he discovered hisfirst science-fiction magazine. By the time he was eleven,be began to write stories, and at eighteen, he actuallyworked up the nerve to submit one. It was rejected. Afterfour long months of tribulation and suffering, he sold his first story and, thereafter, he never looked back.

 In 1941, when he was twenty-one years old, hewrote the classic short story' "Nightfall" and his future was assured. Shortly before that he had begun writinghis robot stories, and shortly after that he had begun his Foundation series.

 What was left except quantity? At the present time, he has published over 260 books, distributed throughevery major division of the Dewey system of library classification, and shows no signs of slowing up. Heremains as youthful, as lively, and as lovable as ever, andgrows more handsome with each year. You can be surethat this is so since he has written this little essay himself and his devotion to absolute objectivity is notorious.

 He is married to Janet Jeppson, psychiatrist and writer,has two children by a previous marriage, and lives inNew York City.