John Hall wiped away blood that trickled from his mouth. Painstakingly he disengaged himself from the hopeless wreckage of the control room. He staggered free, his lungs pumping with terrific effort to draw enough oxygen from the thin, bitterly cold air of Ganymede—that had rushed in when his helmet had been shocked open.

Feeling unusually light he walked over to an enormous tear in the side of his space-cruiser. A bleak scene met his eyes. Short, grotesquely hewn hills and crags. Rocky pitted plains. And a bitter, wild wind blew constantly, streaming his long hair into disarray.

He cursed through tight lips. Fate! He had been on his way to Vesta, largest city of Jupiter, when his fuel had given out. He had forgotten to check it, and here he was.

Despondently he kicked a small rock in front of him. It rose unhindered by the feeble gravitation fully thirty feet in the air.

Suddenly there were a dozen scuffing sounds, and a dozen stones winged themselves painstakingly through the air and began to descend in slow motion.

Surprise struck, he gazed furtively about him. Momentarily his heart seemed caught in some terrible vise.

There was a sudden movement behind a close ridge. Momentarily John Hall was rendered paralyzed. Then he backed slowly toward the ship and safety behind a Johnson heat ray. The vague form abruptly materialized, etched in black against the twilight horizon of Ganymede. The effect was startling. The creature stood upright, on two legs, with two gnarled, lengthy arms dangling from its bony shoulders. Human? The question registered itself on his brain, and the thing in front of him gave unwitting reply, as it moved to a clearer position. No, not human. Maybe not even animal. Two great eyes bulged curiously from a drawn, shrunken, monkey-like face. The body was as warped and distorted as the bole of an old oak tree. With pipe-stem arms and legs, bulging at the joints. Its most natural position seemed to be a crouch, with the arms dragging on the ground. Somehow this travesty of human form struck him as being humorous. He chuckled throatily, and then stopped with a start as the same chuckle crudely vibrated back, echo-like. But it was no echo! No, that wasn't possible. John raised his hand to scratch his head through force of habit; forgetful that this was impossible through the thick glassite helmet he wore. The tall, gangling creature in front of him watched closely for a moment, then stretched one preposterously long limb up and scratched briskly on his leathery skull in imitation of John Hall.

The answer struck him instantly. Why hadn't he thought of it. This animal, this thing, whatever it was, was a natural mimic. Such a thing was not unknown on earth. Monkeys often imitated the gestures of humans. Parrots prattled back powerful expletives and phrases. He rather welcomed his new find now. It would be pretty dismal all alone on desolate Ganymede with no one to talk to but himself, and this strange animal would undoubtedly help to lighten the long, dreary hours, perhaps days, that stretched ahead of him until rescue came. Certainly there was nothing to fear from this creature; not at least by himself, born to resist the pull of a gravity force many times more powerful then that of Ganymede's.

He walked slowly toward the creature viewing its reactions carefully. It held its ground. Evidently fear was not an element in its makeup. Why should it be? Doubtlessly these things were the only animate life on the globe. Masters of all they surveyed. No other beings to contest their supremecy. No need then for fear or even for savageness. They were, undoubtedly, happy-go-lucky beasts who scavenged the bleak, rocky surface of the moon for hardy mosses or whatever they lived on. He heard a scuffing noise to his left. Another creature, similar almost in every detail to the first had popped into view. That seemed to be a signal for a dozen others to haphazardly appear from the most unexpected places and niches. One rose up within a few feet of Hall and blinked its great eyes at him in greeting.

"What the—", Hall spluttered to himself, "seems to be a family reunion of some sort." Suddenly, prompted by some impish quirk he shouted to his bizarre audience, "Hello there." A moment of silence and then a chorus of rasping sounds sent back "Ah-low-da." Probably the closest that their crude vocal apparatus could interpret his alien accents. Continuing his mock procedure, John stretched his hands aloft, and then in stiff, prim fashion bowed low. With solemn dignity the assembly emulated his action. John leaped twenty feet into the air with glee, and as he floated slowly to the ground he watched the pitiful attempts below to equal his feat.

For a moment everything was still and John good-naturedly surveyed the grotesque caricatures of human beings that surrounded him. "Well," John finally commented candidly, "at least we are in agreement over what line of action to follow, which is more than I could say for a lot of human friends of mine." A blurred attempt at imitation followed.

Then abruptly it was dark. Just like that. Perhaps you have seen darkness fall in the tropics? Just ten or fifteen minutes of twilight and then it's dark. The thin atmosphere of Ganymede did not maintain twilight very long. John cursed a little as he backed his erratic way back to the ship, revealed only by the gleam of the stars on its rounded hull. He groped about for the tear in the surface of the glimmering shell, found it and tumbled hastily in to escape the terrible cold that was forming in the absence of the sun's heat. The pilot room was rapidly assuming the aspect of an underground cavern with long, gleaming icicles hanging from the top. John grumbled a bit, and then opened the door to the small supply room. Closed it quickly behind him and sat down on a box of canned beans. Funny, he reflected, that they had never been able to produce synthetic foods in feasible form. Perhaps habit was harder to change than the scientists had thought. People still liked their meals—solid. He reached out and switched on the feeble storeroom light which operated from an independent source. Its yellow glow brought back a comforting nostalgia. He dined frugally on a can of beans and some biscuits; turned the heating units of his suit up to 70 degrees, and dozed into fitful slumber.

Some indeterminate period later he awoke. His mind still a little numbed by sleep he slipped the catch on his helmet and threw it back in order to take advantage of the bracing effect the sharp, thin air of Ganymede had displayed on the previous evening. He was totally unprepared for the furnace-like blast of heat that swept across his exposed features. He stood for a moment, stupefied, while the oven-heat dried the juices of his face and started to take on a blistering effect. Comprehension dawned magically and he snapped back the helmet and breathed with distinct relief the air supplied by his space suit which was scientifically kept at a pleasant temperature. The explanation was simplicity itself. The air cover of Ganymede was so thin, and its cloudless skies so clear, that the sun, though distant, beat down like old fury itself. He opened the door that led from the supply room into the pilot room. The long, pointed icicles which had formed the previous night were gone. The only clue to show that they had once existed was a rapidly rising cloud of steam from the steel floor. His glassite helmet misted swiftly as he walked through the room, then cleared slowly as he stepped out into the full glare of the sun. He could not help but admire the potency of this yellow star, even from a distance at which it appeared hardly larger than a standard sized base ball.

He cupped one heavily encased hand over the top of his helmet to protect his eyes from the sun, and searched the skies thoroughly for any sign of a rescue ship. Sighting nothing he dropped his hand despondently to his side and stumbled thoughtfully along the rough terrain. His mind worked desperately, attempting to devise some feasible means of signaling the rescue parties which must, at this very moment, be combing the space lanes—searching for him. Some huge flare might be useful, but a simple glance about him revealed that the largest form of plant life, which might serve as fuel, were small grey mosses that grew on the underside of occasional outcropping rock formations. They were useless for anything but a tiny smudge fire. His mind turned back to his ship. Possibly there was something highly combustible aboard that might be used for a flare. His mind flitted thoughtfully over every item in the ship's supplies and retired with the conclusion that the anti-fire campaigns which had been conducted for so long on the inhabited planets were going too far! His only hope lay in the possibility that one of the rescue ships might briefly scan the surface of Ganymede with one of their telescopic vision plates and notice the gleaming wreck of his auxiliary space ship. That gave him an idea. Something he had once used in an old book. About a castaway on a desert island arranging rocks to spell out giant words in the hope that some passing airplane might see the message and land to investigate. Slim chance, but still nothing could be overlooked if he hoped for eventual rescue.

Swiftly he set about gathering rocks. He planned to form the simple four letter word HELP, with an exclamation point added for emphasis. So engrossed was he in his work that he scarcely noted the unusual volume of noise about him, or if he did notice it attributed it to the small slides caused by his unearthing rocks from their natural formation. Hours passed while he painstakingly formed the shape of an enormous letter "H," a letter fully a tenth of a mile long. Exhausted by the unaccustomed manual labor he straightened up a moment and cast an approving eye across the extent of his handiwork. A gasp rose involuntarily from his throat as a strange sight crossed his line of vision. The land about him fairly swarmed with the peculiar, bony creatures he had encountered the evening before, and as far as his eyes could see there stretched an uninterrupted series of H's, all exactly similar in shape, size and peculiarities of the original! And at the edge of each of the letters sat a puffing group of emaciated, leathery skinned Ganymedians! Their great, watery eyes blinking patiently and soulfully in his direction!

He didn't know whether to laugh or to cry. It was impossible to proceed. In order to lay out another letter he would have to accomplish the tremendous task of removing all the other H's as well. He shuddered as he realized that he would have to repeat the process again and again until finally the one word help, with a string of exclamation points miles in length remained. Suddenly a thought struck him. Wasn't this seemingly endless row of huge H's sufficient to attract the attention of any searching party that happened to see it without going to the trouble, double trouble at that, of adding the rest of the letters that spelled out the word HELP? It seemed logical enough to him. With a distinct air of relief he turned away, his arduous task of the past few hours completed, thanks to these freakish creatures that inhabited this moon.

Again the beginning of the short twilight was progressing and the sun was settling rapidly in the sky—its glare and heat diminishing with each passing moment. The massive bulk of Jupiter above could be seen only as a long, thin, crescent that stretched one quarter of the way across the visible sky. He experimentally lifted his helmet an inch or two. A sharp gust of air scurried hurriedly around the contours of his face and slightly ruffled his hair. He threw the helmet all the way back and with exultation breathed in tremendous gulps of crisp, fresh air. For the first time that day his powerful frame rose to its full six feet of height and he stood statuesque, his shadow cast before him, a symbol of man against the cosmos.

Still, somehow his mind could not shift from the ever-present danger. Possible exhaustion of his food supply; the energy heating units of his space suit—of water. Once again his thoughts turned to the humor provided by the strange inhabitants of Ganymede. He called out sharply to one of them: "How are you old chap?"

"How're you all chap," the grating reply floated back, thinned by the sparse atmosphere. Some guttural effect in the creature's voice seemed to place the emphasis on the word "you." And it sounded uncannily like a return question, infinitely more so than the echo-like effect it should have had! And also the speech had improved! Very definitely improved! Where before they had relayed back his sentences in an indistinguishable blur of sound, now some of the words stood out, sharp, clear!

"This chap doesn't need enunciation lessons," John muttered softly to himself. And as if to prove it the lips of the creature moved erratically, as if talking to itself in the identical manner that John had just done.

"Nice weather we're having," John phrased ironically as small flakes of ice formed on the end of his nose.

"Like hell it is!" came back the surprise retort.

John stood there aghast. The creature had emitted the very same reply that he had been thinking, but had not voiced!

The Ganymedian in front of him took on a more surprising aspect with each passing moment. For some reason nature had bestowed upon this travesty of human form a telepathic mental pick-up. Similar, in results, to the ones in use on earth, except that this was not a mechanical device. It was, undoubtedly, a far more efficient receiver of flesh and blood, or whatever substance this thing was composed of, capable of picking up thought waves as simply as a radio receiver picks up radio waves.

"It can do anything but understand," John found himself saying. He could only wonder why some scientist had not discovered these creatures before and dissected them to find out just how their peculiar brains operated.

And then, for the first time in many hours, his mind turned back to his fiancee, Joan Crandell. He cursed the stolid fates that had stranded him here on this god-forsaken satellite with a bunch of damn-fool mimics. In his mind he visualized Joan as he had last seen her. The golden, glory-sheen of her hair flowing softly down to her shoulders; her straight little nose and small, firm chin; her piquant expression and oh, so desirable lips. And last, but certainly not least her short, trim figure. Perhaps she wasn't the Venus ideal, but to his mind at least, she was infinitely more lovable—an ancient phrase, "and what's more she's got arms," seemed to go well with that thought. For a little more he accorded himself the luxury of seeing her in his mind's eye, and then slowly, sadly, shook his head, and looked up. His eyes popped in disbelief of what he saw! His hands trembled with fearful delight, wonder and amazement. It couldn't be! It wasn't possible! But there she stood—Joan Crandell! To the tiniest detail as he had seen her last! Here on this crazy moon! In an agony of bewilderment he cried out, "Joan! Joan!" He could say no more. The paralysis of surprise left his limbs and he dashed wildly forward. "Joan!" and his arms reached out to grasp her, and twined about a hard, bony, misshapen, distorted, leathery form! He recoiled in abject horror. These strange creatures—an instant before new toys to amuse and astound him were transformed into terror-ridden monsters. No longer a joke—but a tragedy! Joan, or rather the illusion of Joan was there no longer. In her place stood a stupid, blinking, thing that threatened his very sanity—his existence. Something snapped in his mind!

He ran. Miles he ran. His powerful, earthly muscles lending magic powers to his feet. Across broken, rock-hard plains—stumbling, falling, slipping, across stretches of mountain region and through dim valleys. And night descended upon him. Unfailing, relentless, it settled leaving everything pitch dark. And they followed him. Miles behind, but never giving up, never faltering. A mad man they followed who did not run, but leaped, fifty feet into the air, and screaming at his slow rate of descent barely touched the ground before he was off on another leap, even greater than the preceding one. A dozen times he was speared upon dangerous rocks—the tough substance of his suit the only thing between him and death. And as tiny leaks formed in his suit, the insidious cold crept in slowly, surely, numbing his body until each leap was a little shorter, a little less powerful than the other. Until lost in a maze of bleak mountains he collapsed.

Dawn bolted deer-like over the black hills of Ganymede, and as if it had never interrupted its work, the distant sun beat down upon the frozen landscape with renewed vigor. A lone earth figure rolled over and groaned. Shakily it got to its feet and took a few trembling steps. John Hall, exhausted physically and mentally was all right again. The madness of the preceding night had left him, almost as suddenly as it had come upon him. It was almost as if kind nature had blotted out the portion of his brain which preserved memory, and left his mind, dulled, numb. In a daze, his once proud figure tripped along the devious mountain passes. Too tired to leap—barely capable of moving, John Hall threaded his tortuous way through regions only half recalled. No thoughts, simply a guiding instinct that urged him, warned him, that he must go this way to return to the space ship, and food—maybe rescue.

And a hundred yards behind him, unnoticed, trailed multiple, black, ungainly creatures, who stumbled when he stumbled, fell when he fell.

It was nearing twilight again when John Hall panted back into the region of his space ship. Barely cognizant of what he was doing, he smashed a can of beans against the steel hull of the ship and devoured them without ceremony, animal-like. Then he sat wearily down upon a ruined metal bench and tried to relax. Weakly, but nevertheless desperately, he fought with himself. Trying to clear the cobwebs that cluttered up his brain and reason rationally again. Thoughts, like flitting ghosts, aroused tantilizingly, only to whisk down some hidden channel of his mind before he could fully grasp and comprehend them. One of the grotesque things, creatures, objects, whatever they were, drew close to him, its bulging eyes peering not inquisitively, but fearfully into his. He knew! The eluding coherency of thought came. The answer to the enigma lay in his own mind! His powerful earth mind. Scientists had always been aware that the mind radiates energy thoughts away from it. That one mind is capable of hypnotizing another, even across great distances. These inhabitants of Ganymede, with their acute mental receptivity, were slaves to his more powerful will—his every thought. And against their own desires they followed and imitated him. And through some unknown chemical reaction even took the form, momentarily, of some wished-for object. It was clear. But now again it wasn't. His mind was failing. Falling back into the abyss of blackness and incoherency! He stared a moment at one of the peculiar faces before him and as he stared it changed, grew smooth, black, ebony black—and God—blank! Blank like his mind—part of his mind, for through the rest of it swirled a fantasmagoria of images, and disconnected phrases. He was alone, or almost so. Those things were still here. It was getting darker ... colder ... so cold ... was this all a dream? Then he stopped! For over the blank face of the thing in front of him flickered images, mirroring his thoughts, like some disconnected motion picture!

With incredible strength he tore away the protecting mass of his space suit. The cold wind hit him, knifed him through and through. And he stepped forward. Walking, walking, and suddenly his great hands rose aloft in an agony of sorrow. His mighty voice bellowed above the elements of loneliness, of despair. And always, those grotesque, storm-swept, misshapen creatures fastened their wet, glistening eyes upon him and in the depths of them displayed rage as he displayed it; despair as he displayed it. And when he pounded his clenched fists in powerful blows upon his resounding chest, they pounded their gnarled limbs upon their shrunken chests in powerful mimicry.

When the crew of the rescue ship "Space-Spear" landed, they turned back in horror at a planet of mad-things that shrieked, wept, raged and despaired in a manner that was more than imitation—that was real! And they could not help but shudder inwardly at the terrible fate that had befallen John Hall, and his horrible, unknowing revenge!