It crept along the corridor of the space freighter, fighting the terrible urge of its elements to take the shape of its surroundings. A gray blob of disintegrating stuff, it crept, it cascaded, it rolled, flowed, dissolved, every movement an agony of struggle against the abnormal need to become a stable shape.

Any shape! The hard, chilled-blue metal wall of the Earth-bound freighter, the thick, rubbery floor. The floor was easy to fight. It wasn't like the metal that pulled and pulled. It would be easy to become metal for all eternity.

But something prevented it. An implanted purpose. A purpose that drummed from electron to electron, vibrated from atom to atom with an unvarying intensity that was like a special pain: Find the greatest mathematical mind in the Solar System, and bring it to the vault of the Martian ultimate metal. The Great One must be freed! The prime number time lock must be opened!

That was the purpose that hummed with unrelenting agony through its elements. That was the thought that had been seared into its fundamental consciousness by the great and evil minds that had created it.

There was movement at the far end of the corridor. A door opened. Footsteps sounded. A man whistling to himself. With a metallic hiss, almost a sigh, the creature dissolved, looking momentarily like diluted mercury. Then it turned brown like the floor. It became the floor, a slightly thicker stretch of dark-brown rubber spread out for yards.

It was ecstasy just to lie there, to be flat and to have shape, and to be so nearly dead that there was no pain. Death was so sweet, so utterly desirable. And life such an unbearable torment of agony, such a throbbing, piercing nightmare of anguished convulsion. If only the life that was approaching would pass swiftly. If the life stopped, it would pull it into shape. Life could do that. Life was stronger than metal, stronger than anything. The approaching life meant torture, struggle, pain.

The creature tensed its now flat, grotesque body--the body that could develop muscles of steel--and waited in terror for the death struggle.

Spacecraftsman Parelli whistled happily as he strode along the gleaming corridor that led from the engine room. He had just received a wireless from the hospital. His wife was doing well, and it was a boy. Eight pounds, the radiogram had said. He suppressed a desire to whoop and dance. A boy. Life sure was good.

Pain came to the thing on the floor. Primeval pain that sucked through its elements like acid burning, burning. The brown floor shuddered in every atom as Parelli strode over it. The aching urge to pull toward him, to take his shape. The thing fought its horrible desire, fought with anguish and shivering dread, more consciously now that it could think with Parelli's brain. A ripple of floor rolled after the man.

Fighting didn't help. The ripple grew into a blob that momentarily seemed to become a human head. Gray, hellish nightmare of demoniac shape. The creature hissed metallically in terror, then collapsed palpitating, slobbering with fear and pain and hate as Parelli strode on rapidly--too rapidly for its creeping pace.

The thin, horrible sound died; the thing dissolved into brown floor, and lay quiescent yet quivering in every atom from its unquenchable, uncontrollable urge to live--live in spite of pain, in spite of abysmal terror and primordial longing for stable shape. To live and fulfill the purpose of its lusting and malignant creators.

Thirty feet up the corridor, Parelli stopped. He jerked his mind from its thoughts of child and wife. He spun and stared uncertainly along the passageway from the engine room.

"Now, what the devil was that?" he pondered aloud.

A sound--a queer, faint yet unmistakably horrid sound was echoing and re-echoing through his consciousness. A shiver ran the length of his spine. That sound--that devilish sound.

He stood there, a tall, magnificently muscled man, stripped to the waist, sweating from the heat generated by the rockets that were decelerating the craft after its meteoric flight from Mars. Shuddering, he clenched his fists, and walked slowly back the way he had come.

The creature throbbed with the pull of him, a gnawing, writhing, tormenting struggle that pierced into the deeps of every restless, agitated cell, stabbing agonizingly along the alien nervous system; and then became terrifyingly aware of the inevitable, the irresistible need to take the shape of the life.

Parelli stopped uncertainly. The floor moved under him, a visible wave that reared brown and horrible before his incredulous eyes and grew into a bulbous, slobbering, hissing mass. A venomous demon head reared on twisted, half-human shoulders. Gnarled hands on apelike, malformed arms clawed at his face with insensate rage--and changed even as they tore at him.

"Good God!" Parelli bellowed.

The hands, the arms that clutched him grew more normal, more human, brown, muscular. The face assumed familiar lines, sprouted a nose, eyes, a red gash of mouth. The body was suddenly his own, trousers and all, sweat and all.

"--God!" his image echoed; and pawed at him with clutching fingers and an impossible strength.

Gasping, Parelli fought free, then launched one crushing blow straight into the distorted face. A drooling scream of agony came from the thing. It turned and ran, dissolving as it ran, fighting dissolution, uttering strange half-human cries.

And, struggling against horror, Parelli chased it, his knees weak and trembling from sheer funk and incredulity. His arm reached out, and plucked at the disintegrating trousers. A piece came away in his hand, a cold, slimy, writhing lump like wet clay.

The feel of it was too much. His gorge rising in disgust, he faltered in his stride. He heard the pilot shouting ahead:

"What's the matter?"

Parelli saw the open door of the storeroom. With a gasp, he dived in, came out a moment later, wild-eyed, an atom-gun in his fingers. He saw the pilot, standing with staring, horrified brown eyes, white face and rigid body, facing one of the great windows.

"There it is!" the man cried.

A gray blob was dissolving into the edge of the glass, becoming glass. Parelli rushed forward, atom-gun poised. A ripple went through the glass, darkening it; and then, briefly, he caught a glimpse of a blob emerging on the other side of the glass into the cold of space.

The officer stood gaping beside him; the two of them watched the gray, shapeless mass creep out of sight along the side of the rushing freight liner.

Parelli sprang to life. "I got a piece of it!" he gasped. "Flung it down on the floor of the storeroom."

It was Lieutenant Morton who found it. A tiny section of floor reared up, and then grew amazingly large as it tried to expand into human shape. Parelli with distorted, crazy eyes scooped it up in a shovel. It hissed; it nearly became a part of the metal shovel, but couldn't because Parelli was so close. Changing, fighting for shape, it slobbered and hissed as Parelli staggered with it behind his superior officer. He was laughing hysterically. "I touched it," he kept saying, "I touched it."

A large blister of metal on the outside of the space freighter stirred into sluggish life, as the ship tore into the Earth's atmosphere. The metal walls of the freighter grew red, then white-hot, but the creature, unaffected, continued its slow transformation into gray mass. Vague thought came to the thing, realization that it was time to act.

Suddenly, it was floating free of the ship, falling slowly, heavily, as if somehow the gravitation of Earth had no serious effect upon it. A minute distortion in its electrons started it falling faster, as in some alien way it suddenly became more allergic to gravity.

The Earth was green below; and in the dim distance a gorgeous and tremendous city of spires and massive buildings glittered in the sinking Sun. The thing slowed, and drifted like a falling leaf in a breeze toward the still-distant Earth. It landed in an arroyo beside a bridge at the outskirts of the city.

A man walked over the bridge with quick, nervous steps. He would have been amazed, if he had looked back, to see a replica of himself climb from the ditch to the road and start walking briskly after him.

Find the--greatest mathematician!

It was an hour later; and the pain of that throbbing thought was a dull, continuous ache in the creature's brain, as it walked along the crowded street. There were other pains, too. The pain of fighting the pull of the pushing, hurrying mass of humanity that swarmed by with unseeing eyes. But it was easier to think, easier to hold form now that it had the brain and body of a man.

Find--mathematician!

"Why?" asked the man's brain of the thing; and the whole body shook with startled shock at such heretical questioning. The brown eyes darted in fright from side to side, as if expecting instant and terrible doom. The face dissolved a little in that brief moment of mental chaos, became successively the man with the hooked nose who swung by, the tanned face of the tall woman who was looking into the shop window, the--

With a second gasp, the creature pulled its mind back from fear and fought to readjust its face to that of the smooth-shaven young man who sauntered idly in from a side street. The young man glanced at him, looked away, then glanced back again startled. The creature echoed the thought in the man's brain: "Who the devil is that? Where have I seen that fellow before?"

Half a dozen women in a group approached. The creature shrank aside as they passed, its face twisted with the agony of the urge to become woman. Its brown suit turned just the faintest shade of blue, the color of the nearest dress, as it momentarily lost control of its outer atoms. Its mind hummed with the chatter of clothes and "My dear, didn't she look dreadful in that awful hat?"

There was a solid cluster of giant buildings ahead. The thing shook its human head consciously. So many buildings meant metal; and the forces that held metal together would pull and pull at its human shape. The creature comprehended the reason for this with the understanding of the slight man in a dark suit who wandered by dully. The slight man was a clerk; the thing caught his thought. He was thinking enviously of his boss who was Jim Brender, of the financial firm of J. P. Brender & Co.

The overtones of that thought struck along the vibrating elements of the creature. It turned abruptly and followed Lawrence Pearson, bookkeeper. If people ever paid attention to other people on the street, they would have been amazed after a moment to see two Lawrence Pearsons proceeding down the street, one some fifty feet behind the other. The second Lawrence Pearson had learned from the mind of the first that Jim Brender was a Harvard graduate in mathematics, finance and political economy, the latest of a long line of financial geniuses, thirty years old, and the head of the tremendously wealthy J. P. Brender & Co. Jim Brender had just married the most beautiful girl in the world; and this was the reason for Lawrence Pearson's discontent with life.

"Here I'm thirty, too," his thoughts echoed in the creature's mind, "and I've got nothing. He's got everything--everything while all I've got to look forward to is the same old boardinghouse till the end of time."