The pattern of Dr. Simon Cartwright's encephalic emanations, and the approximate position of the center of these emanations were impressed on its mind. And in a strangely bulbous ship it plunged outward from that eternally dark and silent planet towards Earth.

A man was walking along a road. A high road. A silent, dark road. Below him on both sides of the road flat marshland swept away, and a little wind caressed him with chill fingers. His tiny world of road beneath him, darkness around him, sky above him, contained only the sound of his footsteps—and one other. A regular, liquid sound. He thought it was a sound from the marsh. He listened to it, and wondered how long it had been with him. It was close behind him on the road. He stopped, turned round in small curiosity, and bellowed in great horror. He threw up his hands against an immense bulk, a frog-like shape, a lurching, flowing movement. Then it was upon him, and stilled his futile writhings, and passed over him, and left him dead.

The Assassin continued along the road. It was aware that it had killed, but it could not contemplate the fact. It possessed all the mental powers of its race, but its conditioning had focused them in one direction, the assassination of Dr. Cartwright. It could consider only those factors which had a direct relation to that purpose.

Daylight was one of those factors.

It was not aware of the passage of time, but when the sensitive patch on its back began to contract it left the road and went to the marsh. There it burrowed into the slime until green-flecked water closed over it. And deeper until a depth of mud protected it from the sun.

Dr. Cartwright groaned and sat up in bed. He silenced the ringing telephone by putting the receiver to his ear.

"Do you know what time it is?" he asked, aggrieved.

"Hello? Doctor Cartwright? This is the police."

"It is half-past seven," continued Simon. "For me, the middle of the night. I am in no fit state to measure a drunk's reactions."

"I'm sorry, sir, but there's been an accident. On the Waverton Highway. A man is dead, Inspector Andrews is in charge of the case."

"Inspector Andrews? Is mayhem suspected? Never mind, I'll get down there, right away."

He put the receiver down and got out of bed. His wife muttered something unintelligible and wrapped his share of the blankets round her. Simon went downstairs. He made a cup of coffee and drank it while he dressed. The engine of his car was cold, but his house was on a hill and he was able to coast down to the Highway.

The road was level and straight, and after a few minutes driving a little tableau came into sight—two cars, a group of uniforms. Inspector Andrews, tall, thin, dyspeptic, greeted him with a limp handshake. "Something funny about this," he said. "See what you think."

Simon went down on one knee beside the body and began to undo the clothing. After a time he looked up into the sky. "This is very strange," he murmured.

"I know," grunted Andrews. "Can they take the body now?"

Simon stood up and nodded. He remained staring out across the marsh until the body had been removed, and the ambulance a distant object. Then he went and sat in his car. Andrews finished giving instructions to his Sergeant, and joined him. "I'll let you give me breakfast," he said.

"You're very kind," said Simon absently, and released the brake.

"Any use asking for the cause of death?" asked Andrews.

"Oh, the cause of death was crushing, but the cause of the cause of death—" Simon shook his head. "There wasn't an unbroken bone in his body. Could he have been dropped from an airplane?"

Andrews shook a ponderous head. "He was a bus driver on his way to work without an enemy in the world. And I've a feeling his death is going to keep me awake at nights. Anyway, Sergeant Bennet is going over the area with a magnifying glass. We'll put up a pretty good show. Can you suggest anything?"

"It wasn't a car," said Simon carefully. "The skin was unbroken, except from the inside. I can only imagine something like a rubber-covered steam-roller."

hat night the Assassin killed two people.

When it grew dark it heaved itself up out of the slime. A long business of bodily expansion and contraction. Two men were on the road and heard the noise it made.

"Somethin' out there."

"Stray cow, maybe."

They stood and peered into the dark, trying to see a familiar shape. The Assassin approached them, and was too big for them to see. They stood in its path and looked for a familiar object in the blackness of its body. So the instant of apprehension was small, the panic and exertion soon over. Without pausing the Assassin moved over them and continued on its way.

A little later Inspector Andrews found them. He was in a radio patrol car, and he was moving in the same direction as the Assassin. With him in the car were three large men carrying automatic rifles. Andrews stopped the car, and one of the men got out and knelt by the bodies. Andrews watched him somberly for a moment then reached for the microphone. He spoke to the station sergeant.

"Inspector Andrews here. Send an ambulance out here, will you, and phone Doctor Cartwright. Tell him the steam-roller's loose again. It may be on the road heading his way. Yes, steam-roller. He'll understand."

He put the microphone down, called to the man on the road. "I'm leaving you here, Roberts. There's an ambulance on its way. Go back with it. Get in Sergeant Bennet's car and both of you join us up ahead."

He closed the car window and released the brake. The empty road began to unwind slowly into the area of light ahead.

Simon put the receiver down and looked at his wife. She was concentrating on a sock by the fire. He went over and kissed the top of her head. "Goodbye," she said.

"Listen," he said quietly. "When I'm gone lock the door behind me and don't go out. If you hear any funny noises go down to the cellar. Understand?"

She was a little frightened. "Honey, what is it?"

He smiled. "It's nothing. Long John Andrews is out hunting. I'm going along in case he shoots himself."

He took his shot-gun off the mantle and stuffed his pockets with cartridges.

"I'll bring you back a rabbit," he said. "So long."

He drove down slowly. He was scared, but he was still young enough to find it exhilarating. The loaded shot-gun was a great help.

He turned on to the highway, and slowed to walking pace. He stared into the darkness ahead until his eyes burned, and imagination peopled his surroundings with writhing shapes.

Then he saw it, and the muscles across his chest trembled convulsively. Fear clutched his stomach. He slammed his foot down on the brake and gaped up at it. It was standing still in the middle of the road, a giant, pear shaped body, looking something like a man kneeling upright. At the front, turned inwards, were a number of arm-like appendages.

The shot-gun was ridiculous now, the car made of paper. To get out and run was impossible, and he longed to be able to sit still and do nothing. And the seconds dragged by. Time for contemplation built up, and a strange realization dropped into his seething mind. He sensed something about its attitude. A cringing, a withdrawal. "God," he whispered. "It doesn't like the light."

He might have relaxed then, but it moved. One of its arms unfolded, swung outward holding something metallic. Simon yelled. He grabbed the shot-gun, shoved the door catch down, threw his weight sideways. He landed on his shoulder and kept on rolling. He reached the other side of the road, straightened up, and saw the roof of the car fly off with a roar. He fired then, from a crouching position and without taking aim. A lucky shot that hit the end of the weapon arm and shattered it. Then he ran, and the Assassin followed.

He ran in the direction he'd been heading, and gave himself up to terror. He was primaeval man fleeing from sabre-tooth. He was living a nightmare. His brain reeled, air burnt his lungs, and his pounding heart echoed in his temples. Then he was running into a blaze of light, between headlights that enfolded him like a mother's arms, and he was clinging to a radiator cap. Dimly he heard the crash of high powered rifles about him. A black figure came into his haven of light, began to loosen his tie.

"Get out of the light," he gasped. "It doesn't like the light."

"Who invited you?" grunted Andrews. He put Simon's arm round his neck, and half carried him round to the side of the car, pushed him into the front seat.

"I'll be all right in a minute," said Simon.

"Yeah," said Andrews, and left him.

After a little while the trembling in his limbs began to subside, breathing became easier. He leaned forward and watched a strange battle. The Assassin was about seventy yards ahead, moving slowly nearer. Two men stood on the right hand side of the car, pumping bullets into the grey, indistinct mass. Andrews stood watching with his hands in his jacket pockets. Suddenly he said, "All right, let go. You're only wasting bullets."

Simon looked at him in alarm. "Hey, you're not just going to stand there. It doesn't like the light, but light can't kill it."

"Lie down on the floor," said Andrews dourly, without looking at him.

"Eh?"

Andrews ignored him, stepped two paces forward. The Assassin was about twenty yards away now, seeming to have to fight against the stream of light. Andrews took his hands from his pockets. Simon saw what he was holding, and dived for the floor. He clasped his hands over the back of his neck as the night exploded with a gigantic crash.

When his ears had stopped screaming he got up. Andrews, an elbow on the window ledge, was watching him expressionlessly.

"You might have left me something to dissect," complained Simon. "Somebody's got to, you know."

"I'll mop you up a sponge full," said Andrews.

"Oh, no, you won't. You and your men stay back here. It's probably crawling with alien bacteria."

Actually, quite a lot of the Assassin was left, but decomposition was very rapid. Simon did the best he could with a magnifying glass and a penknife. He found that the body was almost entirely composed of bone and flesh in a honey-comb like structure. The bone being highly flexible, and the cavities filled with grey flesh. Flesh which quickly liquified and drained away from the bone. There was no blood, and Simon could find no trace of internal organs.

While he worked two more cars drove up, and gave him a little more light, but soon he had to give up. As he walked slowly back a spotlight sprang suddenly to life, and a pleasant authoritative voice spoke.

"Will you stay where you are, please, Doctor Cartwright."

Simon obeyed. Hell, he thought wearily. Officialdom has arrived. He shaded his eyes against the light, but he could see nothing.

"Who's that?" he asked.

"Commanding officer in charge of operations in this emergency. You've made an examination?"

"As far as I could. There's complete decomposition now."

"Oh, I see." A slight pause, then; "Perhaps I'd better put you in the picture. This is armed aggression, Doctor Cartwright. In any language it says war. Do you understand? We're at war, now.

"We found the vessel your friend came in several days ago. It was in the sea, twenty miles from here. Its discovery was kept secret because we weren't sure of its point of origin. Our people are engaged in finding the method of propulsion. They say it will give us the ability to travel in space. They also say that they can find the approximate position of its home planet. All that is top priority, of course, but in the meanwhile we must have an emergency line of defence against these things. We want to know how to find them and how to destroy them with the least possible expenditure of life and material. You understand?"

"Yes. I've got an idea about light waves. I fired a shot at it back there. The bone structure—"

"Don't tell me," interrupted the voice sharply. "Remember it. You realize, Doctor Cartwright, that you are just about the most important man alive. You know how fast it can move. You have fought it, you have examined it. So you can be sure that very good care will be taken of you."

"What are you saying?"

"I'm sorry, but you must see that you have to go into strict quarantine now. We dare not risk a plague. After quarantine you will go to work with our people. Now will you please get into the car at the extreme right, and follow the police."

"Where am I going?"

"Please hurry. There is a team of incendiaries waiting to clear the area."

"Oh, damnation," sighed The Most Important Man Alive, and walked towards the waiting car.

hen the ruler consulted the prognosticator again, after the Assassin's failure had been recorded, he found that a qualification had been added. The prophecy was now being fulfilled. He considered this dispassionately. He visualised the complex pattern of implication almost with pleasure. Was the machine alive? Certainly it could contemplate itself. It had calculated the effect of its existence, and had used the knowledge to destroy them. Or had they condemned themselves? By losing the ability to question. For the information on which the prophecy was based could have been available to them. Or was the machine only obeying a greater Fate? A Decree, stating that any life-form that surrendered itself to the dictates of a machine was doomed.

One thing alone was left to him. A choice. Without haste he began the preliminaries to thinking himself to death.