'He's not allowed to remove them for any reason. We know exactly where we'll find what we want. There's only one place the papers can be.'

'Their security precautions play right into our hands.'

'Exactly,' Ryan murmured.

Ryan and Kastner slipped down the hillside, running between the trees. The ground was hard and cold underfoot. They emerged at the edge of the town. A few people were already up, moving slowly along the street. The town had not been bombed. There was no damage, as yet. The windows of the stores had been boarded up and huge arrows pointed to the underground shelters.

'What do they have on?' Kastner said. 'Some of them have something on their faces.'

'Bacteria masks. Come on.' Ryan gripped his blast pistol as he and Kastner made their way through the town. None of the people paid any attention to them.

'Just two more uniformed people,' Kastner said.

'Our main hope is surprise. We're inside the wall of defense. The sky is patrolled against Soviet craft. No Soviet agents could be landed here. And in any case, this is a minor research lab, in the center of the United States. There would be no reason for Soviet agents to come here.'

'But there will be guards.'

'Everything is guarded. All science. All kinds of research work.'

The school house loomed up ahead of them. A few men were milling around the doorway. Ryan's heart constricted. Was Schonerman one of them?

The men were going inside, one by one. A guard in helmet and uniform was checking their badges. A few of the men wore bacteria masks, only their eyes visible. Would he recognize Schonerman? What if he wore a mask? Fear gripped Ryan suddenly. In a mask Schonerman would look like anyone else.

Ryan slipped his blast pistol away, motioning Kastner to do the same. His fingers closed over the lining of his coat pocket. Sleep-gas crystals. No one this early would have been immunized against sleep-gas. It had not been developed until a year or so later. The gas would put everyone for several hundred feet around into varying periods of sleep. It was a tricky and unpredictable weapon - but perfect for this situation.

'I'm ready,' Kastner murmured.

'Wait. We have to wait for him him.'

They waited. The sun rose, warming the cold sky. More research workers appeared, filing up the path and inside the building. They puffed white clouds of frozen moisture and slapped their hands together. Ryan began to become nervous. One of the guards was watching him and Kastner. If they became suspicious- A small man in a heavy overcoat and horn-rimmed gla.s.ses came up the path, hurrying toward the building.

Ryan tensed. Schonerman! Schonerman flashed his badge to the guard. He stamped his feet and went inside the building, stripping off his mittens. It was over in a second. A brisk young man, hurrying to get to his work. To his papers.

'Come on,' Ryan said.

He and Kastner moved forward. Ryan pulled the gas crystals loose from the lining of his pocket. The crystals were cold and hard in his hand. Like diamonds. The guard was watching them coming, his gun alert. His face was set. Studying them. He had never seen them before. Ryan, watching the guard's face, could read his thoughts without trouble.

Ryan and Kastner halted at the doorway. 'We're from the FBI,' Ryan said calmly.

'Identify yourselves.' The guard did not move.

'Here are our credentials,' Ryan said. He drew his hand out from his coat pocket. And crushed the gas crystals in his fist.

The guard sagged. His face relaxed. Limply, his body slid to the ground. The gas spread. Kastner stepped through the door, peering around, his eyes bright.

The building was small. Lab benches and equipment stretched out on all sides of them. The workers lay where they had been standing, inert heaps on the floor, their arms and legs out, their mouths open.

'Quick.' Ryan pa.s.sed Kastner, hurrying across the lab. At the far end of the room Schonerman lay slumped over his bench, his head resting against the metal surface. His gla.s.ses had fallen off. His eyes were open, staring. He had taken his papers out of the drawer. The padlock and key were still on the bench. The papers were under his head and between his hands.

Kastner ran to Schonerman and s.n.a.t.c.hed the papers up, stuffing them into his briefcase.

'Get them all!'

'I have them all.' Kastner pulled open the drawer. He grabbed the remaining papers in the drawer. 'Every one of them.'

'Let's go. The gas will dissipate rapidly.'

They ran back outside. A few sprawled bodies lay across the entrance, workers who had come into the area.

'Hurry.'

They ran through the town, along the single main street. People gaped at them in astonishment. Kastner gasped for breath, holding on tight to his briefcase as he ran. 'I'm - winded.'

'Don't stop.'

They reached the edge of the town and started up the hillside. Ryan ran between the trees, his body bent forward, not looking back. Some of the workers would be reviving. And other guards would be coming into the area. It would not be long before the alarm would be out.

Behind them a siren whirred into life.

'Here they come.' Ryan paused at the top of the hill, waiting for Kastner. Behind them men were swelling rapidly into the street, coming up out of underground bunkers. More sirens wailed, a dismal echoing sound.

'Down!' Ryan ran down the hillside toward the time ship, sliding and slipping on the dry earth. Kastner hurried after him, sobbing for breath. They could hear orders being shouted. Soldiers swarming up the hillside after them.

Ryan reached the ship. He grabbed Kastner and pulled him inside. 'Get the hatch shut. Get it closed!'

Ryan ran to the control board. Kastner dropped his briefcase and tugged at the rim of the hatch. At the top of the hill a line of soldiers appeared. They made their way down the hillside, aiming and firing as they ran.

'Get down,' Ryan barked. Sh.e.l.ls crashed against the hull of the ship. 'Down!'

Kastner fired back with his blast pistol. A wave of flame rolled up the hillside at the soldiers. The hatch came shut with a bang. Kastner spun the bolts and slid the inner lock into place. 'Ready. All ready.'

Ryan threw the power switch. Outside, the remaining soldiers fought through the flame to the side of the ship. Ryan could see their faces through the port, seared and scorched by the blast.

One man raised his gun awkwardly. Most of them were down, rolling and struggling to rise. As the scene dimmed and faded he saw one of them crawling to his knees. The man's clothing was on fire. Smoke billowed from him, from his arms and shoulders. His face was contorted with pain. He reached out, toward the ship, reaching up at Ryan, his hands shaking, his body bent.

Suddenly Ryan froze.

He was still staring fixedly when the scene winked out and there was nothing. Nothing at all. The meters changed reading. Across the time map the arms moved calmly, tracing their lines.

In the last moment Ryan had looked directly into the man's face. The pain-contorted face. The features had been twisted, screwed up out of shape. And the horn-rimmed gla.s.ses were gone. But there was no doubt - It was Schonerman.

Ryan sat down. He ran a shaking hand through his hair.

'You're certain?' Kastner said.

'Yes. He must have come out of the sleep very quickly. It reacts differently on each person. And he was at the far end of the room. He must have come out of it and followed after us.'

'Was he badly injured?'

'I don't know.'

Kasner opened his briefcase. 'Anyhow, we have the papers.'

Ryan nodded, only half hearing. Schonerman injured, blasted, his clothing on fire. That had not been part of the plan.

But more important - had it been part of history? had it been part of history?

For the first time the ramification of what they had done was beginning to emerge in his mind. Their own concern had been to obtain Schonerman's papers, so that USIC could make use of the artificial brain. Properly used, Schonerman's discovery could have great value in aiding the restoration of demolished Terra. Armies of workerrobots replanting and rebuilding. A mechanical army to make Terra fertile again. Robots could do in a generation what humans would toil at for years. Terra could be reborn.

But in returning to the past had they introduced new factors? Had a new past been created? Had some kind of balance been upset?

Ryan stood up and paced back and forth.

'What is it?' Kastner said. 'We got the papers.'

'I know.'

'USIC will be pleased. The League can expect aid from now on. Whatever it wants. This will set up USIC forever. After all, USIC will manufacture the robots. Workerrobots. The end of human labor. Machines instead of men to work the ground.'

Ryan nodded. 'Fine.'

'Then what's wrong?'

'I'm worried about our continuum.'

'What are you worried about?'

Ryan crossed to the control board and studied the time map. The ship was moving back toward the present, the arms tracing a path back. 'I'm worried about new factors we may have introduced into past continuums. There's no record of Schonerman being injured. There's no record of this event. It may have set a different causal chain into motion.'

'Like what?'

'I don't know. But I intend to find out. We're going to make a stop right away and discover what new factors we've set into motion.'

Ryan moved the ship into a continuum immediately following the Schonerman incident. It was early October, a little over a week later. He landed the ship in a farmer's field outside of Des Moines, Iowa, at sunset. A cold autumn night with the ground hard and brittle underfoot.

Ryan and Kastner walked into town, Kastner holding tightly onto his briefcase. Des Moines had been bombed by Russian guided missiles. Most of the industrial sections were gone. Only military men and construction workers still remained in the city. The civilian population had been evacuated.

Animals roamed around the deserted streets, looking for food. Gla.s.s and debris lay everywhere. The city was cold and desolate. The streets were gutted and wrecked from the fires following the bombing. The autumn air was heavy with the decaying smells of vast heaps of rubble and bodies mixed together in mounds at intersections and open lots.

From a boarded-up newsstand Ryan stole a copy of a news magazine, Week Review Week Review. The magazine was damp and covered with mold. Kastner put it into his briefcase and they returned to the time ship. Occasional soldiers pa.s.sed them, moving weapons and equipment out of the city. No one challenged them.

They reached the time ship and entered, locking the hatch behind them. The fields around them were deserted. The farm building had been burned down, and the crops were withered and dead. In the driveway the remains of a ruined automobile lay on its side, a charred wreck. A group of ugly pigs nosed around the remains of the farmhouse, searching for something to eat.

Ryan sat down, opened the magazine. He studied it for a long time, turning the damp pages slowly.

'What do you see?' Kastner asked.

'All about the war. It's still in the opening stages. Soviet guided missiles dropping down. American disc bombs showering all over Russia.'

'Any mention of Schonerman?'

'Nothing I can find. Too much else going on.' Ryan went on studying the magazine. Finally, on one of the back pages, he found what he was looking for. A small item, only a paragraph long.

SOVIET AGENTS SURPRISED.

A group of Soviet agents, attempting to demolish a Government research station at Harristown, Kansas, were fired on by guards and quickly routed. The agents escaped, after attempting to slip past the guards into the work offices of the station. Pa.s.sing themselves off as FBI men, the Soviet agents tried to gain entry as the early morning shift was beginning work. Alert guards intercepted them and gave chase. No damage was done to the research labs or equipment. Two guards and one worker were killed in the encounter. The names of the guards Ryan clutched the magazine.

'What is it?' Kastner hurried over.

Ryan read the rest of the article. He laid down the magazine, pushing it slowly toward Kastner.

'What is it?' Kastner searched the page.

'Schonerman died. Killed by the blast. We killed him. We've changed the past.'

Ryan stood up and walked to the port. He lit a cigarette, some of his composure returning. 'We set up new factors and started a new line of events. There's no telling where it will end.'

'What do you mean?'

'Someone else may discover the artificial brain. Maybe the shift will rectify itself. The time flow will resume its regular course.'

'Why should it?'

'I don't know. As it stands, we killed him and stole his papers. There's no way the Government can get hold of his work. They won't even know it ever existed. Unless someone else does the same work, covers the same material-'

'How will we know?'

'We'll have to take more looks. It's the only way to find out.'

Ryan selected the year 2051.

In 2051 the first claws had begun to appear. The Soviets had almost won the war. The UN was beginning to bring out the claws in the last desperate attempt to turn the tide of the war.

Ryan landed the time ship at the top of a ridge. Below them a level plain stretched out, criss-crossed with ruins and barbed wire and the remains of weapons.

Kastner unscrewed the hatch and stepped gingerly out onto the ground.

'Be careful,' Ryan said. 'Remember the claws.'

Kastner drew his blast gun. 'I'll remember.'

'At this stage they were small. About a foot long. Metal. They hid down in the ash. The humanoid types hadn't come into existence, yet.'

The sun was high in the sky. It was about noon. The air was warm and thick. Clouds of ash rolled across the ground, blown by the wind.

Suddenly Kastner tensed. 'Look. What's that? Coming along the road.'

A truck b.u.mped slowly toward them, a heavy brown truck, loaded with soldiers. The truck made its way along the road to the base of the ridge. Ryan drew his blast gun. He and Kastner stood ready.