“He can tell us that much, anyway, Mom.” To the wounded man, Chris said, “When do you come from?” He stared at Chris, then at Laura, and the haunted look was in his eyes again.

“When do you come from? Huh? The year 2100? 3000?”

In his paper-dry voice, her guardian said, "Nineteen forty-four.

The little bit of activity had clearly tired him already, for his eyelids looked heavy, and his voice was fainter than it had been, so Laura was certain that he had lapsed into delirium again.

“When?” Chris repeated, baffled by the answer he had been given.

“Nineteen forty-four.”

“That's impossible,” Chris said.

“Berlin,” her guardian said.

“He's delirious,” Laura told Chris.

His voice was slurred now as weariness dragged him down, but what he said was unmistakable: “Berlin.”

“Berlin?” Chris said. “You mean-Berlin, Germany?” Sleep claimed the wounded man, not the unnatural sleep of a coma but restful sleep that was immediately marked by soft snoring, though in the moment before he slipped away, “Nazi Germany.” he said,

One Life to Live was on the television, but neither she nor Chris was paying any attention to the soap opera. They had drawn the two chairs closer to the bed, where they could watch the sleeping man. Chris was dressed, and his hair was mostly dry, though it remained damp at the nape of his neck. Laura felt grimy and longed for a shower, but she was not going to leave her guardian in case he woke again and was able to talk. She and the boy spoke in whispers:

“Chris, it just occurred to me, if these people were from the future, why wouldn't they have been carrying laser guns or something futuristic when they came for us?”

“They wouldn't want everyone to know they were from the future,” Chris said. “They'd bring weapons and wear clothes that wouldn't be out of place here. But, Mom, he said he was from-”

“I know what he said. But it doesn't make sense, does it? If they had time travel in 1944, we'd know about it by now, wouldn't we?”

At one-thirty her guardian woke and seemed briefly confused as to his whereabouts. He asked for more water, and Laura helped him drink. He said he was feeling a little better, though very weak and still surprisingly sleepy. He asked to be propped up higher. Chris got the two spare pillows from the closet and helped his mother raise the wounded man.

“What is your name?” Laura asked. “Stefan. Stefan Krieger.”

She repeated the name softly, and it was all right, not melodic but solid, a masculine-sounding name. It was just not the name of a guardian angel, and she was mildly amused to realize that after so many years, including two decades during which she had professed to have no belief in him. she still expected his name to be musical and unearthly.

“And you really come from-”

“Nineteen forty-four,” he repeated. Just the effort required to move to a sitting position had wrung fine beads of perspiration from his brow-or perhaps the sweat resulted in part from thoughts of the time and place where his long journey had begun. “Berlin, Germany. There was a brilliant Polish scientist, Vladimir Penlovski, considered a madman by some, and very likely mad in fact - very mad, I think - but also a genius. He was in Warsaw, working on certain theories about the nature of time for more than twenty-five years before Germany and Russia collaborated to invade Poland in 1939...”

Penlovski, according to Stefan Krieger, was a Nazi sympathizer and welcomed Hitler's forces. Perhaps he knew that from Hitler he would receive the kind of financial backing for his researches that he could not get from sources more rational. Under the personal patronage of Hitler himself, Penlovski and his closest assistant, Wladyslaw Januskaya, went to Berlin to establish an institute for temporal research, which was so secret that it was given no name. It was simply called the institute. There, in association with German scientists no less committed and no less farsighted than he, financed by a seemingly inexhaustible river of funds from the Third Reich, Penlovski had found a way to pierce the artery of time and move at will through that bloodstream of days and months and years."

“Blitzstrasse,” Stefan said.

“Blitz-that part of it means lightning,” Chris said. “Like Blitzkrieg-lightning war-in all those old movies.”

Lightning Road in this case,“ Stefan said. ”The road to the future."

It literally could have been called Zukunftstrasse, or Future Road, Stefan explained, for Vladimir Penlovski had been unable to send men backward in time from the gate he had invented. They could travel only forward, into their future, and automatically return to their own era.

There seems to be some cosmic mechanism that prohibits time travelers from meddling with their own pasts in order to change their present day circumstances. You see, if they could travel back in time to their own past, there would develop certain-"

“Paradoxes!” Chris said excitedly.

Stefan looked surprised to hear the boy speak that word.

Smiling, Laura said, “As I told you, we've had rather a long discussion about your possible origins, and time travel turned out to be the most logical. And in Chris here, you're looking at my resident expert on the weird.”

“Paradox,” Stefan agreed. “It's the same word in English and German. If a time traveler could go back in time to his own past and affect some event in history, that change would have tremendous ramifications. It would alter the future from which he had come. Therefore he wouldn't be able to return to the same world he'd left-”

“Paradox!” Chris said gleefully.

“Paradox,” Stefan agreed. “Apparently nature abhors a paradox and generally will not permit a time traveler to create one. And thank God for that. Because . . . suppose, for example, Hitler sent an assassin back in time to kill Franklin Roosevelt and Winston Churchill long before they rose to high office, which would have resulted in the election of different men in the U.S. and England, men who might have been less brilliant and more easily dealt with, leading to Hitler's triumph by '44 or sooner.”

He was speaking now with a passion that his physical condition would not allow him to sustain, and Laura could see it taking a toll of him word by word. The perspiration had almost dried on his brow; but now, although he was not even gesturing, a new thin film of sweat silvered his pale forehead again. The circles of fatigue around his eyes appeared to grow darker. But she could not stop him and order him to rest, because she wanted and needed to hear everything he had to say-and because he would not have allowed her to stop him.

“Suppose der Fuhrer could send back assassins to kill Dwight Eisenhower, George Patton, Field Marshal Montgomery, kill them in their cradles, when they were babies, eliminating them and others, all the best military minds the Allies possessed. Then most of the world would have been his by '44, in which case time travelers would have been going back in time to kill those men who had already long been dead and posed no threat, Paradox, you see. And thank God that nature permits no such paradox, no such tampering with the time traveler's own past, for otherwise Adolf Hitler would have turned the entire world into a concentration camp, a crematorium.”

They were silent a while, as the possibility of such hell on earth struck each of them. Even Chris responded to the picture of an altered world that Stefan painted, for he was a child of the eighties, in which the villains of film and television melodramas were usually voracious aliens from a distant star or Nazis. The Swastika, the silver death's-head symbol and black uniforms of the SS, and that strange fanatic with the small mustache were to Chris especially terrifying because they were part of the media-created mythology on which he had been raised. Laura knew that real people and events, once subsumed by mythology, were somehow lone real to a child than the very bread he ate.

Stefan said, “So from the institute we could go only forward in time, but that had its uses too. We could leap forward a few decades discover if Germany had held on in the dark days of the war and had somehow turned the tide. But of course we found that Germany had not done any such thing, that the Third Reich had been defeated. Yet with all the knowledge of the future to draw from, could not that tide be turned, after all? Surely there were things Hitler could do to save the Reich even as late as '44. And there were things that might be brought back from the future with which the war might be won-”

“Such as,” Chris said, “atomic bombs!” “Or the knowledge of how they were built,” Stefan said. “The Reich already had a nuclear research program, you know, and if they'd had a breakthrough early enough, had split the atom ...” “They'd have won the war,” Chris said. Stefan asked for water and drank half a glass this time. He wanted to hold the glass in his good hand, but he was shaking too much; water slopped on the bedclothes, and Laura had to help him. When he spoke again, Stefan's voice wavered at times. “Because the time traveler exists outside of time during his journey, he is not only able to move in time but geographically, as well. Picture him hanging above the earth, unmoving, as the globe turns below him. That's not what he does, of course, but it's easier to see that image than to imagine him hovering in another dimension. Now, as he hangs above the world, it turns below him, and if his journey to the future is gauged properly, he can travel to a precise time at which he will find himself in Berlin, the same city he left years before. But if he chooses to travel a few hours more or less, the world will have turned that much more beneath him, and he will arrive at a different place on its surface. The calculations to achieve a precise arrival are monumentally difficult in my era, 1944-” “But they'd be easy these days,” Chris said, “with computers.”

Shifting in discomfort against the pillows that propped him up, putting his trembling right hand against his wounded left shoulder as if to quell the pain by his own touch, he said, “Teams of German physicists, accompanied by Gestapo, were sent secretly to various cities in Europe and the United States in the year 1985, to accumulate vital information on the making of nuclear weapons. The material they were after was not classified or difficult to find. With what they already knew from their own researches, they could obtain the rest from textbooks and scientific publications readily available at any major university library in '85. Four days before I departed the institute for the last time, those teams returned from '85 to March 1944, with material that would give the Third Reich a nuclear arsenal before the autumn of that year. They were to spend a few weeks studying the material at the institute before deciding how and where to introduce that knowledge into the German nuclear program without revealing bow it had been obtained. I knew then that I had to destroy the institute and everything it contained, key personnel as well as files, to prevent a future shaped by Adolf Hitler.”

As Laura and Chris listened rapt, Stefan Krieger told them how he had planted explosives in the institute how on the last of his days in '44 he had shot Penlovski, Januskaya, and Volkaw, and had programmed the time gate to bring him to Laura in present-day America.

But something had gone wrong at the last minute, as Stefan was leaving. The public power supply failed. The RAF had bombed Berlin far the first time in January that year, and the U.S. bombers had made die first daylight runs on March 6, so the power supply had been interrupted often, not merely due to bomb damage but also because of die work of saboteurs. It was to guard against such interruptions that the gate itself was powered by a secure generator. Stefan beard no bombers that day when, wounded by Kokoschka, he had crawled into the gate, so apparently the power failed because of saboteurs.

“And the timer on the explosives stopped. The gate was not destroyed. It's still open back there, and they can come after us. And . . . they can still win the war.”

Laura was getting another headache. She put her fingertips to her temples. “But wait. Hitler can't have succeeded in building atomic weapons and winning World War Two, because we don't live in a world where that happened. You don't have to worry. Somehow, in spite of all the knowledge they took back through the gate, they obviously failed to develop a nuclear arsenal.”

“No,” he said. “They've failed so far, but we can't assume they will continue to fail. To those men at the institute in Berlin in 1944, their past is immutable, as I have said. They cannot travel backward in time and change their own past. But they can change their future and ours, because a time traveler's future is mutable; he can take steps to alter it.”

“But his future is my past,” Laura said. “And if the past can't be changed, how can he change mine?” “Yeah,” Chris said. “Paradox.”

Laura said, “Listen, I haven't spent the last thirty-four years in a world ruled by Adolf Hitler and his heirs; therefore, in spite of the gate, Hitler failed.”

Stefan's expression was dismal. “If time travel were invented now, in 1989, that past of which you speak-World War Two and every event since-would be unalterable. You could not change it, for nature's rule against backward time-travel and time-travel paradoxes would apply to you. But time travel has not been discovered here-or rediscovered. The time travelers at the institute in Berlin in '44 are free to change their future, apparently, and though they will simultaneously be changing your past, nothing in the laws of nature will stop them. And there you have the greatest paradox of all-the only one that for some reason nature seems to allow.”

“You're saying they could still build nuclear weapons back then with the information they got in '85,” Laura said, “and win the war?”

“Yes. Unless the institute is destroyed first.” “And what then? Suddenly, all around us, we find things changed, find ourselves living under Nazism?”

“Yes. And you won't even know what's happened, because you will be a different person than you are now. Your entire past will never have occurred. You will have lived a different past altogether, and you will remember nothing else, none of what has happened to you in this life because this life will never have existed. You will think the world has always been as it is, that there was never a world in which Hitler lost.” What he was proposing terrified and appalled her because it made life seem even more fragile than she had always thought it was. The world under her feet suddenly seemed no more real than the world of a dream; it was apt to dissolve without warning and send her tumbling into a great, dark void.

With growing horror she said, “If they change the world in which I grew up, I might never have met Danny, never married.”