Lightning

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."
    "I might never have been born," Chris said.
    She reached to Chris and put a hand on his arm, not only to reassure him but to reassure herself of his current solidity. "I might not have been born myself. Everything I've seen, the good and bad of the world that's been since 1944… it'll all wash away like an elaborate sandcastle, and a new reality will exist in its place."
    "A new and worse reality," Stefan said, clearly exhausted by the effort he had made to explain what was at stake.
    "In that new world, I might never have written my novels."
    "Or if you wrote novels," Stefan said, "they would be different from those you've done in this life, grotesque works produced by an artist laboring under the rule of an oppressive government, in the iron fist of Nazi censorship."
    "If those guys build the atom bomb in 1944," Chris said, "then we'll all just crumble into dust and blow away."
    "Not literally. But like dust, yes," Stefan Krieger agreed. "Gone, with no trace that we've ever been."
    "We've gotta stop them," Chris said.
    "If we can," Stefan agreed. "But first we've got to stay alive in
this
reality, and that might not be easy."
    Stefan needed to relieve himself, and Laura helped him into the motel bathroom, handling him as if she were a nurse accustomed to matter-of-fact dealings with the plumbing of sick men. By the time she returned him to the bed, she was worried about him again; though he was muscular, he felt limp, clammy, and he was frighteningly weak.
    She told him briefly about the shoot-out at Brenkshaw's, through which he had remained comatose. "If these assassins are coming from the past instead of the future, how do they know where to find us? How did they know in 1944 that we'd be at Dr. Brenkshaw's when we were, forty-five years later?"
    "To find you," Stefan said, "they made two trips. First, they went farther into the future, a couple of days farther, to this coming weekend perhaps, to see if you had shown up anywhere by then. If you hadn't—and apparently you had not—then they started checking the public record. Back issues of newspapers, for one thing. They looked for the stories about the shooting at your house last night, and in those stories they read that you'd taken a wounded man to Brenkshaw's place in San Bernardino. So they simply returned to '44 and made a second trip—this time to Dr. Brenkshaw's in the early hours of this morning, January 11."
    "They can hopscotch around us," Chris told Laura. "They can pop ahead in time to see where we show up, then they pick and choose the easiest place along the time stream to ambush us. It's sorta like… if we were cowboys and the Indians were all psychic."

    "Who was Kokoschka?" Chris wanted to know. "Who was the man who killed my dad?"
    "Head of institute security," Stefan said. "He