Free Time's Eye by Arthur C. Clarke, Stephen Baxter

was confident, if edgy with fatigue.
    As the evening wore on, he took to following her around, puppylike.
    It had been a long day—the longest of Bisesa’s life, she said, even if she had lost a few hours—and Captain Grove’s advice that the newcomers should be allowed to eat and rest seemed wise. But they insisted they had work to do before resting. Abdikadir wanted to check on Casey, the other pilot. And he wanted to return to the machine they called their “Little Bird.” “I have to erase the memory banks of the electronic gear,” he said. “There’s sensitive data in there, especially the avionics . . .” Josh was entranced by this talk of intelligent machines, and he imagined the air full of invisible telegraph wires, transmitting mysterious and important messages hither and yon.
    Grove was inclined to allow the request. “I can’t see how we can be harmed by allowing the destruction of what I don’t understand anyhow,” he said dryly. “And besides—you say it is your duty, Warrant Officer. I respect that. Time and space may flow like toffee, but duty endures.”
    For her part Bisesa wanted to retrace the track her helicopter had taken, she said, before the crash. “We were shot down. I think that was just
after
we noticed the sun dancing around the sky. So—you see? If we’ve somehow come through some, some
barrier in time
, then whoever shot at us must be on this side too . . .”
    Grove thought this jaunt would be better left until morning, for he could see Bisesa’s fatigue as well as Josh could. But Bisesa didn’t want to stop moving—not yet—as if to stop would be to accept the extraordinary reality of the situation. So Grove approved the mission. Josh’s respect for the man’s judgment and compassion grew; Grove understood what was going on here no better than anybody else, but he was clearly trying to deal with the simple human needs of the people who had, literally, fallen out of the sky into his domain.
    A field party was drawn together: Bisesa, with Josh and Ruddy, both of whom insisted on accompanying her, and a small squad of privates under the nominal command of the Geordie private Batson, who, it seemed, might have impressed Grove enough that day to earn a promotion.
    By the time they set out from the fort the dark was gathering. The soldiers carried oil lamps and burning torches. They walked directly east from the site of the chopper’s crash. Bisesa had estimated the distance at no more than a mile.
    The lights of the fort receded, and the Frontier dusk opened up around them, huge and empty. But Josh could see thick black mounds of cloud on every horizon.
    He hurried beside Bisesa. “If it is true—”
    “What?”
    “This business of slipping through time—you, and the man-ape creatures—how do you think it can have happened?”
    “I’ve no idea. And I’m not sure if I’d rather be a castaway in time or a victim of a nuclear war. Anyhow,” she said briskly, “how do you know
you’re
not the castaway?”
    Josh quailed. “I never thought of that. You know, I can scarcely believe I am even holding this conversation! If you had told me this morning that before I slept this night I would see a flying machine powerful enough to carry people inside it—and that those people would, and plausibly too, claim to be from a future a century and a half hence—I would have thought you were insane!”
    “But if it’s true,” Ruddy said insistently, jogging alongside them—never very fit, he was panting a little—“if it’s true, there’s so much you know, so much you could tell us! For
our
future is
your
past.”
    She shook her head. “I’ve seen too many movies. Have you never heard of the chronology protection conjecture?”
    Josh was baffled, as was Ruddy.
    Bisesa said, “I guess you don’t even know what a movie is, let alone know
Terminator
. . . Look—some people think that if you go back in time and change something, so that the future you came from