Lightning

rounds, all of which pierced the woman, killing her instantly.
    "We could have questioned her," Corporal Bracher said. "About Krieger, about what he was doing here—"
    "She was paralyzed," Klietmann said impatiently. "She could feel nothing. I kicked her in the side, must've broken half her ribs, and she didn't even cry out. You can't torture information from a woman who can feel no pain."

    March 16, 1944. The institute.
    His heart hammering like a blacksmith's sledge, Stefan jumped down from the gate and ran to the programming board. He pulled the list of computer-derived numbers from his pocket and spread it out on the small programmer's desk that filled a niche in the machinery.
    He sat in the chair, picked up a pencil, pulled a tablet from the drawer. His hands shook so badly that he dropped the pencil twice. He already had the numbers that would put him in that desert five minutes after he had first left it. He could work backward from those figures and find a new set that would put him in the same place four minutes and fifty-five seconds earlier, only five seconds after he had originally left Laura and Chris.
    If he was gone only five seconds, the SS assassins would not yet have killed her and the boy by the time Stefan returned. He would be able to add his firepower to the fight, and perhaps that would be enough to change the outcome.
    He had learned the necessary mathematics when first assigned to the institute in the autumn of 1943. He could do the calculations. The work was not impossible because he didn't have to begin from scratch; he had only to refine the computer's numbers, work backward a few minutes.
    But he stared at the paper and could not
think
because Laura was dead and Chris was dead.
    Without them he had nothing.
    You can get them back, he told himself. Damn it, shape up. You can stop it before it happens.
    He bent himself to the task, working for nearly an hour. He knew that no one was likely to come to the institute so late at night and discover him, but he repeatedly imagined that he heard footsteps in the ground-floor hall, the
click-click-click
of SS boots. Twice he looked toward the gate, half convinced he had heard the five dead men returning from a.d. 6,000,000,000, somehow revitalized and in search of nim.
    When he had the numbers and doubled-checked them, he entered them in the board. Carrying the submachine gun in one hand and the pistol in the other, he climbed into the gate and passed through the point of transmission—
    —and returned to the institute.
    He stood for a moment in the gate, surprised, confused. Then he stepped through the energy field again—
    —and returned to the institute.
    The explanation hit him with such force that he bent forward as if he actually had been punched in the stomach. He could
not
go back earlier now, for he had already showed up at that place five minutes after leaving it; if he went back now he would be creating a situation in which he would surely be there to see himself arrive the first time. Paradox! The mechanism of the cosmos would not permit a time traveler to encounter himself anywhere along the time stream; when such a jaunt was attempted, it invariably failed. Nature despised a paradox.
    In memory he could hear Chris in the sleazy motel room where they had first discussed time travel: "Paradox! Isn't this wild stuff, Mom? Isn't this wild? Isn't this great?" And the charming, excited, boyish laughter.
    But there had to be a way.
    He returned to the programming board, dropped the guns on the work desk, and sat down.
    Sweat was pouring off his brow. He blotted his face on his shirt-sleeves.
    Think.
    He stared at the Uzi and wondered if he could send
that
back to her at least. Probably not. He had been carrying the machine gun and the pistol when he had returned to her the first time, so if he sent either of the guns back four minutes and fifty seconds earlier, they would exist twice in the same place when he showed up just four minutes and fifty seconds later. Paradox.
    But maybe he could send her something else, something that came from this room, something he had not been carrying with him and that would not, therefore, create a paradox.
    He pushed the guns aside, picked up a pencil, and wrote a brief message on a sheet of tablet paper:THE SS WILL KILL YOU AND CHRIS IF YOU STAY AT THE CAR. GET AWAY, HIDE, He paused, thinking. Where could they hide on that flat desert plain? He wrote: maybe in THE ARROYO. He tore the sheet of paper