Lightning

the way to the bottom."
    He went down the wall of the arroyo, pulled most of the way by the force of gravity but having to scoot along a couple of times when friction stopped him. It was exactly the kind of daredevil stunt that would have raised a mother's ire under other circumstances, but now she cheered him on.
    She pumped at least a hundred rounds into the Toyota, hoping to pierce the fuel tank and set off the gasoline with a bullet-made spark, roasting the bastards as they huddled against the far side. But she emptied the magazine without the desired result.
    When she stopped shooting, they took a crack at her. She did not stay long enough to give them a target. With the second Uzi held before her in both hands, she sat on the edge of the arroyo and shoved off into the slide that Chris had already used. In seconds she was at the bottom.
    Dry tumbleweeds had blown down to the floor of the gulch from the desert above. Gnarled driftwood, some time-grayed lumber washed from the distant ruins of an old desert shack, and a few stones littered the powder-soft soil that formed the bed of the arroyo. None of those things offered a place to hide or protection from the gunfire that would soon be directed down at them. "Mom?" Chris said, Meaning: What now? The arroyo would have scores of tributaries spread out across the desert, and many of those tributaries would have tributaries of their own. The drainage network was like a maze. They could not hide in it forever, but perhaps by putting a few branches of the system between themselves and their pursuers, they would gain time to plan an ambush.
    She said, "Run, baby. Follow the main arroyo, take the first right-hand branch you come to, and wait there for me."
    "What're you going to do?"
    "I'll wait for them to look over the edge up there," she said, pointing to the top of the palisades, "then pick them off if I can. Now go,
go
." He ran. Leaving the canister of Vexxon in plain sight, Laura returned to the wall of the arroyo down which they'd slid. She went to a different vertical channel, however, one that was carved deeper into the wall, had less of a slope, and was half-blocked at its midpoint by a mesquite bush. She stood in the bottom of that deep hollow, confident that the bush overhead blocked their view of her from the desert above.
    To the east, Chris vanished around a turn into a tributary of the main channel.
    A moment later she heard voices. She waited, waited, giving them time to feel confident that both she and Chris were gone. Then she stepped out from the erosion channel in the arroyo wall, turned, and swept the top of the cliff with bullets.
    Four men were there, peering down, and she killed the first two, but the third and fourth leaped backward, out of sight before the arc of fire reached them. One of the bodies lay at the top of the arroyo wall, one arm and leg over the brink. The other fell all the way to the floor of the channel, losing his sunglasses on the way.

    March 16, 1944. The institute.
    When the bottle with the message did not bounce back to him, Stefan was reasonably confident that it had reached Laura before she had been killed, only seconds after he had first departed for 1944.
    Now he returned to the programmer's desk and set to work on the calculations that would return him to the desert a few minutes
after
his previous arrival there. He could make that trip because he would be arriving subsequent to his previous hasty departure, and there would be no possibility of encountering himself, no paradox.
    Again the calculations were not terribly difficult because he needed only to work forward from the numbers that the IBM PC had provided him. Though he knew that the time he spent here was not passing in equal measure in the desert of 1989, he was eager to rejoin Laura nevertheless. Even if she had taken the advice of the message in the bottle, even if the future he had seen had been changed and she was still alive, she would have to deal with those SS gunmen, and she would need help.
    In forty minutes he had the numbers that he required, and he reprogrammed the gate.
    Again he opened the panel on the jaunt recorder and tore the evidence off that spool of paper.
    Carrying the Uzi and the pistol, gritting his teeth as the dull throbbing in his half-healed shoulder grew worse, he entered the gate.

    Lugging both the Vexxon canister and the Uzi, Laura joined Chris in the narrower tributary off the main channel, about sixty feet from the point at