It was dark. Terribly dark. But the infrared filter clicked into place, and the darkness vanished. The metal shape moved forward, easing through the kitchen, its treads half-retracted for greatest quiet. It came to the back door and halted, listening.

There was no sound. The house was still. They were all asleep upstairs. Sound asleep.

The Nanny pushed, and the back door opened. It moved out onto the porch, letting the door close gently behind it. The night air was thin and cold. And full of smells, all the strange, tingling smells of the night, when spring has begun to change into summer, when the ground is still moist and the hot July sun has not had a chance to kill all the little growing things.

The Nanny went down the steps, onto the cement path. Then it moved cautiously onto the lawn, the wet blades of grass slapping its sides. After a time it stopped, rising up on its back treads. Its front part jutted up into the air. Its eye stalks stretched, rigid and taut, waving very slightly. Then it settled back down and continued its motion forward.

It was just going around the peach tree, coming back toward the house, when the noise came.

It stopped instantly, alert. Its side doors fell away and its grapples ran out their full lengths, lithe and wary. On the other side of the board fence, beyond the row of shasta daisies, something had stirred. The Nanny peered, clicking filters rapidly. Only a few faint stars winked in the sky overhead. But it saw, and that was enough.

On the other side of the fence a second Nanny was moving, making its way softly through the flowers, coming toward the fence. It was trying to make as little noise as possible. Both Nannies stopped, suddenly unmoving, regarding each other—the green Nanny waiting in its own yard, the blue prowler that had been coming toward the fence.

The blue prowler was a larger Nanny, built to manage two young boys. Its sides were dented and warped from use, but its grapples were still strong and powerful. In addition to the usual reinforced plates across its nose there was a gouge of tough steel, a jutting jaw that was already sliding into position, ready and able.