Mae ignored him. She said to me, "If we go in," she said, "we'll have to set off thermite, and keep doing it all the way down to the chamber. I'm not sure we have enough thermite to do that."

"Maybe not," I said. I had a different concern. "We're wasting our time unless we destroy all the swarms, and all the assemblers that are making them. Right?" They both nodded.

"I'm not sure that'll be possible," I said. "I thought the swarms would be powered down at night. I thought we could destroy them on the ground. But they're not powered down-at least not all of them. And if just one of them gets past us, if it escapes from the cave…" I shrugged. "Then this has all been a waste of time."

"Right," Bobby said, nodding. "That's right. It'd be a waste of time."

Mae said, "We need some way to trap them in the cave."

"There isn't any way," Bobby said. "I mean, they can just fly out, whenever they want." Mae said, "There might be a way." She started rummaging in her backpack again, looking for something. "Meanwhile, the three of us better spread out."

"Why?" Bobby said, alarmed.

"Just do it," Mae said. "Now get moving."

I tightened my backpack, and adjusted the straps so it wouldn't rattle. I locked the night-vision goggles up on my forehead, and I started forward. I had gotten about halfway to the mound when I saw a dark figure climb out into the night.

I dropped down as quietly as I could. I was in a thick patch of sagebrush three feet high, so I was reasonably well concealed. I looked over my shoulder, but I didn't see either Mae or Bobby; they'd dropped to the ground, too. I didn't know if they'd separated yet. Cautiously, I pushed aside a plant in front of me, and looked toward the mound. The legs of the figure were silhouetted against the faint green glow. The upper body was black against the night stars. I flipped down the goggles, and waited a moment while they flared blue, and then saw the image resolve.

This time it was Rosie. Walking around in the night, looking in all directions, her body vigilant and alert. Except that she didn't move like Rosie, she moved more like a man. Then after a moment, the silhouette changed into Ricky. And it moved like Ricky. The figure crouched down, and appeared to be looking over the tops of the sage. I wondered what had brought it out of the mound. I didn't have to wait long to find out. Behind the figure, a white light appeared on the western horizon. It grew rapidly in brilliance, and soon I heard the thumping of helicopter blades. That would be Julia coming from the Valley, I thought. I wondered what was so urgent that she had had to leave the hospital against orders, and fly out here in the middle of the night.

As the helicopter approached, it switched on its searchlight. I watched the circle of blue-white light as it rippled over the ground toward us. The Ricky figure watched, too, then slid down out of sight.

And then the helicopter roared over me, blinding me for a moment in the halogen light. Almost immediately it banked sharply, and circled back.

What the hell was going on?

The helicopter made a slow arc, passing over the mound but not stopping, then coming to a stop right above where I was hiding. I was caught in the blue glow. I rolled onto my back and waved to the helicopter, pointing repeatedly toward the lab. I mouthed "Go!" and pointed away.

The helicopter descended, and for a moment I thought it was going to land right beside me. Then it abruptly banked again, and moved away low to the ground, heading south toward the concrete pad. The sound faded.

I decided I had better change my position fast. I got to my knees and in a crouch, moved crabwise thirty yards to the left. Then I dropped down again. When I looked back at the mound, I saw three-no, four figures coming out of the interior. They moved apart, each heading to a different area of the mound. They all looked like Ricky. I watched as they went down the slope of the mound, and moved out into the bush. My heart began to pound in my chest. One of the figures was coming in my direction. As it approached, I saw it veer off to the right. It was going to the place where I had been before. When it reached my last hiding place, it stopped, and turned in all directions. It was not far from me at all. I could see through the goggles that this new Ricky figure now had a complete face, and the clothing was much more detailed. In addition, this figure moved with the sensation of real body weight. It might be an illusion, of course, but I guessed that the swarm had increased mass, and now weighed fifty pounds, maybe more. Maybe twice that. If so, then the swarm now had enough mass to jolt you with a physical impact. Even knock you off your feet.

Through the goggles I saw the figure's eyes move, and blink. The surface of the face now had the texture of skin. The hair appeared to be composed of individual strands. The lips moved, the tongue licked nervously. All in all this face looked very much like Ricky-disturbingly like Ricky. When the head turned in my direction, I felt that Ricky was staring right at me. And I suppose it was, because the figure began to move directly toward me. I was trapped. My heart was thumping in my chest. I hadn't planned for this; I had no protection, no sort of defense. I could get up and run, of course, but there was nowhere to go. I was surrounded by miles of desert, and the swarms would hunt me down. In a few moments I would beWith a roar, the helicopter came back. The Ricky figure looked toward it as it came, and then turned and fled, literally flying over the ground, not bothering any longer to animate the legs and feet. It was creepy to see this human replica, suddenly floating over the desert. But the other three Ricky figures were running, too. Running hard, conveying a distinct sense of panic. Did the swarms fear the helicopter? It seemed they did. And as I watched, I understood why. Even though the swarms were now heavier and more substantial, they were still vulnerable to strong winds. The helicopter was a hundred feet in the air but the downdraft was powerful enough to deform the running figures, flattening them partially as they fled. It was as if they were being hammered down.

The figures vanished into the mound.

I looked back at Mae. She was standing up in the streambed now, talking on her radio to the helicopter. She'd needed that radio, all right. She yelled to me, "Let's go!" and began running toward me. I was dimly aware of Bobby, running away from the mound, back to his ATV. But there was no time to worry about him. The helicopter hung poised right above the mound itself. Dust whipped up, stinging my eyes.

Then Mae was beside me. Removing our goggles, we pulled on our oxygen masks. She turned me, twisted the tank valve behind me. I did the same for her. Then we put the night goggles back on. It seemed like a lot of contraptions jiggling and rattling around my face. She clipped a halogen flashlight to my belt, and another to her own. She leaned close, shouted: "Ready?"

"I'm ready!"

"Okay, let's go!"

There was no time to think. It was better that way. The helicopter downdraft roared in my ears. Together we clawed our way up the slope of the mound, our clothes whipping around us. We arrived at the edge, barely visible in the thick swirling dust. We couldn't see anything beyond the rim. We couldn't see what was below.

Mae took my hand, and we jumped.