"Looks like Rosie is going into that mound," he said. "You mean we follow her there?"

"Yes," I said.

At Mae's suggestion, we walked the rest of the way. Lugging our backpacks, it took us the better part of ten minutes to reach the vicinity of the mound. We paused about fifty feet away. There was a nauseating smell in the air, a putrid odor of rotting and decay. It was so strong it made my stomach turn. Then too, a faint green glow seemed to be emanating from inside the mound.

Bobby whispered, "You really want to go in there?"

"Not yet," Mae whispered. She pointed off to one side. Rosie's body was moving up the slope of the mound. As she came to the rim, her rigid legs pointed into the air for a moment. Then her body toppled over, and she fell into the interior. But she stopped before she disappeared entirely; for several seconds, her head remained above the rim, her arm outstretched, as if she were reaching for air. Then, slowly, she slid the rest of the way down, and vanished. Bobby shivered.

Mae whispered, "Okay. Let's go."

She started forward in her usual noiseless way. Following her, I tried to be as quiet as I could. Bobby crunched and crackled his way along the ground. Mae paused, and gave him a hard look.

Bobby held up his hands as if to say, what can I do?

She whispered, "Watch where you put your feet."

He whispered, "I am."

"You're not."

"It's dark, I can't see."

"You can if you try."

I couldn't recall ever seeing Mae show irritation before, but we were all under pressure now. And the stench was terrible. Mae turned and once again moved forward silently. Bobby followed, making just as much noise as before. We had only gone a few steps before Mae turned, held up her hand, and signaled for him to stay where he was. He shook his head, no. He clearly didn't want to be left alone.

She gripped his shoulder, pointed firmly to the ground, and whispered, "You stay here."

"No…"

She whispered, "You'll get us all killed."

He whispered, "I promise."

She shook her head, pointed to the ground. Sit.

Finally, Bobby sat down.

Mae looked at me. I nodded. We set out again. By now we were twenty feet from the mound itself. The smell was almost overpowering. My stomach churned; I was afraid I might be sick. And this close, we began to hear the deep thrumming sound. More than anything it was that sound that made me want to run away. But Mae kept going.

We crouched down as we climbed the mound, and then lay flat along the rim. I could see Mae's face in the green glow coming from inside. For some reason the stench didn't bother me anymore. Probably because I was too frightened.

Mae reached into the side pouch of her pack, and withdrew a small thumb-sized camera on a thin telescoping stick. She brought out a tiny LCD screen and set it on the ground between us. Then she slid the stick over the rim.

On the screen, we saw a green interior of smooth undulating walls. Nothing seemed to be moving. She turned the camera this way and that. All we saw were green walls. There was no sign of Rosie.

Mae looked at me, pointed to her eyes. Want to take a look now?

I nodded.

We inched forward slowly, until we could look over the rim.

It wasn't what I expected at all.

The mound simply narrowed an existing opening that was huge-twenty feet wide or more, revealing a rock slide that sloped downward from the rim and ended at a gaping hole in the rock to our right. The green light was coming from somewhere inside this gaping hole. What I was seeing was the entrance to a very large cave. From our position on the rim, we couldn't see into the cave itself, but the thrumming sound suggested activity within. Mae opened the telescoping stick to its full length, and gently lowered the camera into the hole. Soon we could see farther into the cave. It was undoubtedly natural, and large: perhaps eight feet high, ten feet wide. The rock walls were pale white, and appeared to be covered with the milky substance we'd seen on Rosie.

And Rosie's body was only a short distance inside. We could see her hand sticking out around a bend in the rock wall. But we could see nothing beyond the bend. Mae signaled me: want to go down?

I nodded slowly. I didn't like how this felt, I didn't like that I had no idea what was beyond the bend. But we really had no choice.

She pointed back toward Bobby. Get him?

I shook my head, no. He wouldn't help us here.

She nodded, and started very slowly to slide out of her backpack, making no sound at all, when she suddenly froze. Literally froze: she didn't move a muscle. I looked at the screen. And I froze, too.

A figure had walked from behind the bend, and now stood alertly at the entrance of the cave, looking around.

It was Ricky. …

He was behaving as if he had heard a sound, or had been alerted for some other reason. The video camera still dangled down the rim of the mound. It was pretty small; I didn't know if he would see it.

I watched the screen tensely.

The camera didn't have good resolution and the screen was the size of my palm, but it was still clear that the figure was Ricky. I didn't understand what he was doing here-or even how he had gotten here. Then another man came around the bend.

He was also Ricky.

I glanced at Mae, but she remained utterly still, a statue. Only her eyes moved. I squinted at the screen. Within the limits of video resolution, the two figures appeared to be identical in every respect. Same clothes, same movements, same gestures and shrugs. I couldn't see the faces well, but I had the impression they were more detailed than before. They didn't seem to notice the camera.

They looked up at the sky, and then at the rock slide for a while, and then they turned their backs on us, and returned to the interior of the cave.

Still Mae did not move. She had been motionless for almost a minute already and in that time she hadn't even blinked. Now the men were gone, andAnother figure came around the corner. It was David Brooks. He moved awkwardly, stiffly at first, but he quickly became more fluid. I had the feeling I was watching a puppeteer perfect his moves, animating the figure in a more lifelike way. Then David became Ricky. And then David again. And the David figure turned and went away.

Still Mae waited. She waited fully two more minutes, and then finally withdrew the camera. She jerked her thumb, indicating we should go back. Together, we crept away from the rim, back down the mound, and moved away silently into the desert night. We gathered a hundred yards to the west, near our vehicles. Mae was rummaging in her backpack; she pulled out a clipboard with a felt marker. She flicked on her penlight and began to draw.

"This is what you're up against," she said. "The cave has an opening like this, which you saw. Past the bend, there's a big hole in the floor, and the cave spirals downward for maybe a hundred yards. That brings you into one large chamber that is maybe a hundred feet high, and a couple of hundred feet wide. Single big room, that's all. There are no passages leading off, at least none that I saw."

"That you saw?"

"I've been in there," she said, nodding.

"When?"

"A couple of weeks ago. Back when we first started looking for the swarm's hiding place. I found that cave and went in there in day-light. I didn't find any indication of a swarm then." She explained that the cave was filled with bats, the whole ceiling covered with them, packed together in a pink squirming mass, all the way out to the entrance. "Ugh," Bobby said. "I hate bats."

"I didn't see any bats there tonight."

"You think they've been driven away?"

"Eaten, probably."

"Jesus, guys," Bobby said, shaking his head. "I'm just a programmer. I don't think I can do this. I don't think I can go in there."