"Oh jeez," he moaned. "It's so far… I don't know if…" He stumbled again, nearly lost his balance. And he wasn't clapping with the rest of us. I could almost feel his terror, his overwhelming urge to flee.

"David you stay with us-if you go on your own-you'll never make it-are you listening?" David moaned, "I don't know… Jack… I don't know if I can…" He stumbled again, bumped into Rosie, who fell against Charley, who caught her and pulled her back to her feet. But our flock was knocked into momentary disarray, our coordination gone. Immediately, the swarms turned dense black, coiled and tightened, as if ready to spring. I heard Charley whisper "Oh fuck," under his breath, and indeed, for a moment I thought he was right, and that it was all over.

But then we regained our rhythm, and immediately the swarms rose up, returned to normal. Their dense blackness faded. They resumed their steady pulsing. They followed us into the next room. But still they did not attack. We were now about twenty feet from the back door, the same door we had come in. I started to feel optimistic. For the first time, I thought it was possible we really might make it.

And then, in an instant, everything went to hell. …

David Brooks bolted.

We were well into the back room, and about to work our way around the freestanding shelves in the center of the room, when he ran straight between the swarms and past them, heading for the far door.

The swarms instantly spun and chased him.

Rosie was screaming for him to come back, but David was focused on the door. The swarms pursued him with surprising speed. David had almost reached the door-his hand was reaching for the doorknob-when one swarm sank low, and spread itself across the floor ahead of him, turning it black.

The moment David Brooks reached the black surface, his feet shot out from under him, as if he had stepped on ice. He howled in pain as he slammed onto the concrete, and immediately tried to scramble to his feet again, but he couldn't get up; he kept slipping and falling, again and again. His eyeglasses shattered; the frames cut his nose. His lips were coated with swirling black residue. He started to have trouble breathing.

Rosie was still screaming as the second swarm descended on David, and the black spread across his face, onto his eyes, into his hair. His movements became increasingly frantic, he moaned pitifully like an animal, yet somehow, as he slid and tumbled on hands and knees, he managed to make his way toward the door. At last he lunged upward, grabbed the doorknob, and managed to pull himself to his knees. With a final desperate movement, he twisted the knob, and kicked the door open as he fell.

Hot sunlight flared into the shed-and the third swarm swirled in from outside.

Rosie cried, "We've got to do something!" I grabbed her arm as she ran past me toward David. She struggled in my grip. "We have to help him! We have to help him!"

"There's nothing we can do."

"We have to help him!"

"Rosie. There's nothing we can do."

David was now rolling on the ground, black from head to toe. The third swarm had enveloped him. It was difficult to see through the dancing particles. It looked as though David's mouth was a dark hole, his eyeballs completely black. I thought he might be blind. His breath came in ragged gasps, with little choking sounds. The swarm was flowing into his mouth like a black river.

His body began to shudder. He clutched at his neck. His feet drummed on the floor. I was sure he was dying.

"Come on, Jack," Charley said. "Let's get the fuck out of here."

"You can't leave him!" Rosie shouted. "You can't, you can't!" David was sliding out the door, into the sunlight. His movements were less vigorous now; his mouth was moving, but we heard only gasps.

Rosie struggled to get free.

Charley grabbed her shoulder and said, "God damn it, Rosie-"

"Fuck you!" She wrenched free from his grip, she stamped on my foot and in my moment of surprise I let go, and she sprinted across the shed into the next room, shouting "David! David!" His hand, black as a miner's, stretched toward her. She grabbed his wrist. And in the same moment she fell, slipping on the black floor just as he had done. She kept saying his name, until she began to cough, and a black rim appeared on her lips.

Charley said, "Let's go, for Christ's sake. I can't watch."

I felt unable to move my feet, unable to leave. I turned to Mae. Tears were running down her cheeks. She said: "Go."

Rosie was still calling out David's name as she hugged him, pulled his body to her chest. But he didn't seem to be moving on his own anymore.

Charley leaned close to me and said, "It's not your fucking fault."

I nodded slowly. I knew what he was saying was true.

"Hell, this is your first day on the job." Charley reached down to my belt, flicked my headset on. "Let's go."

I turned toward the door behind me.

And we went outside.

Beneath the corrugated roof, the air was hot and still. The line of cars stretched away from us. I heard the whirr of a video camera motor up by the roof. Ricky must have seen us coming out on the monitors. Static hissed in my headset. Ricky said, "What the hell's going on?"

"Nothing good," I said. Beyond the line of shade, the afternoon sun was still bright.

"Where are the others?" Ricky said. "Is everybody okay?"

"No. Everybody is not."

"Well tell me-"

"Not now." In retrospect, we were all numb from what had happened. We didn't have any reaction except to try and get to safety.

The lab building stood across the desert a hundred yards to our right. We could reach the power station door in thirty or forty seconds. We set off toward it at a brisk jog. Ricky was still talking, but we didn't answer him. We were all thinking about the same thing: in another half a minute we would reach the door, and safety.

But we had forgotten the fourth swarm.

"Oh fuck," Charley said.

The fourth swarm swirled out from the side of the lab building, and started straight toward us. We stopped, confused. "What do we do?" Mae said, "Flock?"

"No." I shook my head. "There's only three of us." We were too small a group to confuse a predator. But I couldn't think of any other strategy to try. All the predator-prey studies I had ever read began to play back in my head. Those studies agreed on one thing. Whether you modeled warrior ants or Serengeti lions, the studies confirmed one major dynamic: left to their own devices, predators would kill all the prey until none remained-unless there was a prey refuge. In real life the prey refuge might be a nest in a tree, or an underground den, or a deep pool in a river. If the prey had a refuge, they'd survive. Without a refuge, the predators would kill them all.

"I think we're fucked," Charley said.

We needed a refuge. The swarm was bearing down on us. I could almost feel the pinpricks on my skin, and taste the dry ashen taste in my mouth. We had to find some kind of shelter before the swarm reached us. I turned full circle, looking in all directions, but there was nothing I could see, except"Are the cars locked?"

My headset crackled. "No, they shouldn't be."

We turned and ran.

The nearest car was a blue Ford sedan. I opened the driver's door, and Mae opened the passenger side. The swarm was right behind us. I could hear the thrumming sound as I slammed the door shut, as Mae slammed hers. Charley, still holding the Windex spray, was trying to open the rear passenger door, but it was locked. Mae twisted in the seat to unlock the door, but Charley had already turned to the next car, a Land Cruiser, and climbed inside. And slammed the door.

"Yow!" he said. "Fucking hot!"