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

Mae and Charley rushed across the room to look out the window. David and Rosie stood and peered out the window above the sink. And I started to shout: "No, no! Get away from the windows!"

"What?"

"It's visual, remember? Get away from the windows!"

There was no good place to hide in the storage room, not really. Rosie and David crawled under the sink. Charley pushed in beside them, ignoring their protests. Mae slipped into the shadows of one corner of the room, easing herself into the space where two shelves didn't quite meet. She could only be seen from the west window, and then not easily. The radio crackled. "Hey guys?" It was Ricky. "One's heading for you. And uh… No… two others are joining it."

"Ricky," I said. "Go off air."

"What?"

"No more radio contact."

"Why?"

"Off, Ricky."

I dropped down on my knees behind a cardboard carton of supplies in the main room. The carton wasn't large enough to hide me entirely-my feet stuck out-but like Mae, I wasn't easily seen. Someone outside would have to look at an angle through the north window to see me. In any case, it was the best I could do.

From my crouched position, I could just see the others huddled beneath the sink. I couldn't see Mae at all, unless I really stuck my head around the corner of the carton. When I did, she looked quiet, composed. I ducked back and waited.

I heard nothing but the hum of the air conditioner.

Ten or fifteen seconds passed. I could see the sunlight streaming in through the north window above the sink. It made a white rectangle on the floor to my left. My headset crackled. "Why no contact?"

"Jesus fucking A," Charley muttered.

I put my finger to my lips, and shook my head.

"Ricky," I said, "don't these things have auditory capacity?"

"Sure, maybe a little, but-"

"Be quiet and stay off."

"But-"

I reached for the transmitter at my belt, and clicked it off. I signaled the others beneath the sink. They each turned their transmitters off.

Charley mouthed something to me. I thought he mouthed, "That fucking guy wants us killed."

But I couldn't be sure.

We waited.

It couldn't have been more than two or three minutes, but it seemed forever. My knees began to hurt on the hard concrete floor. Trying to get more comfortable, I shifted my position cautiously; by now I was sure the first swarm was in our vicinity. It hadn't appeared at the windows yet, and I wondered what was taking so long. Perhaps as it followed our path it had paused to inspect the cars. I wondered what swarm intelligence would make of an automobile. How puzzling it must look to that high-resolution eye. But maybe because the cars were inanimate, the swarm would ignore them as some sort of large, brightly colored boulders. But still… What was taking so long?

My knees hurt more with every passing second. I changed my position, putting weight on my hands and raising my knees like a runner at the blocks. I had a moment of temporary relief. I was so focused on my pain that I didn't notice at first that the glaring white rectangle on the floor was turning darker at the center, and spreading out to the sides. In a moment the entire rectangle turned dull gray.

The swarm was here.

I wasn't certain, but I fancied that beneath the hum of the air conditioner was a deep thrumming sound. From my position behind the crate, I saw the window above the sink grow progressively darker from swirling black particles. It was as if there was a dust storm right outside. Inside the shed it was dark. Surprisingly dark.

Underneath the sink, David Brooks began to moan. Charley clapped his hand over his mouth. They looked upward, even though the sink blocked their view of the window above them. And then the swarm vanished from the window, as quickly as it had come. Sunlight poured in again.

Nobody moved.

We waited.

Moments later, the window in the west wall turned dark, in the same way. I wondered why the swarm didn't enter. The window wasn't airtight. The nanoparticles could slide through the cracks without difficulty. But they didn't even seem to try. Perhaps this was an instance where network learning was on our side. Perhaps the swarms had been trained by their experience at the lab to think doors and windows were impermeable. Maybe that's why they weren't trying.

The thought gave me a hopeful feeling that helped counteract the pain in my knees. The west window was still dark, when the north window over the sink turned dark again. Now two swarms were looking in at the same time. Ricky had said there were three coming toward the building. He hadn't mentioned the fourth. I wondered where the third swarm was. A moment later, I knew.

Like a silent black mist, nanoparticles began to come into the room underneath the west door. Soon more particles entered, all around the door frame. Inside the room, the particles appeared to spin and swirl aimlessly, but I knew they would self-organize in a few moments. Then at the north window, I saw more particles flooding through the cracks. Through the air-conditioning vents in the ceiling, still more particles rushed downward. There was no point in waiting any longer. I got to my feet and stepped from my hiding place. I shouted for everybody to come out of hiding. "Form up in two rows!" Charley grabbed the Windex spray bottle and fell into line, grumbling, "What do you think our fucking chances are?"

"The best they'll ever get," I said. "Reynolds rules! Form up and stay with me! Let's go-now!"

If we weren't so frightened, we might have felt ridiculous, shuffling back and forth across the room in a tight cluster, trying to coordinate our movements-trying to imitate a flock of birds. My heart was pounding in my chest. I heard a roaring sound in my ears. It was hard to focus on our steps. I knew we were awkward, but we got better quickly. When we came to a wall, we wheeled and headed back again, moving in unison. I started swinging my arms and clapping with each step. The others did the same. It helped our coordination. And we each fought our terror. As Mae said later, "It was step aerobics from hell." And all the time, we watched the black nanoparticles as they came hissing into the room through cracks in doors and windows. It seemed to go on for a long time, but it was probably only thirty or forty seconds. Soon a kind of undifferentiated fog filled the room. I felt pinpricks all over my body, and I was sure the others felt it, too. David started moaning again, but Rosie was right beside him, encouraging him, urging him to keep it together. Suddenly, with shocking speed the fog cleared, the particles coalescing into two fully formed columns that now stood directly before us, rising and falling in dark ripples. Seen this close, the swarms exuded an unmistakable sense of menace, almost malevolence. Their deep thrumming sound was clearly audible, but intermittently I heard an angry hiss, like a snake.

But they did not attack us. Just as I had hoped, the programming deficits worked for us. Confronted by a cluster of coordinated prey, these predators were stymied. They did nothing at all.

At least for now.

Between claps, Charley said, "Do you believe-this fucking shit-it's working!" I said, "Yes but maybe-not for long." I was worried about how long David could control his anxiety. And I was worried about the swarms. I didn't know how long they'd just stand there before they innovated new behavior. I said, "I suggest we-move toward that-back door behind us-and get the hell out."

As we wheeled away from the wall, I angled slightly toward the rear room. Clapping and stepping in unison, our group moved away from the swarms, which thrummed deeply and followed.

"And if we get outside, then what?" David whined. He was having trouble staying in sync with the rest of us. In his panic, he kept stumbling. He was sweating and blinking rapidly. "We continue this way-flocking this way-back to the lab-and get inside-are you willing to try?"