Stony-faced, she said, "That was completely unnecessary."

I saw Ricky looking at me thoughtfully. As if he was trying to decide something. Bobby turned his back while he cooked, as if he was embarrassed by a marital spat. Had they gotten to Bobby? I thought I saw a thin black line at his neck, but I couldn't be sure, and I didn't dare stare.

"Unnecessary?" I said, full of outrage. "Those people were my friends. And they were your friends, Ricky. And yours, Bobby. And I don't want to hear this celebration shit anymore!" I turned and stomped out of the room. As I left, Vince was coming in. "Better take it easy, pal," Vince said. "You'll give yourself a stroke."

"Fuck off," I said.

Vince raised his eyebrows. I brushed past him.

"You're not fooling anybody, Jack!" Julia called after me. "I know what you're really up to!"

My stomach flipped. But I kept walking.

"I can see right through you, Jack. I know you're going back to her."

"Damn right!" I said.

Was that what Julia really thought? I didn't believe it for a moment. She was just trying to mislead me, to keep me off guard until… what? What were they going to do? There were four of them. And only two of us-at least, there were two if they hadn't already gotten to Mae.

Mae wasn't in the biology laboratory. I looked around and saw that a side door was ajar, leading downstairs to the underground level where the fermentation chambers were installed. Up close, they were much larger than I had realized, giant stainless spheres about six feet across. They were surrounded by a maze of pipes and valves and temperature control units. It was warm here, and very noisy.

Mae was standing by the third unit, making notes on a clipboard and shutting a valve. She had a rack of test tubes at her feet. I went down and stood beside her. She looked at me, then shot a glance toward the ceiling, where a security camera was mounted. She walked around to the other side of the tank, and I followed her. Over here, the tank blocked the camera. She said, "They slept with the lights on."

I nodded. I knew what it meant, now.

"They're all infected," she said.

"Yes."

"And it's not killing them."

"Yes," I said, "but I don't understand why."

"It must have evolved," she said, "to tolerate them."

"That fast?"

"Evolution can happen fast," she said. "You know the Ewald studies." I did. Paul Ewald had studied cholera. What he found was that the cholera organism would quickly change to sustain an epidemic. In places where there were no sanitary water supplies but perhaps a ditch running through a village, the cholera was virulent, prostrating the victim and killing him where he fell from massive overwhelming diarrhea. The diarrhea contained millions of cholera organisms; it would run into the water supply and infect others in the village. In this way the cholera reproduced, and the epidemic continued.

But when there was sanitary water supply, the virulent strain could not reproduce. The victim would die where he fell but his diarrhea would not enter the water supply. Others would not be infected, and the epidemic would fade. Under those circumstances, the epidemic evolved to a milder form, enabling the victim to walk around and spread the milder organisms by contact, dirty linens, and so on.

Mae was suggesting that the same thing had happened to the swarms. They had evolved to a milder form, which could be transmitted from one person to another. "It's creepy," I said.

She nodded. "But what can we do about it?"

And then she began to cry silently, tears running down her cheeks. Mae was always so strong. Seeing her upset unnerved me now. She was shaking her head. "Jack, there's nothing we can do. There's four of them. They're stronger than we are. They're going to kill us the way they killed Charley."

She pressed her head against my shoulder. I put my arm around her. But I couldn't comfort her. Because I knew she was right.

There was no way out.

Winston Churchill once said that being shot at focused the mind wonderfully. My mind was going very fast now. I was thinking that I had made a mistake and I had to fix it. Even though it was a typically human mistake.

Considering that we live in an era of evolutionary everything-evolutionary biology, evolutionary medicine, evolutionary ecology, evolutionary psychology, evolutionary economics, evolutionary computing-it was surprising how rarely people thought in evolutionary terms. It was a human blind spot. We looked at the world around us as a snapshot when it was really a movie, constantly changing. Of course we knew it was changing but we behaved as if it wasn't. We denied the reality of change. So change always surprised us. Parents were even surprised by the maturing of their own children. They treated them as younger than they really were. And I had been surprised by the change in the evolution of the swarms. There was no reason why the swarms shouldn't evolve in two directions at the same time. Or three, or four, or ten directions, for that matter. I should have anticipated that. I should have looked for it, expected it. If I had, I might be better prepared to deal with the situation now. But instead I had treated the swarm as one problem-a problem out there, in the desert-and I had ignored other possibilities.

It's called denial, Jack.

I started to wonder what else I was denying now. What else I had failed to see. Where did I go wrong? What was the first clue I had missed? Probably the fact that my initial contact with a swarm had produced an allergic reaction-a reaction that almost killed me. Mae had called it a coliform reaction. Caused by a toxin from the bacteria in the swarm. That toxin was obviously the result of an evolutionary change in the E. coli that made up the swarm. Well, for that matter, the very presence of phage in the tank was an evolutionary change, a viral response to the bacteria that"Mae," I said. "Wait a minute."

"What?"

I said, "There might be something we can do to stop them."

She was skeptical; I could see it in her face. But she wiped her eyes and listened.

I said, "The swarm consists of particles and bacteria, is that right?"

"Yes…"

"The bacteria provide the raw ingredients for the particles to reproduce themselves. Right? Okay. So if the bacteria die, the swarm dies too?"

"Probably." She frowned. "Are you thinking of an antibiotic? Giving everyone an antibiotic? Because you need a lot of antibiotics to clear an E. coli infection, they'd have to take drugs for several days, and I don't-"

"No. I'm not thinking of antibiotics." I tapped the tank in front of me. "I'm thinking of this."

"Phage?"

"Why not?"

"I don't know if it will work," she said. She frowned. "It might. Except… how're you going to get the phage into them? They won't just drink it down, you know."

"Then we'll fill the atmosphere with it," I said. "They'll breathe it in and they'll never know."

"Uh-huh. How do we fill the atmosphere?"

"Easy. Don't shut down this tank. Feed the bacteria into the system. I want the assembly line to start making virus-a lot of virus. Then we release into the air." Mae sighed. "It won't work, Jack," she said.

"Why not?"

"Because the assembly line won't make a lot of virus."

"Why not?"

"Because of the way the virus reproduces. You know-the virus floats around, attaches to a cell wall, and injects itself into the cell. Then it takes over the cell's own RNA, and converts it to making more viruses. The cell ceases all its normal metabolic functions, and just cranks out viruses. Pretty soon the cell is packed with viruses, and it bursts like a balloon. All the viruses are released, they float to other cells, and the process starts all over."

"Yes… so?"

"If I introduce phage into the assembly lines, the virus will reproduce rapidly-for a while. But it will rupture a lot of cell membranes, leaving behind all those membranes as a lipid crud. The crud will clog the intermediate filters. After about an hour or two, the assembly lines will start to overheat, the safety systems will kick in, and shut everything down. The whole production line will just stop. No virus."