I walked up to him and touched his shoulder. He turned toward me with a halfway expectant expression. His eyes were bottomless. He studied my face for a puzzled moment, then-not finding anything-started to turn away.

"Wait," I said. He turned back. "What's your name?" He blinked at me. "Your name?" I repeated.

His mouth began to work. "Nay-nay-nay ... ?" he said. He was trying to imitate my sounds. He smiled at the noises he made. "Nay-nay-nay-nay-nay-nay-" he repeated.

I put my hands on his shoulders. I looked into his eyes, trying to create a sense of relationship through eye contact. The boy tried to look away-I pulled his face back to mine and stared into his eyes again. "No. Stay with me," I said firmly.

He blinked at me uncertainly. "Who are you?" I asked him.

"Bub," he said.

"Bub? Bob?"

"Bub-bub-bub-" He smiled happily. "Bub-bub-bub-bub-"

"No," I said. "No." I pulled his face back to mine again. "No-no-no..." he said. "No-no-no...." And then, "Bub-bub-bub ... bub-bub-bub. . . . "

I let go of his shoulders and let him wander away, still bubbling. I turned back to Fletcher. "All right. What?"

She shook her head. "Uh uh. Keep going."

This time, I chose a little girl. She was wearing only a pair of panties. What was it about these people and clothing anyway? She was very thin, very underdeveloped. She could have been a boy.

I stopped her and looked into her face. She was as blank as the others.

"Who are you?" I asked. "What's your name?"

"My name... ?" she said. "My name?" She blinked. Like the boy, her expression was uncertain and puzzled.

"That's right. What's your name?"

"My name, my name ... is Auntie Mame. My game is fame, my game, my name, my name-" She babbled happily at me, smiling with delight at the sound of her own words. She'd figured out the game. "The game is name is fame is lame-"

I let go of her and turned her back toward the crowd.

"All right," I said to Fletcher, "I got it. They're not zombies. You can interact with them. But they've lost most of their sense of speech, so they're not walking wounded either. They're an intermediate step. Is that all?"

"Part of it," she said.

"What is it?" I asked. "A plague effect? Brain burn fever?"

"Brain burn fever is fatal," Fletcher said grimly. "If this is a plague effect, it's something we can't identify. See that fellow there?" She pointed at a tall beefy man. "He used to be one of the sharpest biologists at the university. He was at the South Pole when the plagues broke out. He was never exposed. He was fully vaccinated before he returned. If it's a plague effect, it's a mental one."

"How did he ... end up here?" I asked.

She lowered her voice. "He was studying them-" She waved her hand to indicate the wandering bodies. "He thought he could see patterns of herding-something like the Emperor Penguins. He spent a lot of time living with them, moving among them. One day, he didn't come back. When we finally got worried, we came down here and found him wandering around with the rest of them. He couldn't talk much more than they could. He'd become one of them."

I thought about that. Before I could ask the question, Fletcher said, "We're not in any danger. It takes prolonged exposure."

"Oh," I said. I was not reassured.

There were several hundred bodies in the plaza now. I stood there for a moment, watching them, trying to figure out why they seemed so... interesting.

"There's something about them," I said. "I can't figure it out, but there's something going on here. The minute you look at them, you know that they're not normal. What is it?" I asked Fletcher. "What's the signal I'm picking up?"

"You tell me," she said. "Tell me what you see?"

"I see bodies. Pink bodies. That's part of it, isn't it? They don't wear much clothing."

"By summer, they'll all be naked-but that's not it either. San Francisco Plaza has seen crowds of naked bodies before. The average Freedom Day Festival has less clothing than this."

"I wouldn't know. My dad never let me come."

"Too bad. Anyway, nudity is only part of it. What else?"

"Um-their skin. When I touched them, their skin felt slick. Not quite oily. Kind of smooth. Different."

"Mm hm, but that's not the cue either. You don't go around touching people to see if they're different."

"Right." I studied the milling crowd again.

"I'll give you a hint," she said. "What's missing?"

"Missing? Mmmm. Talking. There's not a lot of talking. A few of them are babbling to themselves, but it's not loud and offensive, not like a street lady. They're babbling like babies amused with the sounds they're making-wait a minute." A thought was beginning to form. "What's missing is... intensity. They have a quality of innocence. They're like children, aren't they? It's as if they've given up all the stuff they've ever learned about how to be a grownup so they could go back to the innocence of children. Right?"

"Go on," she encouraged, but she was smiling. I was on the right track.

"They can feel pain or anger-but they don't carry it around with them. Adults do. We get hurt or angry and we carry it around with us for weeks, handing it out to everybody we meet. Did you ever watch Aroundabout on TV? One time they did nothing but photograph faces at random on a city street. Almost every single person they showed looked like they were wearing a mask. Their expressions were all pinchy and tight. But these ... people-I guess that's what I should call them-these people, their faces are relaxed. They've given up the pain-"

I realized something else and shut up suddenly. "What was that?" Fletcher asked.

"Um, nothing really. I was just realizing how sad it must be to have to give up your intelligence to be free from pain." I looked at her. Her face was hurting with the same realization. Her eyes were moist. "Is this what you wanted me to see?"

"Oh, no," she said. She swallowed and looked uncomfortable. "It hasn't even started yet."

I LOOKED at the bodies again. "This is a herd, isn't it?"

"Mm hm," she said. "Last summer, it numbered over twelve hundred. During the winter, it fell to about three. Now it's building up again. We've got about seven fifty here. This is the largest herd in Northern California."

"What happened to the others?"

"Most of them died," she said noncommittally. "A few wander off every night. The pattern is this: you go from shock to being one of the walking wounded. There's hope for the walking wounded. But only if you get quick treatment. Otherwise, you just keep sinking.

"There's an instinct at work here. People seek out crowds, activity. So, this-" she pointed, "-is inevitable. The walking wounded gather in herds. I guess it's an illusion of safety. Some of them, though, are so far gone they can't even survive in a herd. Dropouts become zombies. The life expectancy of a zombie is six weeks. I'm surprised it's that long."

I looked at her. "You've been studying this, haven't you?"

She nodded. "You may be looking at the future of the human race. At the rate this herd is growing, we could hit twenty-five hundred by July. If that happens, we expect it to split into two herds." She pointed across the plaza. "See those two trucks over there? Those are the-you should pardon the expression-cowboys. They keep the herd under control. We used to keep the herd at Golden Gate Park, but we were losing too many every night, so we moved them down here. We can put them to bed in Brooks Hall."

The noon sun was getting warmer. I noticed that more and more of the herd members were discarding what little clothing they wore.

Fletcher followed my glance. "Yeah," she said. "It happens. We used to have a couple little old ladies who did nothing but follow the herd around putting their clothes back on them. There's one of them now. She finally gave up."