"She just started walking." Alice told them, pushing tears across her cheeks with the flat of her hand. "I don't know if she went to Superior, or up to the city, or where she went."

Mack walked in from his room and stood quietly against the bookcase, listening.

"Is she going back to Portland?" asked Leigh.

"She didn't say anything."

"Maybe she had a family issue. Like, her mom."

"She would have told me if her mom wasn't good."

"She's been acting strange," Kyle explained. His voice did not communicate empathy.

Aviva stared straight down at her feet, her brightly tattooed arms balanced on her knees. While Alice had been Rae's roommate, Aviva was her closest friend. She was clearly shaken.

"Let's go find her," John suggested, standing. He ran his hand along his crew-cut white hair, and waited. "We can check the motels around here. The bus station. She's probably still walking to Superior." There was some agreement here; people started to rise.

Then Mack dropped a book on the floor. It hit the ground with unexpected force.

"She didn't leave because she wanted to."

The room turned sharply to him.

"Who would leave here on their own?" Mack asked them, his nasal voice low and calm. He watched members of Happy Trails consider this. Caleb saw the muscle of Aviva's jaw tighten and release.

"Anyone hazard, you know, a guess?"

Kyle raised his hand.

Mack pointed a finger at him. "My boy."

"She was expelled?"

"Absolutely."

The room held its breath.

"Was it because she didn't want to run Yosemite?" Makailah asked.

"That's part of it. But that was a symptom. There was a root disease. She didn't like it here anymore."

"She loved it," Aviva muttered to herself.

"She was ill."

People sat straight, surprised.

"What's wrong with her?" June whispered.

Mack stepped closer to the circle. "Rae was infected with a virus. The virus of negativity. I asked her to partic.i.p.ate in killing this virus, to use her kinetic energy against it, but she refused." He looked around the room, making eye contact with each one of them. "What I ask you guys to do matters. Every run, every private energy session, everything goes toward the collective kinetic energy of our house. We can't have one person refusing to partic.i.p.ate. Creating stasis."

Caleb stole a glance at Lily, in June's arms. Rae had spent a lot of time with her, encouraging her to sit up, trying to get her to crawl, cradling her, singing to her. Lily would miss her, Caleb realized. To be loved is to never forget.

"When you feel negativity, like if someone at your job says something to you about us, or if you're injured for a time, when you're not sure what to think or what to do? Remember you always have the answer. What is it?"

"Run it out!" Kevin called.

"Run it out. Negativity comes from Taco Bells and flight delays, and its antidote is on the trails. When you're exposed to it, don't think, seek the trails. You always have a choice, to stop or to run. Rae stopped. What do we do?"

"Run!" they each shouted, the mood shifting.

"We'll have a healing session now, a healing of the emotional pain of losing a loved one. It's what we need."

Even Aviva nodded. Mack went to his room and emerged carrying a half-full bottle of Jim Beam and a small hash pipe. June took Lily upstairs and put her into her crib. John went to the fireplace and added a large amount of cherrywood, which popped like firecrackers in the flames. Caleb felt someone staring at him. When he dared to glance up, Mack caught his eye and winked.

Then he sat down in between Alice and Makailah, and they all began to chant.

On Thanksgiving, Mack allowed a tofurkey with root vegetables.

This rare deviation from their diet was accompanied by much local ale. The day began with the annual Thanksgiving Fat Race at Bear Peak. Two hundred locals showed up for the fifty-mile run through the snowpacked course. Caleb was a monster; he won by a full minute. Every member of Happy Trails finished in the top fifty, including, to Caleb's pleasure, June. Everyone was overjoyed, and they invited the other runners over to the house to continue the party. A blowout commenced. Mack held an increasingly drunken court, opening big bottles of Beam, dispensing new ideas for the perfect head position during descents. Mostly the guests wanted to hear about the Yosemite Slam.

"The most intense ultra ever run," he beamed.

"The ultra ultra," a girl who had placed eleventh suggested.

Mack laughed loudly. "The ultra ultra. That's cool. That's cool."

Caleb approached Mack when the last guests had left. "Can we talk for a second?" he began nervously.

It was eight o'clock, and Mack was tying his laces by the front door for an alcohol-infused sprint through the snow, one of his favorite things in the world. A new dusting of icicles grew against the windowpane like DNA, spiraling, precise.

Mack looked up. His eyes were alight, the wrinkles around them like rivers flowing in reverse. He looked then as if he might accomplish anything.

"You can come with me, brother."

Outside the cold greeted them harshly. The moon was buried behind a curtain of cloud. They took off as fast as their legs would carry them into the eight inches of new powder covering the field toward the base of the mountain, sinking with every step. Mack would not slow, Caleb knew. The idea was to run until exhaustion, to fill their bodies with blood and delirium.

Suddenly Caleb's right eye began bothering him; he felt a breathtaking and pure pain. Soon he could no longer blink. As they returned, wet with sweat and leaked toxins, sober and alive, Caleb stumbled against the side of the house.

Mack leaned closer. "Hey, that f.u.c.ker's frostbitten."

He rubbed his palms together as if they were flints, breathing in deeply. He placed his palms an inch away from Caleb's face, and immediately Caleb felt a warmth caress his eye. Then it began to burn, as if a match were being held to his pupil. He pulled back.

Mack pushed his feverish hand closer to the white mucus of his eye, his face only inches from Caleb's. "So," Mack whispered, his breath full of Beam, "what do you want to talk to me about?"

Caleb stammered, "My brother wrote me."

"Yeah? What's Shane up to?"

Caleb tried to jerk away, but the back of his head pushed against the wood wall of the house. A gust of snow blew over them.

"He found medicine for Lily. If we get to San Francisco he can . . . oh," he buckled over, hands on his knees. Mack crouched down beside him, his palm still pressed to Caleb's frozen eye.

"Now, we spoke about this, Caley. I don't know how many times."

"He's got something for the baby. Can you get them to San Francisco? If I know they're there, I can . . . I can focus."

Caleb felt a crackle of fission inside his cornea, and Mack took his hand away, studied his eye. Above, Caleb saw the floating presence of a ferruginous hawk.

"Are you negotiating with me, Caley?"

"No."

"Kind of sounds like, if I say yes, you'll focus, and if I say no, you might not?"

"That's not what I mean." He felt confused. But as he blinked, his eye started to feel normal.

"Your energy is building up again. Look how fast you're healing. Most people would go to the hospital for something like that." Mack took a step back, looking into him. "You were so depleted, dude. But since I pulled you away from June and Lily, your training is astronomical. Everything I'm coaching you to do is working. After Yosemite you're going to be one of the elite athletes in our sport. And you're back obsessed with them?"

For the first time he could recall since he was a boy, Caleb felt tears running down his skin.

"Okay, Caleb. I'll bet you were a d.a.m.n good consultant. Here's a counteroffer. I think if Lily and June are off with your brother, you'll be thinking about them even more than you are now. You'll be wanting to know what's going on, wanting to call them. And you will fail at Yosemite. So my offer is this: they stay here. You keep staying away from them. Think about nothing but the Slam. Win it. After that, if Lily's not one hundred percent better, I'm not getting it done. You take them out to San Francisco and focus on them. Take as much time as you need. And then come back, open arms. Okay?"

He took a shaky, deep breath. "Okay."

"In the meantime, nothing will happen to Lily under my care. She's starting to crawl and move, which means she's building up her stores of kinetic energy. Which I can build on." Mack wiped Caleb's tears with his thumb. "However. You just had your last day working in Boulder. You're on lockdown until Yosemite. For the next six months, I don't want you distracted by anything."

Caleb nodded.

"So we don't need to discuss this again?"

"No, Mack. I get it."

"Well, then. It's a deal."

Mack went past him, inside the house. When the door opened, Caleb heard the joyful sounds of his housemates, laughing, dancing, turning up the reggae on the ancient black boom box. He stayed out in the starlit snow, his whole body shaking, a shaking that would not go away, not even after he went back inside, no matter how close to the fire he could get.

On the Monday after Thanksgiving, Prajuk committed his first crime.

Sitting in his small office, he casually slipped a thumb drive into his computer, exported the Airifan section of his gene library, and dropped the drive into his pants pocket.

All afternoon he wondered how the rest of the world could not see it there, burning through the cotton. His hand slipped down into his pocket again and again, turning it over with his fingers like a nervous groom with a ring.

At seven, his shirt damp with sweat, he drove down the highway to Greenway Plaza and pulled into a five-story-tall concrete building. He lit a Parliament and smoked it in his strange manner, holding it in his fist and sucking at the air. Then he stepped onto the elevator for the first time. On the third floor he emerged into a dim corridor and opened a door to Lab 301.

He almost ran into a heavyset cable technician walking out. Broadband had been successfully installed. He glanced around the room. It was over-air-conditioned, and the sound of the giant ducts echoed through it. He could see that equipment was trickling in sporadically, and that Shane was not quite sure what to do with it all.

The incubator had arrived first. It was refrigerator-white, square, small. Water baths, gel apparatuses, shakers came next. Ice buckets. Bunsen burners. Lab gloves.

Shane had come straight from work to find them left in a pile by the locked door to Lab 301. He stacked them against the wall of the small room.

The Promega gene kit arrived two days later. A heavy box called a centrifuge, which looked to Shane like a miniature washing machine. He opened the top and peered down at the round hole. Some miracle might take place there. He worried about contamination and quickly shut it.

Metal stools came in next. Something called a flow hood, which Shane carried to a table and out of curiosity plugged in, revealing a purple light. He lost track of time in the windowless room, s.c.r.e.w.i.n.g the wheels onto three Aeron chairs long past Nicholas's bedtime. Prajuk saw him removing a water bath from a rental box and looking around for the proper place to put it.

"Here," he offered, taking it to the long metal working counter, "like this."

Shane grinned at him. Already he had found himself growing emotionally attached to this room, its unused double sinks, its off-white walls.

Prajuk slid the thumb drive into the rented Mac and exhaled shakily as his gene library appeared on its monitor. Then he surveyed the lab, his arms crossed.

"This is how it will work."

A sense of approaching motion hung in the air.

"This thing, alpha-one ant.i.trypsin deficiency, is caused because the child was born with a gene switched off. We will isolate the protein that flips that switch on. Clone it. Grow it here. Make it therapeutic and inject it into the child. It will alter her DNA so that it instructs the gene to switch on. It's not complicated."

"Of course not."

"This thing will be taught in sixth-grade biology cla.s.s by the time your son is six."

"My sixth-grade biology teacher was a hippie slide guitarist," Shane informed him.

"They let anyone teach in American schools, don't they?" Prajuk walked around the room, examining equipment. "Proteins march through our bodies like workers going into a city, flipping switches as they go. And the body responds. Many terrible diseases are simply workers flipping the wrong switch. Did the slide guitarist explain this to you?"

"I might have been dissecting a fetal pig that day."

"Apologies. We did not have the luxury of using pigs for children's experiments in my school."

"So, how do the genes know which switches to flip?"

"The brain follows simple instructions in our DNA. You would guess this recipe for human existence is quite complicated, with millions of different steps?"

"Sure."

"But there are only four."

Shane blinked.

"T, C, A, and G are the only four nucleotides in DNA. Depending on the pattern of these four letters, you can grow a fin, glow, you can process logic, you're a cat. And so on."

Shane leaned back, listening.

"In an alpha-one ant.i.trypsin deficient patient, there is a random disruption of the pattern in the DNA. Fixing it is fairly simple. We splice out the extra nucleotide, restoring the pattern that was intended."