Genevieve greeted Brisling under the shade of CDC Building 18. It was all cold steel and green glass. She wore another of her flowery dresses, shorter and trimmer than before, her smooth, graceful arms bare from the shoulders down.

"What's wrong?" she said. "You look like hell."

Brisling stretched his lower back, wincing. "I spent the night there."

"Hotel bed?"

"No." The bed was fine. It was the thought of that poor girl that kept him awake all night. It reminded Brisling of his internship back at Massachusetts General, jolting awake every ten minutes to the beep of his pager, convinced he had prescribed the wrong dose of the wrong medicine to the wrong patient. Now, all these years later, he had actually done it. At least it felt that way, despite what the police were saying about Anna Jankowsky's death.

He stood straight and appraised the woman before him. "I don't know how you manage to look so lovely all the time."

She crossed her arms and frowned. "Was it that call from the Seattle Police? What did they want?"

"I don't want to talk about it."

With a curt nod, she handed him a temporary ID badge and led him inside. They passed the security checkpoint and stepped into an elevator. Brisling stared up at the cold blue LED display. "I don't recognize a damn thing here."

"There isn't much of the original campus left."

"My old lab space?"

"They tore it down. It's a daycare center now."

A daycare center. The thought of it pulled him back. He had wanted Judith to stay home with the baby. She had wanted to go back to school. They were arguing about it on their way home from Ansley Park the night of the accident.

With a chime, the elevator doors opened, and Genevieve stepped out into a bright hallway, beckoning Brisling to follow.

Brisling hesitated. For a moment, he imagined the doors slamming shut, the elevator falling, plummeting to the bottom of the sea. That was where Genevieve had found him that night, three months after the funeral, slumped behind his desk with a bottle of bourbon, murmuring to a little audience of sleeping pills. She hauled him up, but she did not drag him ashore. Instead, she offered him a terrible choice: sink or swim. And he swam to her. Together, they flushed the sleeping pills down the toilet, but the bourbon they shared, blending it with her sweet iced tea until the liquor was gone and they had cried themselves dry.

In the months that followed, Brisling poured himself back into his research. He published at a feverish pace. He won enormous grants. He hired so many technicians and post-docs that he scarcely knew their names. He lectured far and wide—anything to keep him from the home and the bed he had shared with Judith.

Now, Brisling stepped out of the elevator, and Genevieve led him down a bright, airy corridor.

"Do you have the demographic data I asked for?" he said.

She stopped in the middle of the hallway and handed Brisling a sheet of paper. On it was printed a color pie chart showing the racial and ethnic breakdown of all recent PML cases being tracked by the CDC.

Brisling studied it. "There's something off here."

"You're right. Look at the green wedge, the one for Hispanics."

"It's just a tiny sliver." They stepped aside to make way for a janitor and his cart.

"There's something else."

"I don't see it."

"That's because you can't see what's not there."

In his mind, he checked off all the racial and ethnic categories recognized by the US government. "What about our redskin friends?"

"Royal!"

"What?"

"That's a hateful slur. I won't tolerate that kind of behavior, especially if we're going to work together."

He held up his free hand. "Sorry. Let me rephrase that. No cases in American Indians or Alaska Natives."

If Genevieve was satisfied, she did not show it.

"I said I was sorry."

She sighed wearily. "We'll talk about this later."

"Fine." He wagged the paper in his hand. "But couldn't this just be sampling error? American Indians are only about one or two percent of the US population, right?"

"Right, but it's both Hispanics and American Indians who are unrepresented here. I don't think that's a coincidence. There's a connection."

"Go on."

"A lot of folks in the US identifying as Hispanic have indigenous ancestry, mostly from Mexico and Central America . . ."

The implications bounced around Brisling's mind, joining up, breaking apart, recombining into new possibilities, strange and frightening.

". . . Genetically, they're descendants of the ancient Aztecs and Mayans."

Then it popped out of his mouth like a gumball. "Genotype."

"Excuse me?"

"You're right, it is genetics. But not human genetics. It's viral genetics, JCV genetics."

"I'm afraid you've lost me."

"Listen. The JC virus is evolutionarily ancient. Our human ancestors carried it out of Africa. And as human populations changed and adapted to their new environments, so did the virus. Today, each major racial group on earth carries its own unique JCV strain, or genotype. Genotype 3 is found in Sub-Saharan Africa, genotype 1 in Europe, genotype 7 in Southeast Asia, et cetera."

"Are you saying American Indians have their own genotype?"

"Yes, genotype 2. Actually, it's carried by indigenous people all through the Americas, from Canada and Alaska down to Chile."

Her eyes narrowed. "So JCV genotype 2 is somehow resistant to reactivation?"

"Maybe, but that wouldn't explain why every other genotype is reactivating, would it?"

She took him by the arm. "Come now, let me show you what I told you about last night."

The lab was spacious, clean, and modern. Floor-to-ceiling windows looked out over the variegated forest north of campus. The only thing Brisling recognized was the bready smell of bacterial growth agar brewing on a hotplate somewhere. At this early hour, most of the lab technicians were still in bed, but in the far corner, a Black girl in a white lab coat hunched over something on the bench. As they approached, Brisling could see it was a small polystyrene assay plate.

Genevieve laid her slender fingers on the girl's shoulder. "Good Morning, Lisa. I'd like you to meet Dr. R. K. Brisling, the one I told you about. He worked here during the early HIV days."

Deftly covering the plate with a transparent plastic adhesive strip, Lisa removed her gloves, stood, and shook Brisling's hand. She had a sad, boyish face and pale brown eyes. Her big blond Afro wobbled as she spoke. "It's a pleasure to meet you, sir. It's not often we get to put a face on the history of this place."

Genevieve offered Brisling an apologetic shrug then said to Lisa, "Why don't you show Dr. Brisling what you found last night."

"Sure. So, we've gotten about five hundred spinal fluid samples from PML cases all over the US. I've tested about three hundred so far and confirmed JC virus DNA in every single one of them."

"Good," said Brisling. "Which technique did you use?"

"PCR. That stands for polymerase chain reaction."

Brisling took a deep breath and counted silently to three. "I meant, what type of PCR, quantitative or semi-quantitative?"

"Oh, semiquant."

"So you're saying you couldn't be bothered to do full quantitative PCR."

"Royal!" said Genevieve, hands on her narrow hips. "I won't tolerate that, either."

Lisa held up her hand and said to Brisling. "No. You're not wrong. Normally I'd run quantitative PCR, but we needed a quick answer, so I just did semiquant. If I hadn't, I would have missed it." Lisa called up an image on her computer screen. "This is one of the gels I ran to resolve the PCR products."

Brisling leaned over for a closer look, glasses sliding down his nose. The gel itself looked like a shadowy rectangle set against the black background. About a third of the way down, a string of glowing orange dashes—or bands, as they were called—stretched from side to side. Each band, he knew, represented JCV DNA that had been amplified from a patient's cerebrospinal fluid.

"They're running right where we expect them, two hundred and fifty base pairs. But look close," said Lisa.

Brisling repositioned his glasses and leaned even closer. Just below each band was a second band, only much fainter. He jabbed his finger at the screen. "What are those?"

"I know, right?" said Lisa, staring at the screen. "There should only be one PCR product per patient, not two."

"That's what we wanted you to see," said Genevieve. "What do you think?"

"I think you have a quality-control problem here. Something's wrong with your PCR primers. Did you run the proper controls?"

"Of course," said Lisa.

"Show me."

Lisa called up a second image, similar to the first. "I ran this gel at the same time. These are from PML samples the CDC archived during the AIDS epidemic, back in the eighties. See, there's only one PCR product, right at two-fifty base pairs. So my primers are working perfectly." She clicked back to the original image with its double bands. "What I'm wondering is if this extra band is a mutant form of JCV."

"Is it present in every sample?" said Brisling.

"All three hundred I've run so far, but none of the historical controls."

"Then it's definitely not a mutation."

"Why not?" said Genevieve.

"Because that would mean the same mutation arose in multiple populations at the same time. That's just not possible."

"Well then what is it?"

"A second virus, close enough to JCV to be picked up by the primers, but different." He paused. "Yes. It might be a helper virus that's activating JCV in people's brains."

"Good Lord," said Genevieve.

Brisling turned to Lisa. "Can you sequence that second band?"

She nodded, her Afro bouncing again. "We can do more than that."

"What do you mean?"

"We can sequence every bit of DNA in these samples. If there's a second virus there, we'll find it."

Brisling turned to Genevieve for confirmation.

"We do have a high throughput sequencing core across the street. I'll bring all resources to bear on this if you want."

"What about De Soto?"

"He doesn't have to know. Not yet."

"Then let's do it," said Brisling. "Lisa, if you find something—anything—I want you to design new PCR primers that will detect only the new virus and not regular JCV. Then overnight them to my lab in Seattle."

"Why?" said Genevieve.

"I'm going to have a lot of samples to analyze when I get back."

"What samples?" she said.

"The ones you and I are about to round up." Senator Flaherty had called it right. Hindsight is twenty-twenty, but foresight is one in a million.

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