Gavin stepped into the vacated space and extended a hand the size of a ham. The blunt fingers were manicured. "Maurice Gavin. This way, please." Gavin strode past the desk. I scurried to keep up.

A minute later, we were comfortably ensconced in a burgundy office the size of a tennis court. The left wall was all window, offering a breathtaking view of the Manhattan Bridge and the East River. The burnished surface of Gavin's desk was empty except for an inset keypad and a rack of data pebbles. The wall behind was covered with photos: Gavin in a hardhat, Gavin with presidents, Gavin winning awards, Gavin anchoring a relay team, Gavin peering into a microscope. The self-proclaimed Renaissance man.

He motioned for me to sit. He himself sank into something befitting an emperor and folded his hands across his chest. He stared at me, waiting for me to start. Do not waste my time, the placid gaze said.

"Thanks for seeing me," I said.

"Morris Crandall is a good friend, and an important employee." He opened his palms. "Anything I can do." He had the eyes of a hawk, dark and glassy.

"Ms. Struldbrug said he was working on a project related to the Shift," I started.

A nod. "Analyzing reborn and normal DNA."

"So you believe the cause of the Shift is genetic? I'm hearing a lot of talk about how time has reversed itself. The Enders think this is Armageddon."

Gavin repressed a pained look. "I know the world prefers to believe in fairy tales, to buy clocks that run backwards and dress in antique clothing. But when we finally unravel this, it will turn out to be perfectly rational, and perfectly scientific."

"Okay. So what has happened?"

Gavin drummed his fingers on the table. "We don't have all the components, of course..."

"So give me what you do have."

"It's quite technical. And I'm not sure it's germane." His smile was laced with contempt. This guy had you instantly pegged, based on your alma mater and the height of your IQ. Which put me around the level of an amoeba.

"Why don't you let me decide what's germane? Unless you have some reason to distrust me. Perhaps you'd like to speak to one of my friends on the force to establish my credentials?"

Gavin looked like I was an impertinent fly he wanted to swat. "You have no friends on the force, Mr. Donner. Except perhaps your old partner. And he is terrified of you. Or hadn't you noticed?"

He'd taken my bait and revealed that someone-Nicole, her brother Adam, or Gavin himself-had had me investigated. These people either had a lot to protect or a lot to hide-or both. I looked at Gavin hard enough for his smugness to falter. "I guess my report to Ms. Struldbrug will be that you were uncooperative."

He shifted hotly in his throne. "It appears I'm going to give a science lesson this morning."

"I was good in science."

"Obviously," sighed Gavin, "the Shift is tied to the biology of aging."

I shrugged. "Obviously."

"For centuries, scientists have been trying to fashion theories of aging that explained the process. In the 19th century, it was the 'things fall apart' theory."

"We're just machines. Which eventually break down."

"Very good. The 20th century brought new theories of aging. The biological clock theory, which asserts that the body has a built-in, pre-set lifespan limit. Then, for a while, it was popular to view aging as a disease, something that could eventually be cured. As most solutions are, it was too simplistic. Some aging processes do resemble that of a disease, but we think the body also has built-in regulators that enforce a lifespan limit."

"Which is?"

"The maximum lifespan for homo sapiens, we think, is around 122 years, give or take."

"So the 'things fall apart' theory is wrong, then?"

Gavin shook his head. "None of them are wrong, per se, just incomplete. The body does fall apart. Not surprising, considering it's under constant attack."

"Attack?"

"You've heard of free radicals?"

"Yeah. They're bad."

"Most people don't realize the delicious irony that oxygen, the thing that sustains us, is also slowly killing us."

"Huh?"

"The most dangerous free radicals are oxygen-centered."

"So while oxygen keeps our lungs pumping, it's also slowly killing us?"

He nodded. "Oxidized free radicals burn through delicate cell membranes, injuring proteins, lipids... even our DNA."

"Well, shit. What's the point of quitting smoking?"

"Oh no, the amount of radicals in cigarette smoke..." He realized I was joking and screwed his mouth sideways. "Antioxidants are naturally-occurring enzymes which minimize free radical damage. Think of them as the body's toxic waste cleanup crew. Even so, the body still experiences a staggering amount of oxidant hits a day. Add it to other chemical damages, and each genome in each of your cells endures 30,000 damage events every day."

"Each genome?"

"Right. So, if the average adult human body contains about 10 trillion cells, on a typical day your DNA could rack up about 300,000 trillion hits."

I whistled. "But not everybody wears out at the same rate, does it?"

"No. Our genes also determine how quickly, and how well, we age."

"I see what you mean about it being complicated."

"Oh, we're not nearly done."

I was afraid of that.

"We haven't taken into account the cumulative mistakes theory. When cells reproduce, divide, and replace themselves, it's called cell doublings. Cell doublings are directly related to the longevity of the species. Look at this chart."

He hit a button on his desk and scrolled through some holoimages. He finally punched up a little graph: SPECIESLIFESPANCELL DIVISION CEILING.

Mice3 years15 divisions Chickens12 years25 divisions Humans122 years50 divisions Galapagos tortoise175 years110 divisions "Gotta get me some turtle DNA." Gavin didn't laugh. "So cells only have so many divisions in them?"

"It's called the Hayflick limit. On top of that, cell division involves literally hundreds of factors and changes... a lot that can go wrong. And does, incrementally. Eventually cells start dying, making mistakes, even on the genetic level. Since these accumulated mistakes make the body more vulnerable to age-related diseases, one almost always dies well before their cell division limit is reached."

"So... we wear out, and we have built-in cell limits, and a biological clock that's running down. Sounds like the deck's stacked against us."

"More than you know. Now, as to telomeres-"

"Christ. There's more."

"Oh yes. We spoke about the genetic component. Each chromosome ends in a series of protective units called a telomere. Think of them like the plastic tips at the end of shoe laces. These telomeres don't contain genetic information, just an empty number of repeating subunits, which shorten after each division."

"Each time the DNA reproduces, it's one unit shorter?"

"These units may serve as counting markers, growing shorter in direct proportion to how near the cell comes to death. Contrarily, cancer cells replenish their telomeres after each division. That's why cancer grows so wildly out of control."

I shook my head. "So for a person to be immortal, he'd have to have," I ticked off each item on a finger, "cells that never made mistakes, cells that reproduced infinitely, a body that repaired itself perfectly from free radicals and other assaults, a biological clock that never ran down, and telomeres that didn't shorten."

"And a host of other factors we haven't even discussed."

"And we haven't even gotten around to the issue of actually growing younger."

Gavin leaned back in satisfaction. "I think you can see why, even after twenty-five years of research, a cure for the Shift is still a long way off."

"Okay, so let's get back to Crandall. His team was working on all this stuff."

Gavin, who'd been swept away by his own breathtaking command of science, tightened suddenly. "That's right. Our best and brightest. Morris Crandall, Dr. Smythe, Dr. Hakuri, and Dr. Renquist."

"What aspect were they working on, specifically?"

Gavin hesitated. "They believed, since the issues involved in youthing are genetic, gene therapy could stop the Shift."

"Gene therapy? How does that work?"

"In a nutshell, you modify the part of the DNA that is causing the problem. You place the modified genes into a harmless vector-a retrovirus-and introduce it into the patient."

"Sounds like science fiction."

"We've managed to cure some nasty inherited diseases that way. We believe a retrovirus is what communicates the Shift in the first place-what begins the alterations in 'dead' DNA that causes revival."

"Really?"

"Many cancers are caused that way. HIV, before it was cured, was carried by a retrovirus called a lentivirus. Morris believed we could restore normal functioning of the biological processes in reborns using gene therapy."

"Get the clock to run forward again."

"That's right."

"What about communicability? I was told that even norms can cause the Shift to start outside the Blister."

"Because we don't have a vaccine for the Shift retrovirus yet, our only option is to contain it. Every infected person, norm and reborn alike, must be isolated."

"But these retroviruses are just carriers, right? So what caused the Shift in the first place? Where'd it come from?"

"That's the million dollar question, isn't it? The most accepted theory is that some bioweapon didn't perform as advertised, either through a spontaneous mutation, which happens in nature, or because the terrorist genetic designers didn't know what they were doing."

"A bioweapon? You mean like weaponized anthrax?"

"Well, yes, but bioterrorism has become much more sophisticated."

"How many nations or terrorist groups can modify DNA?"

"You'd have to ask the Conch. But zealotry, money and technology is a pretty potent combination, and there's no shortage of America-haters."

"No terrorist group or state was ever identified. No one ever claimed responsibility."

"No one credible, no."

"The worst attack on American soil in history, and the attacker was never identified. Hard to believe."

He merely shrugged.

"Crandall spoke to Nicole of a breakthrough in their research."

Gavin raised an eyebrow. "Team records show nothing."

"Are you saying she lied?"

His oily smile became slush. "Of course not. I have no idea why Crandall told her that."

"Could Dr. Smythe's death be connected to Crandall's disappearance? To their work? A rival drug company, maybe?"

Gavin dismissed the idea with a wave. "Big pharmaceuticals conduct industrial espionage every day, but murder? Doubtful."

"Could this killer be some crazy Ender who's a fan of the Shift?"

"Our work is classified. Besides, I understood that Dr. Smythe's death was related to his rather unusual personal tastes."

Everyone seemed anxious for me to buy the party line. "It's possible. Was Crandall acting strangely in any way prior to his disappearance?"

"No, his staff said it was business as usual."

"Which involved late nights?" Another nod. "Where is his lab?"

"We have labs all over town. Smythe's was in Hippieville."

I raised an eyebrow. Gavin suppressed his amusement. "I forgot you haven't ventured much out of the Bogart yet."

"The Bo- Oh, you mean midtown! Where everyone looks like they stepped out of The Maltese Falcon?"

Gavin nodded. "In the Village, many people have, unsurprisingly, adopted the sixties as their retro style. Incense, meditation and peace signs."

"Groovy."

"Dr. Crandall worked at a lab in Chelsea."

"Who typically would be in this building after closing?"