Then she blinked and looked up. "Do you have a mug shot of the San Quentin inmate?" Gilman reached into his briefcase and removed an eight-by-ten black-and-white photograph. He handed it to Katrina. "Yep, that's him all right," she said, exasperated.

For a brief instant, she struggled with the question of how the man could have been in two places at once, and then suddenly, understanding dawned. Katrina looked again at the photograph and her eyes narrowed, but then, she was smiling.

The scar. The scar over the man's eye in the photograph. It was subtle. But it had not been there in the laboratory.

Quietly, Katrina began to chuckle to herself. The two other investigators exchanged a confused glance, and then they, too, began to laugh.

"How could we have missed it?" Gilman asked.

"Because we weren't looking for it," McMullan answered. "In fact, I bet they've been masquerading as one man for a long time."

FEBRUARY 4, 2016.

4:01 A.M. PST.

In his shared minimum-security cell at San Quentin, Oscar Morales lay awake in a rare state of insomnia.

Two hours earlier, it had been a dream that awakened him. In his dream, Chuck had been at the prison. Oscar had handed his brother two vials of anthrax across the table of the visitation room. And with a smile, Chuck had opened one of the vials and swallowed its contents like a shot of whiskey. Oscar had been powerless to stop him.

Chuck's grin quickly decayed from sweet into freakish as an eruption of black sores obscured the flesh of his face. As Oscar watched, helpless, the sores grew together and began bursting, leaving behind a blackened, b.l.o.o.d.y nightmare of devoured flesh. Chuck raised his hands-also corroding-to his face and began to scream.

But the scream that awoke Oscar was his own.

"Shut the f.u.c.k up!" his cellmate shouted, and Oscar snapped out of the dream.

Still sitting beside the hospital bed, Katrina looked down at the thick file in her hands. McMullan and Gilman had left the room to retrieve the personal belongings of the man in the bed, the identical twin brother of a San Quentin inmate named Oscar Morales.

Katrina was examining Roger Gilman's Venn diagram of suspects in Operation Death Row. She was at the center. She could understand why. The data before her was circ.u.mstantial, but it pointed repeatedly to her. Her preliminary inhibitor data from the original grant application. A witness' claim that a female had ransacked Jason's apartment. A lab coat fiber located in the greeting card. The card itself, bearing the same crystal structure she had posted on her office wall.

Katrina flipped through the pages of the file and saw a photocopy of the White House greeting card. For a moment, she studied the crystal structure of the anthrax toxins interacting with the host cell. There were no alterations to the structure; it was indeed identical to the image printed in the 2004 issue of Nature.

She opened the card and stared at the Arabic text, and then found the English translation on a subsequent page in the file.

Dear Mr. President, Your nation of puppets will soon know at last the price of fighting against our Islamic State. Those of you who survive Allah's justice will reflect upon 11 September of 2001 and consider that date insignificant.

A small taste of the pain we promise has already been put to course. Make no mistake that the blood that will flow is on your hands. Let it paint for you an image of our strength and resolve. Let it serve as a reminder that you cannot defeat Islam.

You will stand powerless and witness this small shedding of blood, and you will then have the privilege of living in fear for two months, as our faithful brothers and sisters have lived in fear of your Christian Crusaders.

And finally, on your Christmas Day of this year, there will begin a cleansing of your country unlike any you can possibly imagine. It will blanket your nation and no man, woman, or child will be safe. Only Allah will decide who may be spared.

Our Muslim brothers and sisters have been imprisoned by the western leaders for too long. The world will now see that you are the prisoners, and Allah will praise the final victory of ISIL.

Katrina reviewed the text several times. A small taste of the pain we promise has already been put to course. Imprisoned. Prisoners. It will blanket your nation. Christmas Day. This year. ISIL. But Christmas had come and gone, and there had been nothing. Why? Katrina began committing the text to memory.

Her concentration was broken when the door opened and Gilman and McMullan re-entered the hospital room. Both looked pale. In McMullan's hand was a ziplock bag, which he held out to her with trembling fingers. "We've been through this man's personal effects," he said. "These were in his pocket."

Katrina took the bag from Sean McMullan and gripped one of the two sealed gla.s.s vials through the plastic. In contrast to those of the FBI agent, her hands were steady as she shook the vial gently to observe the movement of the powder inside. "You haven't opened this, have you?" she asked calmly.

"Oh, h.e.l.l no!" McMullan said.

"Good. What about the hospital staff?"

"We asked," Gilman said. "They say they haven't either."

"I bet you a million to one I know the exact molecular composition of what's in these vials," Katrina said. "Leave the a.n.a.lysis to me and I'll confirm it. It can be done with PCR by late morning."

"Absolutely not," Gilman said. "We've already gone out on a limb by not giving you the file that you're not looking at right now. There's no way we're letting you take over the forensic a.n.a.lysis of this investigation."

"I have no interest in taking over the forensic a.n.a.lysis of the investigation, but I can have this done before the San Diego FBI wakes up for the day. This is what I do, all the time."

"Forget it, Katrina-" Gilman began to say, but she cut him off.

"Seriously, Roger! What are you afraid of? That I'll use the anthrax to poison someone? Do you not realize I could have done that at any time over the last several years? Do you not realize that even if you take these vials with you, I can go to my lab right now and take out another?"

"Oh, for Pete's sake," Gilman said finally. As he said it, he looked at his watch. It was now 4:33 a.m. and the three of them had been at the hospital since Katrina's attacker had been admitted the previous evening. "I have to go get some sleep. If you can really finish that a.n.a.lysis by tomorrow morning-or this morning, I guess it really is-be my guest. But I want the other vial for our forensics team to confirm whatever you find."

"Of course," Katrina agreed.

Gilman looked to McMullan, who nodded approval. "I'm going to sleep too, Katrina," McMullan said. "You OK?"

"Yeah, I'm fine," she said, but there were heavy bags under her eyes. "I'll harvest the DNA in BSL-3 and then the rest can be done in BSL-2. All I have to do is set up the PCR, take a nap while the machine runs, and then run the gel. It will only take about twenty minutes after that. I'll have the data by the time you guys wake up. Then it's my turn to sleep."

Katrina pulled one of the vials from the ziplock bag, resealed the bag and returned it to Sean McMullan. With a final nod, the two FBI agents left the hospital room. Katrina gathered her belongings and the FBI file and left for the BSL-3 facility.

5:23 A.M. PST.

As soon as Roger Gilman arrived back at the hotel room that had now been his home for several months, his cell phone chimed. Exhausted, he picked up the phone and looked at the caller ID. Dawn had called seven times.

Gilman's state of sleep deprivation began to feel like a break with reality as he listened to the multiple voice mail messages from his wife. In the first, a hint of concern was reflected in Dawn's voice. Subsequently: conviction, trepidation, and anger. With each reading of the card, Dawn had become increasingly aware of its implications. The card was a threat. Mailed to their home. Where seven children were sleeping.

"... creepy greeting card... funny looking flowers... how unfortunate... speak my language... The Doctor... "

Creepy greeting card. Funny looking flowers. Gilman sat down, hard, on the bed, and began to breathe deeply. For a moment, he thought he might faint. Then he called his home in Washington, D.C.

Dawn answered on the first ring.

"Where is the card now?" he asked immediately.

"In a ziplock bag, sitting on the kitchen table in front of me."

"Describe the 'funny flowers' to me," he said, and she did.

"Dawn, leave the card right where it is. Gather up the kids and get them out of the house. Take enough stuff for a few days and go to your mother's. There might be no real cause for concern, but I'm not taking any chances. There will be FBI investigators at the house within the hour to remove the card. Don't touch it again."

Dawn began to weep softly, and Gilman sat quietly on the phone to allow it to pa.s.s. After a brief breakdown, Dawn cleared her throat. "OK then," she said. "I know you can't tell me what's going on, but I trust you. I'll do as you say. But Roger, please come home when you can. I need you."

"I'm already on my way."

It took four phone calls for Gilman to secure a flight from San Diego to Washington, D.C. He made the calls in the car on the way to the airport. Once the flight was scheduled, he made two additional calls.

The first was to Guofu Wong, the CDC epidemiologist heading Operation Death Row. Wong a.s.sured Gilman that there would be special agents and a HazMat team at the Gilman house in twenty minutes. And that, as soon as he could, he would personally join them from Atlanta.

The second call was to Sean McMullan's cell phone.

"h.e.l.lo?" McMullan said groggily.

"McMullan, wake up!" Gilman practically shouted.

"Oh, G.o.d, now what?"

"Who gets your mail when you're out of town?"

"Come again?"

"Where is your mail for today?"

"My personal mail?"

"Yes!"

"It's being forwarded to me here in San Diego. It, ah, comes to a P.O. box. I pick it up every three or four days."

"When was the last time you picked it up?"

"A couple days ago. Roger, what are you talking about?"

"I got a greeting card. At home. My wife opened it. It's got a bouquet on it and a weird message. From Dawn's description, the bouquet sounds like the same one from the other card. The bouquet that's really the molecular structure of anthrax."

Sean McMullan paused. "You mean the writing was in English?" he asked, bewildered.

"Well my wife doesn't speak Arabic, as far as I know."

"Why do you think I'd have something in my mail just because you did?" McMullan asked.

"Because whoever wrote that card knows I'm the investigator on this case. And you're the other one. So if you don't have something similar in your mailbox, then I'm obviously being personally targeted. And our number one suspect clearly likes you a h.e.l.l of a lot more than she likes me." And with that, Gilman hung up.

7:09 A.M. PST.

Katrina purified the DNA out of the anthrax in the vial at her BSL-3 facility in Sorrento Valley. Once the infectious material from the bacteria was removed, the DNA itself was harmless. So she returned to her lab at SDSU, which was en route to her house and the bed she so longed for.

For the first time in months, there was no guard at the laboratory door. The guard that should have been on duty was currently at the morgue. A chalk outline had been traced where he had fallen, and the door was locked and blockaded off with police tape. Katrina yanked it aside and stepped into her lab, her shoes sticking in the blood that had now become tacky.

Katrina took the reagents she needed from a freezer and rubbed the vials between her fingers to thaw them. It only took a few minutes to set up the PCR reaction.

One of the most widely used techniques in modern molecular biology, PCR is nothing more than a succession of repeated cycles of precisely controlled temperature fluctuations. Once, researchers were required to submerge the reaction by hand, one step at a time, into a series of water baths to alter the temperature manually. Today, the process is automated. The scientist merely places a reaction tube into a machine and dictates the temperature changes and timing on the machine's computer. And then waits.

Once Katrina had programmed the PCR machine, she had a two hour and forty minute wait for the reaction to reach completion before she could look at the results on a DNA gel. She pressed the start b.u.t.ton and sat down at the lab bench beside the machine, finally succ.u.mbing to her exhaustion.

As she began to fall asleep, Katrina tipped sideways off of the chair she was sitting on and then quickly jerked awake. Her mind dazed, she glanced up and saw a puddle of clear liquid on the floor between the main lab and the robot room. She recognized the liquid as the portion of hydrochloric acid that had missed her attacker's face. The puddle reminded Katrina of a series of events that couldn't possibly have taken place in this room just the evening before. The prospect of sleep was suddenly over.

She stood up and began wandering through the lab, retracing her steps and those of her attacker, whose first name she still did not know. Morales. Something Morales. Twin brother to Oscar Morales. The Oscar Morales at San Quentin.

Except for the mess at the front door, and a few smears of Something Morales' blood and facial tissues on the floor where he had fallen, the lab looked remarkably innocuous. Like the other robots, Octopus was still working away as if totally disinterested in murders, murderers, or Katrina's self-defense tactics with his jerky robot movements and concentrated hydrochloric acids.

As Katrina walked past the robot room and into the room beyond, her eyes fell upon the liquid nitrogen tank, and something dawned. The activator data was still in there. She and Jason had hidden the data months ago, and she had never had a chance to dig it back out. The lab had always been guarded. Until today.

Katrina shook her head rapidly from side to side for a moment in an attempt to clear the fogginess of sleep deprivation. She needed the capacity to think.

There had now been a murder in the lab. If the activator data had been a threat before, it was an even bigger threat now. Perhaps it was time to destroy it for good. And this might be her only window, her only chance with no guard at the lab. And besides, she no longer needed it.

Katrina glanced around momentarily, as if she might see someone else in the room. Of course, she did not.

She found the stool used to reach the top of the tank and the blue cryo-gloves required to touch its contents. Then she reached into a closet to retrieve the item she had purchased from the humane society where Alexis worked.

Over the course of the last few months, Katrina's lab had become the most sophisticated infectious disease laboratory in the world. Within it, the shiny new p.o.o.per Scooper looked ridiculous. But with its stainless steel arms, long reach, and plastic handles, it was the perfect tool for retrieving something from the bottom of a tank held at one hundred ninety-six degrees below zero.

Katrina raised the lid of the tank and stood back to allow the initial cloud of sublimation to puff out. Then she waved away as much of the residual vapor as possible with a blue glove. She removed the four towers that she and Jason had placed atop the cryogenic bag containing the data and set them onto the floor. Then she fished out the bag with the p.o.o.per Scooper and dropped it onto the linoleum.

After replacing the towers and closing the lid, Katrina used a gloved hand to pick up the still frozen bag. And as she did, she heard a door close.