"I'm the chick who's about to kick the living s.h.i.t out of Jason Fischer. Where is he?" As she snarled the words, the woman brushed past Josh and began to approach Katrina.

Katrina did not back down, but rather, strode toward her confronter. "I'm sorry," she said, "but I'm not going to just offer up my postdoc to someone who wants to 'kick the living s.h.i.t' out of him. You'll have to provide a little more explanation or you'll have to leave."

"Well, that son of a b.i.t.c.h gave me herpes! How's that!"

Katrina's eyes flashed, but she continued to step forward to meet the girl. The two women stood toe to toe, almost matched in height. Their faces were inches from one another. The younger woman was slightly taller than Katrina, and Katrina's eyes were tilted upward to meet her gaze.

Katrina rose slightly onto her toes to look downward into the woman's eyes. "Look, lady," she said through her teeth, "Jason's personal life is not a drama that needs to unfold in my lab. Now, if you don't get out of here and talk to him on his own time and in his own s.p.a.ce, I'm either calling security or kicking your a.s.s myself."

After she spoke the last sentence, Katrina heard a man deliberately clearing his throat. She looked past the woman toward the sound.

Roger Gilman was standing in the doorway, leaning against the jamb. He was chuckling and shaking his head. "Oh that's lovely, Dr. Stone. Are you in the habit of threatening teenagers with violence in front of your students?"

"I'm not a f.u.c.king teenager," the woman spat. "I'm twenty-two. And who the f.u.c.k are you?"

"Special Agent Roger Gilman," Gilman answered cheerfully. He glided toward the two women and offered his hand to the stranger.

She did not take it. Instead, with a last spiteful glance in Katrina's direction, she whirled to pa.s.s Gilman and exit the room.

"Ah, Dr. Stone," Gilman said after the woman was gone, "the professionalism with which you conduct your affairs never ceases to impress me."

Gilman had to trot to catch up with the young woman in the parking lot. By the time he reached her, he was panting heavily, and he moved directly into her path as if to block her from moving forward. "Ma'am... " he said between desperate breaths, "I need to... ask you a few questions."

"What?!" The woman stepped around him.

Gilman jogged alongside her brisk walk. "We're investigating... a series of murders."

"Good for you. If I get my hands on that motherf.u.c.ker, you'll be investigating one more."

Gilman fumbled through his pockets for his notepad and pen as he ran. After locating the items, he took a deep breath and let it out quickly, then continued. "What is... your name?"

"I don't have to answer your questions." Her breathing was normal as she maintained the rapid pace through the parking lot.

"Well yes... actually... you do. As I mentioned... I'm... a federal agent investigating... a series of murders... for the government. If you don't... answer my questions... you are obstructing justice... and committing... a federal offense. So lose... the att.i.tude... answer my questions... and slow down!" Gilman stopped jogging, leaned over, and cupped his hands over his knees.

The woman reluctantly stopped walking and turned back toward him. "My name is Lisa Goldstein. What else?"

Gilman wrote the name on his notepad and continued. "What is... the nature of your... relationship with Jason Fischer?"

"There is no relationship. We had a one-night stand. I haven't seen him since. He's probably off giving herpes to some other chick dumb enough not to make him wear a rubber."

"And do you... work at this university? Are you a scientist?"

The woman ejected a sarcastic laugh. "Do I look like a f.u.c.king scientist?"

"I don't know." Gilman's breathing was returning to normal, but he was sweating profusely. He reached into his pocket for a handkerchief, which he used to mop his brow. He caught a few more breaths. "I don't really know what a scientist looks like anymore."

"Well, I'm a stripper," the woman said. "And spare me the moral judgment on that, because frankly, I'm not up for it right this minute."

Gilman was uninterested in Lisa Goldstein's choice of career. He was contemplating the notion of a Ph.D. biologist in a band who worked on anthrax and picked up strippers in his free time.

DECEMBER 2, 2015.

3:15 P.M. EST.

Roger Gilman could not stop smiling as he and Dawn strolled slowly through Lafayette Square. Directly in front of them stood a large statue of Andrew Jackson waving his hat atop a rearing horse. Centered behind the statue was the White House; behind it, the Washington monument stretched toward the heavens.

It was an unusually cold fall in D.C. A light dusting of snow already covered the square, and both Gilman and his wife wore long coats, scarves, and hats. Each of them had removed one glove, and his large hand enveloped her small one. It was just perfect.

"Mary is doing so well," Dawn was saying. "She's reading almost all by herself. When you first left town, she was crying a lot. But then she got this new determination all of a sudden." Dawn laughed at the memory. "She just comes to me and says, 'Mommy, I'm not going to cry for Daddy anymore. I'm going to learn how to read really good and then when he gets home I'll surprise him!'

"So James has been working on it with her. Every day, he comes home from kindergarten and she's waiting for him to teach her what he learned that day. It's so cute to see them camped out in their PJs, with her sounding out the words while he corrects her by sounding out the same words."

Gilman's eyes welled up. He was not ashamed. He wiped the tears softly with the gloved hand not holding Dawn's, and then stopped walking and pulled his wife into his arms. For a moment he just stood with her, not wanting to miss a moment of this time. "What about the rest of them?" His voice was on the verge of breaking.

"Oh, they're fine," Dawn said. "The older kids are a lot more used to having you gone for a while. They know you'll always be back. They're just going to school, going to church, doing their homework... sports... business as usual... you know."

Dawn fell silent as they began walking again. Wordlessly, they changed direction and began heading east, and then south along 15th street. It was as if Gilman was responding to an inexorable pull, a magnet drawing him toward FBI headquarters.

"What time is your flight in the morning?" Dawn asked.

"My driver is coming to get me at 4:50."

"Ouch!" she laughed.

"I know, but I practically had to beg just to get an overnight stay at all. This meeting is only supposed to last about an hour. Bob was going to put me back on a plane to San Diego this afternoon."

"Well I'm glad the begging worked. The kids are thrilled you'll be there when they get home from school. Speaking of which, I do have to go. Mary and James will be out soon."

For a moment, they stood at the northwest corner of Freedom Plaza, Dawn's kind eyes shining up into his. He sighed. "I need to get to work. But I'll be home as soon as I can."

"Good," she said with a hint of mischief in her voice. "I'm making pot roast." Pot roast was Gilman's favorite dinner in the winter. He smiled gratefully and hugged his wife for a long moment, his round belly pressing into her flat one.

Minutes later, Gilman was across a conference table from Teresa Wood and Director Bob Wachsman. Beside him was Sean McMullan. In front of each of them was a copy of the same status report. Bob appeared to be reading it when Gilman approached. Gilman had familiarized himself with the information on the airplane.

Teresa had written the report. "There are two primary pieces of evidence that have come to light on my end," she said after Gilman sat down. "The first is a fiber from a piece of clothing. I've had this material a.n.a.lyzed and tracked, and it helps us-well, maybe a little. It is most likely a fiber from a white lab coat. There are many other standard-issue white uniforms, all of which are generated by the same clothing manufacturer. But given all of the other evidence in this case, Ockham's razor tells me it's probably a lab coat, probably from a researcher or a doctor.

"Second piece of evidence: there was also a microscopic hair in the envelope with the card. Medium brown and fine, although the fineness of this one tiny sample doesn't necessarily mean your perp has fine hair overall. We've done a DNA a.n.a.lysis. It's from a Caucasian female."

Gilman and McMullan looked at each other. Neither spoke.

"Now, I understand we have some suspects that fit the description?" Teresa continued.

Gilman nodded grimly. "That and every other description on the planet. McMullan and I have been combing through the backgrounds of all of our San Diego-based suspects since October. Our counterparts in San Francisco are doing the same work at San Quentin. It's taking a long time. The heavy metal guitarist alone has hundreds of friends and even more enemies."

"Well," Teresa said, "get me a DNA sample from your top ten Caucasian suspects-even if they are male, because that could potentially bring a familial connection to light. Obviously, we can't rule anyone out based on the fact that their DNA is not on the card, but if we find a match then we have a pretty clear winner."

"We'll get the DNA," McMullan said. "What's your next move?"

"Well guys, I'm at a fork in the road. I have exhausted all of the a.s.says that can be done to the card using non-destructive methods. I have not found any prints, which doesn't surprise me. I'm sure your perp probably had the brain to wear gloves when handling the doc.u.ment.

"I could dust the card for prints with fluorescent powder and look using the gooseneck-that would be the most sensitive way to examine it for fingerprints. But that would contaminate the card, and if we did pick up a print, I bet it would match the hair sample so it would not give us any new information.

"So I have decided go a different route instead. I'm going to proceed with the ESDA. This will also damage the doc.u.ment, but it might pick up a trace of another writing or other indentation. So it could give us a unique piece of information. If your perp is a scientist or a doctor, as the lab coat fiber suggests, then he or she probably writes on a million things a day. We might get something from this."

"Sounds good," Bob Wachsman said. "Make it happen. What about the tracing of the postage? Linguistics? Handwriting?"

"Useless. The language is a mixture, the handwriting is a mystery, and Mason tracked the IBI of the postage stamp as far as he could, which wasn't very far. It was mailed in Phoenix. That's all we know."

"Great," said Wachsman. "So basically, our perp is anyone in Arizona."

"Or anyone in San Diego with a car," Gilman added.

"Or anyone in the world who's not afraid to fly," Teresa corrected.

DECEMBER 4, 2015.

9:04 A.M. EST.

In the main forensics laboratory at the USPIS, Teresa reached into a plastic bag with a gloved hand. She gently pulled out the White House greeting card and then took a deep breath. After a moment to ensure the entire experiment was ready to go, she laid the card, opened, onto a flat surface in front of her. Instantly, the force of a vacuum sucked the card to the surface where it formed a seal.

Teresa worked expertly and quickly. The ESDA-electrostatic detection apparatus-would pick up invisible impressions in the paper. But the longer the card sat over the vacuum, the less sensitive the a.s.say would become as the force of the vacuum increasingly flattened the impressions in the doc.u.ment. Teresa laid a thin layer of plastic film over the card and the vacuum immediately pulled the film taught. With a hand-held corona wire, she began to deposit a negative electrical charge to the entire surface of the plastic.

Then she waited. The time frame for the experiment was absolutely critical to maximize the negative charge while minimizing the damage done to the doc.u.ment by the force of the vacuum.

Teresa took pride in her skill with the ESDA. When intuition told her she was at the critical moment, she retrieved a vial of what appeared to be colored powder. In fact, the vial was filled with tiny, positively charged gla.s.s beads, coated with liquid toner. Quickly, she poured the beads over the plastic, where they automatically distributed to neutralize the charge applied to the doc.u.ment.

Gradually, a series of impressions developed as the beads were sucked into the lowest points on the doc.u.ment. The first indentations shown were those produced by the Arabic text, which became crisper before Teresa's eyes as if an invisible hand had come in with a second pen and precisely traced the writing.

A moment later, a second set of impressions began to emerge.

Teresa began to grin, and then chuckle. "d.a.m.n, I'm good," she said aloud. She reached into a drawer and grabbed a sheet of sticky, transparent film, from which she then removed the plastic backing to expose the tacky surface. Carefully, to avoid introducing air bubbles between layers, she laid the film over the newly created trace to preserve it.

DECEMBER 7, 2015.

7:45 A.M. PST.

In a San Diego hotel room, Roger Gilman sat on the bed cross-legged, surrounded by pages and pages of doc.u.mentation. On the notepad in his lap was a sketched Venn diagram. In one circle, the agent had written the names of suspects who were female and Caucasian-women whose DNA could match the hair sample Teresa had found in the greeting card. At the top of the list was Katrina Stone. Several other names were scrawled beneath that of Stone in the circle: Stone's Russian graduate student, Oxana Kosova, the heavy metal postdoc's soon-to-be ex-wife, Angela Fischer, and his crazy stripper groupie, Lisa Goldstein.

Family. Stone had both a daughter and a sister. Her mother was in the beginning of stages of Alzheimer's disease-not a likely suspect, but still ambulatory. Stone's ex-husband had remarried. Kimberly Stone. Another Caucasian female.

In a second circle of the Venn diagram, Gilman had written the names of suspects who would wear a lab coat or other white standard-issue uniform. Katrina's ex-husband, Tom Stone, had been included. He was a medic. Stone's other female student, Li Fung, was not Caucasian but she did fit into the second circle. So did the rest of Stone's staff.

Asked to provide DNA, Li had willingly submitted as had Joshua Attle. Jason Fischer had said, "f.u.c.k you-come back with a court order," without looking up from his experiment. Todd Ruddock had provided the sample along with a middle finger, and then cheerfully requested with his charming British accent, "Now b.u.g.g.e.r off, will ya?" Angela Fischer had agreed to provide a sample and then slapped Gilman across the face when he plucked the hair from her head.

Gilman had not managed to locate Lisa Goldstein. According to another stripper at the club where she worked, Lisa had a tendency to go on "vacation" with some of her "clients" and would probably be back at some point.

The area of overlap between the two circles contained only two names-only two Caucasian females who would wear lab coats. Oxana Kosova and Katrina Stone.

A third, non-overlapping circle was reserved for suspects who had no obvious ties to either the hair sample or the fiber. The ISIL network, which had been silent on the matter since day one of the investigation. Other international terrorist organizations. Domestic terrorists. Also in the third circle was the phrase "2000 Hispanic Prisoners," and beneath that, "Prisoners' Victims."

Lawrence Naden was, indeed, sitting in a prison cell in Texas. Not a suspect. Gilman had written his name outside of all circles and then drawn a direct line to the name of Katrina Stone. One woman in the center of the diagram. One woman at the center of it all.

Gilman reflected back on his short, wonderful visit to Washington, D.C. and sighed.

His cell phone began to ring. Gilman crawled over the paperwork on his hotel room bed and began rifling through clothing on the floor. Finally finding his phone in the pocket of a pair of slacks, he clicked into the call. "h.e.l.lo, this is Roger Gilman."

"Hi Roger, Teresa Wood calling from Dulles. I've got good news and bad news. Do you have a few minutes?"

Gilman scrambled to find a notepad and pen. "Uh, sure. Hang on a minute."

The hotel staff had been given strict instructions to leave the room alone and had evidently been complying. Gilman found what he was looking for and shoved a few papers on the bed aside before sitting down. He uncapped his pen. "What did you find with the DNA?"