The FBI National Academy in Quantico, Virginia, is a brick and glass oasis in the midst of an artificial war. I would never forget my first stay there years ago. I went to bed and got up to the sound of semiautomatics going off, and when I took a wrong turn on the wooded fitness course one afternoon, I was almost flattened by a tank.

It was Friday morning. Benton Wesley had scheduled a meeting, and Marino perked up visibly as the Academy's fountain and flags came into view. I had to take two steps for his every one as I followed him inside the spacious sunny lobby of a new building that looked enough like a fine hotel to have earned the nickname Quantico Hilton. Checking his handgun at the front desk, Marino signed us in, and we clipped on visitor's passes while a receptionist buzzed Wesley to affirm our privileged clearance.

A maze of glass hyphens connect sections of offices, classrooms, and laboratories, and one can go from building to building without ever stepping outside. No matter how often I came here, I always got lost. Marino seemed to know where he was going, so I dutifully stayed on his heels and watched the parade of color-coded students pass. Red shirts and khaki trousers were police officers. Gray shirts with black fatigues tucked into spit-polished boots were new DBA agents, with the veterans dressed ominously in solid black. New FBI agents wore blue and khaki, while members of the elitist Hostage Teams wore solid white. Men and women were impeccably groomed and remarkably fit. They carried with them a mien of militaristic reserve as tangible as the odor of the gun-cleaning solvent they left in their wake.

We boarded a service elevator and Marino punched the button designated LL (for Low Low, so the joke goes). Hoover's secret bomb shelter is sixty feet under ground, two stories below the indoor firing range. It has always seemed appropriate to me that the Academy decided to locate its Behavioral Science Unit closer to hell than heaven. Titles change. The last I heard, the Bureau was calling profilers Criminal Investigative Agents, or CIAs (an acronym destined for confusion). The work doesn't change. There will always be psychopaths, sociopaths, lust murderers - whatever one chooses to call evil people who find pleasure in causing unthinkable pain.

We got off the elevator and followed a drab hallway to a drab outer office. Wesley emerged and showed us into a small conference room, where Roy Hanowell was sitting at a long polished table. The fibers expert never seemed to remember me on sight from one meeting to the next. I always made a point of introducing myself when he offered his hand.

"Of course, of course, Dr. Scarpetta. How are you?" he inquired, just as he always did.

Wesley shut the door and Marino looked around, scowling when he couldn't find an ashtray. An empty Diet Coke can in a trash basket would have to do. I resisted the impulse to dig out my own pack. The Academy was about as smokeless as an intensive care unit.

Wesley's white shirt was wrinkled in back, his eyes tired and preoccupied as he began perusing paperwork inside a folder. He immediately got down to business.

"Anything new on Sterling Harper?" he asked.

I had reviewed her histology slides yesterday and wasn't unduly surprised by what I had found. Nor was I any closer to understanding her cause of sudden death.

"She had chronic myelocytic leukemia," I replied.

Wesley glanced up. "Cause of death?"

"No. In fact, I can't even be sure she knew she had it," I said.

"That's interesting," Hanowell commented. "You can have leukemia and not know it?"

"The onset of chronic leukemia is insidious," I explained. "Her symptoms could have been as mild as night sweats, fatigue, weight loss. On the other hand, it could have been diagnosed some time ago and was in remission. She wasn't in a blast crisis. There were no progressive leukemic infiltrations, and she wasn't suffering from any significant infections."

Hanowell looked perplexed. "Then what killed her?"

"I don't know," I admitted.

"Drugs?" Wesley asked, making notes.

"The tox lab is beginning its second round of testing," I answered. "Her preliminary report shows a blood alcohol of point zero-three. In addition, she had dextro-methorphan on board, which is an antitussive found in numerous over-the-counter cough suppressants. At the scene we found a bottle of Robitussin on top of the sink inside her upstairs bathroom. It was more than half full."

"So that didn't do it," Wesley muttered to himself.

"The entire bottle wouldn't do it," I told him, adding, "It's puzzling, I agree."

"You'll keep me posted? Let me know what turns up on her," Wesley said. More pages turned, and he went to the next item on his agenda. "Roy's examined the fibers from Beryl Madison's case. We want to talk to you about that. And then, Pete, Kay"-he glanced up at us-"I have another matter to take up with both of you."

Wesley looked anything but happy, and I had the feeling that his reason for summoning us here wasn't going to make me happy, either. Hanowell, in contrast, was his usual unperturbed self. His hair, eyebrows, and eyes were gray. Even his suit was gray. Whenever I saw him, he always looked half asleep and gray, so colorless and calm I was tempted to wonder if he had a blood pressure.

"With one exception," Hanowell laconically began, "the fibers I was asked to look at, Dr. Scarpetta, reveal few surprises-no unusual dyes or shapes at cross sections to speak of. I have concluded that the six nylon fibers most likely came from six different origins, just as your examiner in Richmond and I discussed. Four of them are consistent with the fabrics used in automobile carpeting."

"How do you figure that?" Marino asked.

"Nylon upholstery and carpeting degrade very quickly in sunlight and heat, as you might imagine," Hanowell said. "If the fibers aren't treated with a premetalized dye, thereby adding UV and thermal stabilizers, car carpet will bleach out or rot in short order. By using X-ray fluorescence I was able to detect trace amounts of metals in four of the nylon fibers. Though I can't say with certainty the origin of these fibers is car carpeting, they are consistent with that."

"Any chance of tracing them back to a make and model?" Marino wanted to know.

"I'm afraid not," Hanowell replied. "Unless we're talking about a very unusual fiber with a patented modification ratio, tracing the darn thing back to a manufacturer is pretty futile, especially if the vehicles in question were manufactured in Japan. Let me give you an example. The precursor to the carpeting in a Toyota is plastic pellets, which are shipped from this country to Japan. There they are spun into fibers, the yarn shipped back here to be made into carpet. The carpet is then sent back to Japan to be placed inside the cars coming off the line."

He droned on. It only got more hopeless. "We also have headaches with cars manufactured in the United States. Chrysler Corporation, for example, may procure a certain color for its carpeting from three different suppliers. Then halfway through the model year Chrysler may decide to change suppliers. Let's say you and I are both driving 'eighty-seven black LeBarons with burgundy interior, Lieutenant. Well, the suppliers for the burgundy carpet in mine may be different from the suppliers in yours. Point is, the only significance of the nylon fibers I've examined is the variety. Two may be from household carpeting. Four may be from automobile carpeting. The colors and cross sections vary. You add to this the finding of olefin, Dynel, acrylic fibers, and what you've got is a hodgepodge I find most peculiar."

"Obviously," Wesley interjected, "the killer has a profession or some other preoccupation that puts him in contact with many different types of carpeting. And when he murdered Beryl Madison, he was wearing something that caused numerous fibers to adhere to him."

Wool, corduroy or flannel could account for that, I thought. But no wool or dyed cotton fibers had been found that were thought to have come from the killer.

"What about Dynel?" I asked.

"Usually associated with women's dresses. With wigs, fake furs," Hanowell answered.

"Yes, but not exclusively," I said. "A shirt or pair of slacks made of Dynel would build up static electricity like polyester, causing everything to stick to it. This might explain why he was carrying so much trace."

"Possibly," Hanowell said.

"So maybe the squirrel was wearing a wig," Marino proposed. "We know Beryl let him in her house, translated into she didn't feel threatened. Most ladies ain't going to feel threatened by a woman at the door."

"A transvestite?" Wesley suggested.

"Could be," Marino replied. "Some of the best-looking babes you'll ever see. It's friggin' sickening. Even I can't tell with a few of 'em unless I get right up in their faces."

"If the assailant were in drag," I pointed out, "how do we account for the fibers adhering to him? If the origin of the fibers is his workplace, certainly he wouldn't have been dressed in drag at work."

"Unless he works the streets in drag," Marino said. "He's in and out of Johns' rides all night long, maybe in and out of motel rooms with carpeted floors."

"Then his victim selection doesn't make any sense," I said.

"No, but the absence of seminal fluid might make sense," Marino argued. "Male transvestites, faggots, usually don't go around raping women."

"They usually don't go around murdering them, either," I answered.

"I mentioned an exception," Hanowell resumed, glancing at his watch. "This is the orange acrylic fiber you were so curious about."

His gray eyes fixed impassively on me.

"The three-leaf clover shape," I recalled.

"Yes," Hanowell said, nodding. "The shape is very unusual, the purpose, as is true with other trilobals, to hide dirt and scatter light. Only place I know you'll find fibers with this shape is in Plymouths manufactured in the late seventies-the fibers are in the nylon carpeting. They're the same three-leaf clover shape at cross section as the orange fiber in Beryl Madison's case."

"But the orange fiber is acrylic," I reminded him. "Not nylon."