CLEANING HIS LATEX gloves with the pet-hair roller-and drawing an approving look from Rhyme-the young officer hefted the access door and surrounding frame, still connected. The door was about eighteen inches square and the frame added another two or so inches. It was painted dark gray.

Sachs was right. It was a tight fit. The UNSUB very likely would have sloughed off something from his body as he entered the substation.

The door opened with four small turn latches on both sides. They would have been awkward to loosen with a gloved hand, so there was a chance he'd used bare fingers, especially since he'd planned on blowing up the door with the battery bomb and destroying evidence.

Fingerprints fell into one of three categories. Visible (the sort left by a bloody thumb on a white wall), impressible (left in pliable material, like plastic explosive), and latent (hidden to the unaided eye). There were dozens of good ways to raise latent prints but one of the best, on metal surfaces, was simply to use store-bought Super Glue, cyanoacrylate. The object would be put in an airtight enclosure with a container of the glue, which would then be heated until it turned gaseous. The vapors would bond with any number of substances left by the finger-amino and lactic acids, glucose, potassium and carbon trioxide-and the resulting reaction created a visible print.

The process could work miracles, raising prints that were completely invisible before.

Except not in this case.

"Nothing," Pulaski said, discouraged, peering at the access door through a very Sherlock Holmesian magnifier. "Only glove smudges."

"Not surprising. He's been fairly careful so far. Well, collect trace from the inside of the frame, where he made contact."

Pulaski did this, using a soft brush over the newsprint examination sheets and taking swabs. He placed whatever he found-to Rhyme it seemed like very little-into bags and organized them for Cooper to analyze.

Sellitto took a call and then said, "Hold on. You're being speakered."

"Hello?" came the voice.

Rhyme glanced at Sellitto. "Who?" he whispered.

"Szarnek."

The NYPD Computer Crimes expert.

"What do you have for us, Rodney?"

Rock music clattered around in the background. "I can almost guarantee that whoever played with the Algonquin servers had the pass codes up front. In fact, I will guarantee that. First of all, we found no evidence of any attempted intrusion. No brute force attack. No shredded code of rootkits, suspicious drivers or kernel modules or-"

"Just the bottom line, you don't mind."

"Okay, what I'm saying is we looked at every port…" He hesitated at Rhyme's sigh. "Ah, bottom line. It was and wasn't an inside job."

"Which means?" Rhyme grumbled.

"The attack was from outside Algonquin's physical building."

"We know that."

"But the perp had to get the codes from inside headquarters in Queens. Either him or an accomplice. They're kept in hard copies and on a random code generator that's isolated from networks."

"So," the criminalist summarized, just to make sure, "no outside hackers, domestic or international."

"Next to impossible. I'm serious, Lincoln. Not a single rootkit-"

"Got it, Rodney. Any trace on his line from the coffee shop?"

"Prepaid cell connecting through a USB port. Went through a proxy in Europe."

Rhyme was tech enough to know that this meant the answer to his question was no.

"Thanks, Rodney. How do you get any work done with that music?"

The man chuckled. "Call me anytime."

The raucous hammering disappeared with the disconnecting click.

Cooper too was on the phone. He hung up and said, "I've found somebody in Materials Analysis at HQ. She's got a geology background. She knows a lot of the schools that have regular exhibits for the public. She's checking on volcanic ash and lava."

Pulaski, poring over the door, squinted. "Got something here, I think."

He pointed to a portion of the door near the top latch. "It looks like he wiped it off." He grabbed the magnifying glass. "And there's a burr of metal. Sharp… I think he cut himself and bled."

"Really?" Rhyme was excited. There's nothing like DNA in forensic work.

Sellitto said, "But if he cleaned it off, does it still do us any good?"

Before Rhyme could offer anything, Pulaski, still hunched over his find, mused, "But what would he have to clean it off with? Maybe spit. That's as good as blood."

This was going to have been Rhyme's conclusion. "Use the ALS."

Alternative light sources can reveal bodily fluids like traces of saliva, semen and sweat, all of which contain DNA.

All law enforcement agencies were now taking samples of DNA of suspects in certain types of offenses-sex crimes, for instance-and many were going further than that. If their UNSUB had committed a swabbable offense, he'd be in the Combined DNA Index System database, CODIS.

A moment later Pulaski, wearing goggles, paused the wand over a portion of the access door where he'd spotted the smear. There was a tiny yellowish glow. He called, "Yessir, got something. Not much."

"Rookie, you know how many cells are in the human body?"

"Well… no, I don't."

"Over three trillion."

"That's a lot of-"

"And do you know how many are needed for a successful DNA sample?"

He said, "According to your book, Lincoln, about a hundred."

Rhyme lifted an eyebrow. "Impressive." Then he added, "You think you have a hundred cells there in that massive smear?"

"Probably, I would think."

"You sure do. Sachs, looks like your swimming expedition wasn't in vain. If the battery had blown, it would have destroyed the sample. Okay, Mel, show him how to collect it."

Pulaski ceded the tricky task to Cooper.

"STR?" Rhyme asked the tech. "Or is the sample degraded?"

The polymerase chain reaction short tandem repeat method was the standard DNA test in criminal cases. It was fast and the most reliable system, with at least a billion to one accuracy. It could also determine the sex of the person from whom the sample came. But while the sample could be very small it had to be in good shape. If it had been damaged by the water or heat in the substation, a different test-mitochondrial DNA-would have to be used, a technique that took longer.

"I think it'll be fine." The tech collected the DNA and called the lab for pickup. "I know-ASAP," he told Rhyme just as the criminalist had been about to crack the whip.

"And spare no expense."

"That coming out of your fee, Linc?" Sellitto grumbled.

"I give you my best customer discount, Lon. And a good find, Pulaski."

"Thanks, I-"

Having delivered enough compliments for the time being, Rhyme moved on, "What about the trace from the inside of the door, Mel? You know, we're not moving very quickly here."

Cooper took the samples and looked them over on the examining sheet or under the microscope. "Nothing that doesn't match the samplars and substrata… except this." It was a tiny pink dot.

"GC it," Rhyme ordered.

A short time later Mel was reading results from the gas chromatograph, the mass spectrometer and several other analyses. "We've got an acidic pH-about two-and citric acid and sucrose. Then… well, I'll put it up on the screen."

The words appeared: Quercetin 3-O-rutinoside-7-O-glucoside and chrysoeriol 6,8-di-C-glucoside (stellarin-2).

"Fine," Rhyme said impatiently. "Fruit juice. With that pH, it's probably lemon."

Pulaski couldn't help but laugh. "How did you know that? I'm sorry, how did you know?"

"You only get out of a task what you bring to it, Rookie. Do your homework! Remember that." He turned back to Cooper.

"Then vegetable oil of some sort, lots of salt and some compound that eludes me completely."