SACHS AND PULASKI dressed in hooded baby blue Tyvek jumpsuits, masks, booties and safety glasses. As Rhyme had always instructed, they each wrapped a rubber band around the feet, to make differentiating their footprints from the others easier. Then, encircling her waist with a belt, to which were attached her radio/video transmitter and weapon, Sachs stepped over the yellow tape, the maneuver sending some jolts of pain through her arthritic joints. On humid days or after a bout of running a tough scene or a foot pursuit, the knees or hips screaming, she harbored secret envy of Lincoln Rhyme's numbness. She'd never utter the thought aloud, of course, never even gave the crazy idea more than a second or two in her mind, but there it was. Advantages in all conditions.

She paused on the sidewalk, all by herself within the deadly perimeter. When Rhyme had been head of Investigation Resources-the outfit at NYPD in charge of crime scenes-he ordered his forensic people to search alone, unless the scene was particularly large. He did this because you tended psychologically to be less conscientious with other searchers present, since you were aware there was always a backup to find something you missed. The other problem was that just as criminals left behind evidence, crime scene searchers, however swaddled in protective gear, did too. This contamination could ruin the case. The more searchers, the greater that risk.

She looked into the gaping black doorway, smoke still escaping, and then considered the gun on her hip. Metal.

The lines're dead…

Well, get going, she told herself. The sooner you walk the grid after a crime, the better the quality of the evidence. Dots of sweat, full of helpful DNA, evaporated and became impossible to spot. Valuable fibers and hairs blew away, and irrelevant ones floated into the scene to confuse and mislead.

She slipped the microphone into her ear, inside the hood, and adjusted the stalk mike. She clicked the transmitter at her side and heard Rhyme's voice through the headset. "… you there, Sachs? Are… okay, you're online. Was wondering. What's that?" he asked.

He was seeing the same things she was, thanks to a small, high-definition video camera on a headband. She realized she was unintentionally looking at the hole burned into the pole. She explained to him what had happened: the spark, the molten raindrops.

Rhyme was silent for a moment. Then he said, "That's quite a weapon… Well, let's get going. Walk the grid."

There were several ways to search crime scenes. One popular approach was to begin in the outside corner and walk in an increasingly smaller concentric circle until you reached the center.

But Lincoln Rhyme preferred the grid pattern. He sometimes told students to think of walking the grid as if mowing a lawn-only doing so twice. You walked along a straight line down one side of the scene to the other, then turned around, stepped a foot or so to the left or right and went back in the direction you'd just come. Then, once you'd finished, you turned perpendicular to the lines you first walked and started all over again, doing the same back-and-forth.

Rhyme insisted on this redundancy because the first search of a scene was crucial. If you did a cursory examination initially you subtly convinced yourself that there was nothing to be found. Subsequent searches were largely useless.

Sachs reflected on the irony: She was about to walk the grid in part of a very different grid. She'd have to share that with Rhyme-but later. Now she needed to concentrate.

Crime scene work was a scavenger hunt. The goal was simple: to find something, anything left behind by the perp-and something would have been left behind. The French criminalist Edmond Locard nearly a hundred years earlier had said that whenever a crime occurred there was a transfer of some evidence between the perpetrator and the crime scene or the victim. It might be virtually impossible to see, but it was there to find if you knew how to look and if you were patient and diligent.

Amelia Sachs now began this search, starting outside the substation, with the weapon: the dangling cable.

"Looks like he-"

"Or they," Rhyme corrected through the headset. "If Justice For is behind this, they might have a sizeable membership."

"Good point, Rhyme." He was making sure she didn't fall into the number-one problem crime scene searchers suffered from: failure to keep an open mind. A body, blood and a hot pistol suggested that the victim was shot to death. But if you got it into your head that that was the case, you might miss the knife that was actually used.

She continued, "Well, he or they rigged it from inside. But I'd think he had to be outside here on the sidewalk at some point to check distances and angles."

"To aim it at the bus?"

"Exactly."

"Okay, keep going-the sidewalk, then."

She did, staring at the ground. "Cigarette butts, beer caps. Nothing near the door or the window with the cable, though."

"Don't bother with them. He's not going to be smoking or drinking on the job. He's too smart-considering how he put this whole thing together. But there'd be some trace where he stood. Close to the building."

"There's a ledge, see it?" She was looking down at a low stone shelf about three feet above the sidewalk. The top was set with spikes to keep pigeons, and humans, from perching there, but you could use it as a step if you wanted to reach something in the window. "Got some footprints, on the ledge. Not enough for electrostatic."

"Let's see."

She bent her head down and leaned forward. He was looking at what she was: shapes that could be toe marks of shoes close to the building.

"You can't get prints?"

"No. Not clear enough. But looking at them I'd say they're probably men's. Wide, square toes, but that's all I can see. No soles or heels. But it tells us that if there's a 'they' involved, it was probably just a 'he' rigging the trap outside."

She continued to examine the sidewalk and found no items of physical evidence that seemed relevant.

"Get trace, Sachs, and then search inside the substation."

At her instruction, the other two techs from Queens set up powerful halogen lights just inside the door. She took pictures and then collected trace on the sidewalk and the ledge near the cable.

"And don't forget-" Rhyme began.

"Substrata."

"Ah, one step ahead of me, Sachs."

Not really, she reflected, since he'd been her mentor for years and if she hadn't picked up his procedures for walking the grid by now, she had no business in crime scene work. She now moved to an area just outside the perimeter and took a second rolling-substrata, control samples to compare to the first. Any difference between what was collected at some distance from the scene and at the spot where the UNSUB was known to have stood might be unique to him or his dwelling.

Might not, of course… but that was the nature of crime scene work. Nothing was ever certain, but you did what you could, you did what you had to.

Sachs handed off the bagged evidence to the technicians. She waved to the Algonquin supervisor she'd spoken to earlier.

The field supervisor, just as solemn as before, hurried over. "Yes, Detective?"

"I'm going to search inside now. Can you tell me exactly what to look for-how he rigged the cable? I need to find where he stood, what he touched."

"Let me find somebody who does regular maintenance here." He looked over the workers. Then he called to another man, in dark blue Algonquin Consolidated Power overalls. A yellow hardhat. The worker tossed aside his cigarette and joined them. The field supervisor introduced them and told him Sachs's request.

"Yes, ma'am," he said, his eyes leaving the substation for an excursion across Sachs's chest, even though her figure was largely hidden by her billowy blue Tyvek jumpsuit. She thought about glancing down at his excessive belly but of course she didn't. Dogs pee where you don't want them to; you can't correct them all the time.