She froze.

"Sachs!"

"Shhh." She had to concentrate. By moving a few inches at a time she was able to keep the waves below the top of the power source. But she could see she had no more than one or two minutes until the water hit the leads.

With a straight-bladed screwdriver she began to remove the frame holding the access door.

The water was now nearly to the top of the battery. Every time she leaned forward to get leverage to unscrew the paint-stuck hardware, another small tide rose and the murky water sloshed up onto the top of the battery before receding.

The battery's voltage was certainly smaller than the hundred-thousand-volt line that had produced the arc flash outside, but the UNSUB probably didn't need to cause that much damage. His point was to create a big enough explosion to destroy the access door and whatever evidence it contained.

She wanted the damn door.

"Sachs?" Rhyme whispered.

Ignoring him. And ignoring the image of the cauterized holes in the smooth flesh of the victim, the molten teardrops…

Finally the last screw came out. Old paint held the door frame in place. She jammed the tip of the screwdriver into the edge and slammed her hand onto the butt of the tool. With a crack, the metal came away in her hands. The door and frame were heavier than she'd thought and she nearly dropped it. But then she steadied herself, without sending a tsunami over the battery.

In the opening she saw the narrow utility tunnel that the suspect would have used to sneak into the substation.

Rhyme whispered urgently, "Into the tunnel. It'll protect you. Hurry!"

"I'm trying."

Except the access door wouldn't fit through the opening, even diagonally, because the frame was attached. "Can't do it," she said, explaining the problem. "I'll go back up the stairs."

"No, Sachs. Just leave the door. Get out through the tunnel."

"It's too good a piece of evidence."

Clutching the access door, she began her escape, wading toward the stairs, glancing back from time to time to keep an eye on the battery. She moved agonizingly slowly. Even so, every step sent another wave cresting to the edge of the battery terminals.

"What's going on, Sachs?"

"I'm nearly there," she whispered, as if too loud a voice would create more turbulence in the water.

She was halfway to the steps when the water rose in tiny eddies and swirled around first one terminal, then the next.

No arc flash.

Nothing.

Her shoulders sagged, heart thumping.

"It's a dud, Rhyme. We didn't have to worr-"

A burst of white light filled her vision, accompanied by a huge cracking roar, and Amelia Sachs was flung backward, under the surface of the grim ocean.

The aide hurried into the room, looking Rhyme over carefully. "What's wrong? How're you feeling?"

"It's not me," his boss snapped, eyes wide, nodding his head at the blank screen. "Amelia. She was at a scene. A battery… another arc flash. The audio and video are out. Call Pulaski! Call somebody!"

Thom Reston's eyes narrowed with concern but he had practiced the art of caregiving for a long time; no matter what the crisis, he would coolly go about his necessary tasks. He calmly picked up a landline phone, regarded the number pad nearby and hit a speed-dial button.

Panic isn't centered in the gut, and it doesn't trickle down the spine like, well, electricity in an energized wire. Panic rattles the body and soul everywhere, even if you're numb otherwise. Rhyme was furious with himself. He should have ordered Sachs out the instant they saw the battery, the rising tide. He always did this, got so focused on the case, the goal, finding the tiny fiber, the fragment of friction ridge print, anything that moved him closer to the perp… that he forgot the implications: He was playing with human lives.

Why, look at his own injury. He'd been a captain in the NYPD, the head of Investigation Resources, and was searching a crime scene himself, crouching to pick up a fiber from a body when the beam tumbled from above and changed his life forever.

And now that same attitude-which he'd instilled in Amelia Sachs-might have done even worse: She could now be dead.

Thom had gotten through on the line.

"Who?" Rhyme demanded, glaring at the aide. "Who're you talking to? Is she all right?"

Thom held up a hand.

"What does that mean? What could that possibly mean?" Rhyme felt a trickle of sweat down his forehead. He was aware his breath was coming faster. His heart was pounding, though he sensed this in his jaw and neck, not his chest, of course.

Thom said, "It's Ron. He's at the substation."

"I know where the fuck he is. What's going on?"

"There's been… an incident. That's what they're saying."

Incident…

"Where's Amelia?"

"They're checking. There're some people inside. They heard an explosion."

"I know there was an explosion. I fucking saw it!"

The aide's eyes swiveled toward Rhyme. "Are you… how are you feeling?"

"Quit asking that. What's going on at the scene?"

Thom continued to scan Rhyme's face. "You're flushed."

"I'm fine," the criminalist said calmly-to get the young man to focus on his phone call. "Really."

Then the aide's head tilted sideways and to Rhyme's horror he stiffened. His shoulders rose slightly.

No…

"Okay," Thom said into the phone.

"Okay what?" the criminalist snapped.

Thom ignored his boss. "Give me the information." And, cradling the phone between neck and shoulder, he began to type on the keyboard of the lab's main computer.

The screen popped to life.

Rhyme had lost the pretense of calm and was about to lose his temper when, on the screen, up came the image of an apparently uninjured, though very wet, Amelia Sachs. Strands of her red hair were plastered around her face like seaweed on a surfacing scuba diver.

"Sorry, Rhyme, lost the main camera when I went under." She coughed hard and wiped at her forehead, examined her fingers with a look of distaste. The motion was jerky.

Relief immediately replaced panic, though the anger-at himself-remained.

Sachs was staring back, somewhat eerily, her eyes focused only in his general direction. "I'm on one of the Algonquin workers' laptops. It's got a camera set up on it. Can you see me okay?"

"Yes, yes. But you're all right?"

"Just took in some pretty disgusting water through my nose. But I'm okay."

Rhyme was asking, "What happened? The arc flash…"

"It wasn't an arc. The battery wasn't rigged for that. The Algonquin guy told me there wasn't enough voltage. What the UNSUB did was make a bomb. Apparently you can do that with batteries. You seal the vents and overcharge it. That produces hydrogen gas. When water hits the terminals, it short-circuits and the spark ignites the hydrogen. That's what happened."

"And have the medics looked you over?"

"No, no need. The bang was loud but it wasn't that big. I got hit by some bits of plastic from the housing. Didn't even bruise me. The impact knocked me down but I kept the access door above the water. I don't think it's contaminated too bad."

"Good, Ame-" His voice braked to a halt. For some reason, years ago they'd settled on an unspoken superstition: They never used their first names. He was troubled that he nearly had. "Good. So that's how he got in."

"Had to be."

It was then that he was aware of Thom walking toward the wall. The aide grabbed the blood pressure monitor and wrapped it around Rhyme's arm.

"Don't do that-"

"Quiet," Thom barked, silencing Rhyme. "You're flushed and you're sweating."

"Because we just had a fucking incident at a crime scene, Thom."