Hollywood to the contrary, it was a highly unusual accident. Automobiles did not routinely turn into fireballs under any circumstances, and this one, his trained eyes saw at once, should not have been all that serious. Okay, there was one unavoidable fatality from the crash itself, the girl in the death seat of the first Cresta, who'd been nearly decapitated. But not the rest, there was no obvious reason for them. The first Cresta had rear-ended the truck at …forty or fifty miles of differential speed. Both air bags had deployed, and one of them ought to have saved the driver of the first car, he saw. The second car had hit at about a thirty-degree angle to the first. Damned fool of a cop to make a mistake like that, Nicholson thought. But the wife hadn't been belted in…maybe she'd been attending to the kids in the back and distracted her husband. Such things happened, and nobody could undo it now.

Of the six victims, one had been killed by collision, and the other five by fire. That wasn't supposed to happen. Cars were not supposed to burn, and so Nicholson had his people reactivate a crossover half a mile back on the Interstate so that the three accident vehicles could remain in place for a while. He got on his car radio to order up additional accident investigators from Nashville, and to recommend notifying the local office of the National Transportation Safety Board. As it happened, one of the local employees of that federal agency lived close to Oak Ridge. The engineer, Rebecca Upton, was on the scene thirty minutes after receiving her call. A mechanical engineer and graduate of the nearby University of Tennessee, who'd been studying this morning for her PE exam, she donned her brand-new official coveralls and started crawling around the wreckage while the tow-truck operators waited impatiently, even before the backup police team arrived from Nashville. Twenty-four, petite, and red-haired, she came out from under the once-red Cresta with her freckled skin smudged, and her green eyes teary from the lingering gasoline fumes. Sergeant Nicholson handed over a Styrofoam cup of coffee that he'd gotten from a fireman.

"What do you think, ma'am?" Nicholson asked, wondering if she knew anything. She looked like she did, he thought, and she wasn't afraid to get her clothes dirty, a hopeful sign.

"Both gas tanks." She pointed. "That one was sheared clean off. The other one was crumpled by the impact and failed. How fast was it?"

"The collision, you mean?" Nicholson shook his head. "Not that fast. Ballpark guess, forty to fifty."

"I think you're right. The gas tanks have structural-integrity standards, and this crash shouldn't have exceeded them." She took the proffered handkerchief and wiped her face. "Thanks, Sergeant." She sipped her coffee and looked back at the wrecks, wondering.

"What are you thinking?"

Ms. Upton turned back. "I'm thinking that six people—"

"Five," Nicholson corrected. "The trucker got one kid out."