“Oh yeah,” Lucy said. “As you probably know, that bathroom was a relatively modern addition built out from the master bedroom. And if you look at the marble walls, the cathedral ceiling we recovered, you can piece together this really narrow, sharply defined V pattern, with the apex pointing somewhere in the middle of the floor, most likely where the rug was, meaning the fire developed really fast and hot in that one spot.”

“Let’s talk about this famous rug,” Marino said. “You light it, and what kind of fire do we get?”

“A lazy flame,” Lucy answered. “Maybe two feet tall.”

“Well, that didn’t do it,” I said.

“And what’s also really telling,” she went on, “is the destruction to the roof directly above. Now we’re talking flames at least eight feet high above the fire’s origin, with the temperature reaching about eighteen hundred degrees for the glass in the skylight to melt. About eighty-eight percent of all arsons are up from the floor, in other words the radiant heat flux . . .”

“What the hell’s radiant flux?” Marino wanted to know.

“Radiant heat is in the form of an electromagnetic wave, and is emitted from a flame almost equally in all directions, three hundred and sixty degrees. Following me so far?”

“Okay,” I said.

“A flame also emits heat in the form of hot gases, which weigh less than air, so up they go,” Lucy, the physicist, went on. “A convective transfer of heat, in other words. And in the early stages of the fire, most of the heat transfer is convective. It moves up from its point of origin. In this case, the floor. But after the fire was going for a while and hot gas-smoke layers formed, the dominant form of heat transfer became radiant. It was at this stage that I think the shower door fatigued and fell on top of the body.”

“And what about the body?” I asked. “Where would that have been during all this?”

Lucy grabbed a legal pad off the top of a box and clicked open a pen. She drew the outline of a room with a tub and shower and, in the middle of the floor, a tall narrow fire that was impinging upon the ceiling.

“If the fire was energetic enough to project flames to the ceiling, then we’re talking about a high radiant flux. The body was going to be severely damaged unless there was a barrier between it and the fire. Something that absorbed radiant heat and energy—the tub and shower door—which would have protected areas of the body. I also think the body was at least some small distance from the point of origin. We could be talking feet, maybe a yard or two.”

“I don’t see any other way it could have happened,” I agreed. “Clearly something protected much of it.”

“Right.”