I did not remind her of the obvious. The police had found Fred Cheney's wallet in the glove compartment, complete with credit cards and thirty-five dollars cash. It dd not appear that the young couples' luggage had been gone through. As far as anyone could tell, nothing was missing from the Jeep except its occupants and Deborah's purse.

"The way the first dog acted," she went on matter-of-factly. "I assume this is unusual. Something frightened. Upset him, at any rate. A different smell - not the same scent the other dog picked up. The seat where Debbie may have been sitting…"

Her voice trailed off as she met my eyes.

"Yes. It appears that the two dogs picked up different scents."

"Dr. Scarpetta, I'm asking you to be direct with me."

Her voice trembled. "Don't spare my feelings. Please. I know the dog wouldn't have gotten so upset unless there was a reason. Certainly, your work has exposed you to search-and-rescue efforts, to bloodhounds. Have you ever seen this before, the way the dog reacted?"

I had. Twice. Once was when a bloodhound sniffed car trunk that, as it turned out, had been used to transport a murder victim whose body had been found inside a Dumpster. The other was when a scent led to an area along a hiking trail where a woman had been raped and shot.

What I said was "Bloodhounds tend to have strong reactions to pheromonal scents."

"I beg your pardon?"

She looked bewildered.

"Secretions. Animals, insects, secrete chemicals. Sex attractants, for example," I dispassionately explained. "You're familiar with dogs-marking their territory or attacking when they smell fear?"

She just stared at me.

"When someone is sexually aroused, anxious, or afraid, there are various hormonal changes that occur in the body. It is theorized that scent-discriminating animals, such as bloodhounds, can smell the pheromones, or chemicals, that special glands in our bodies secrete - "