When the boys were out of earshot, the four adults moved into the living room, taking coffee and tea with them. The house was warm and quiet, except for Brewster’s snoring from his seat of honor on Ruth’s lap. Savich began, “So Dix, you told us the doctor at Loudoun County Community Hospital did a toxicology screen on Ruth when she was admitted. You hear from him yet?”

Dix nodded. “Actually, it was the ME who called earlier. He ran what was left of your blood sample, Ruth. You had the same drug in your system that Erin Bushnell did—a drug called BZ.”

Sherlock said, “I don’t know much about it except I think it’s a gas they used in Vietnam that affects the nervous system. Did he tell you more about it, Sheriff?”

Dix paused for a moment, smiled at her. “Actually, Sherlock, while Savich’s corn on the cob was boiling, I googled it on the Internet. I printed some of it out, so you can look at it later. It’s officially called quinuclidinyl benzilate, but for obvious reasons it’s known simply as BZ. It’s a colorless and odorless gas that’s usually delivered as an aerosol and was developed for the military in the 1960s. It works fairly quickly, causing increased heart rate, blurry vision, lack of coordination. The unusual thing is that it’s what they call a psychochemical—it affects perception and thought, causes hallucinations, confusion, forgetfulness, and eventually stupor.

“BZ didn’t turn out to be much use in war, though, because the effects are unpredictable, ranging from overwhelming fear and panic to all-out rage that led exposed soldiers to attack without regard for their own safety.

“The Russians used an agent similar to BZ against the Afghan guerrillas during the eighties, and get this—it’s possible they pumped this gas into that theater during the hostage crisis in Moscow, probably in really high concentrations because they ended up with hundreds of people dead.”

“But Erin wasn’t dead when she was stabbed,” Sherlock said.

“No, but there was a lot of it in her system, more than in yours, Ruth. From what you told us about how terrifying it was for you in that cave chamber, how you were imagining God knows what coming after you, I hate to think what Erin Bushnell went through.”

Ruth let out a long breath. “So I guess I didn’t just go crazy. But how does anyone get ahold of a gas like this?”

Dix shrugged. “The ME said chemicals like this are available from pharmaceutical companies and on the Internet. Apparently they have some legitimate uses for research. It’s unusual enough to warrant looking into but it’s unlikely the BZ is from a nice, clean local source that would identify our killer.”

Savich nodded. “Since you got a lower dose than Erin, Ruth, you probably got the residue from the gas he used on her. Maybe he came back later to check on his handiwork and found you, freaked out, maybe unconscious. Maybe he bashed you on the head or he found you already injured, and hauled you out of there.”

“But why not simply kill me and leave me in there with Erin?”

Savich said slowly, “Because that was her tomb, Ruth, not yours. All hers.”

“That would be really sick, Dillon.”

“Yes,” he said, “it would be.”

Sherlock sat forward, her teacup balanced on her knee. “So you think this tomb idea has something to do with his embalming her?”

Dix said, “Dr. Himple said he didn’t actually embalm her. He said it was the strangest thing he’d ever seen. I’ll try to explain this correctly.” Dix pulled a sheet of paper out of his shirt pocket, perused it for a moment. “Okay, when a funeral home embalms a body, they make small incisions in the carotid artery and the jugular vein, thread a tube into the carotid to pump in the embalming fluid, and drain the blood out through the jugular vein. It takes about three gallons of embalming fluid to thoroughly disinfect and preserve a body. They also put fluid in the body cavities, a mixture of formaldehyde, methanol, ethanol, and other solvents.

“The thing is, our murderer didn’t do a thorough job of it. He made the small incisions in her carotid and jugular, pumped in about a gallon of embalming fluid, let a bit of blood drain out the jugular vein, then called it a day.”

Sherlock said slowly, staring into the fireplace, “So he either didn’t know how to do the procedure correctly or it was some kind of ritual, enough to give him the taste of the process, to give him the satisfaction.”

Savich nodded. “Yes, and he posed her. He may have considered it part of a ceremony, probably done with a good deal of gravity on his part, almost reverence. He may have wanted to preserve the body for a while before he buried it somewhere.”