“Nothing, Rhyme. It’s like he’s wearing a Tyvek suit of his own. He’s just not leaving anything behind.”

Edmond Locard, the famed French criminalist, developed what he called the exchange principle, which stated that whenever a physical crime occurs, there is some transfer of evidence between the criminal and the location. He leaves something of himself at the scene and he takes some of the scene with him when he departs. The principle is deceptively optimistic, though, because sometimes the trace is so minuscule it’s missed and sometimes it’s easily located but provides no helpful leads for investigators. Still Locard’s principle holds that there would be some transfer of materials.

Rhyme often wondered, though, if there existed the rare criminal who was as smart as, or smarter than, Rhyme himself and if such a person could learn enough about forensic science to commit a crime and yet flaunt Locard’s principle—leave behind no evidence and pick up none himself. Was the Watchmaker such a person?

“Think, Sachs. . . . There’s got to be more. Something we’re missing. What does the vic say?”

“She’s pretty shaken up. Not really concentrating.”

After a pause Rhyme said, “I’m sending down our secret weapon.”

Kathryn Dance sat across from Lucy Richter in the living room of her apartment.

The soldier was beneath a Jimi Hendrix poster and a wedding photo of Lucy and her husband, a round-faced, cheerful man in a dress military uniform.

Dance noted the woman was pretty calm, considering the circumstances, though, as Amelia Sachs had said, something was clearly troubling her. Dance had the impression that it was partly something other than the attack. She didn’t exhibit the post-traumatic stress reactions of a near miss; she was troubled in a more fundamental way.

“If you don’t mind, could you go through the details again?”

“If it’ll help catch that son of a bitch, anything.” Lucy explained that she’d gone to the gym to work out that morning. When she returned she found the clock.

“I was upset. The ticking . . .” Her face now revealed a subtle fear reaction. Fight-or-flight. At Dance’s prompting she explained about the bombs overseas. “I guessed it was a present or something but it kind of freaked me out. Then I felt a breeze and went to look. I found the bedroom window open. That’s when the police showed up.”

“Nothing else unusual?”

“No. Not that I can remember.”

Danced asked her a number of other questions. Lucy Richter didn’t know Theodore Adams or Joanne Harper. She couldn’t think of anyone who’d want to hurt her. She’d been trying to recall something else that could help the police but was drawing a blank.

The woman was outwardly brave (“that son of a bitch”) but Dance believed that something in Lucy’s mind was preventing her, subconsciously, from focusing on what had just happened. The classic defensive crossing of her arms and legs was a sign, indicating not deception but a barrier against whatever was threatening her.