Where had my Passenger gone, and why? Would it come back? And these questions pulled me inevitably down into even more alarming speculation: What was the Passenger and why had it come to me in the first place?

It was somewhat sobering to realize just how deeply I had defined myself by something that was not actually me-or was it? Perhaps the entire persona of the Dark Passenger was no more than the sick construct of a damaged mind, a web spun to catch tiny glimmers of filtered reality and protect me from the awful truth of what I really am. It was possible. I am well aware of basic psychology, and I have assumed for quite some time that I am somewhere off the charts. That's fine with me; I get along very well without any shred of normal humanity to my name.

Or I had until now. But suddenly I was all alone in there, and things did not seem quite so hard-edged and certain. And for the first time, I truly needed to know. Of course, few jobs provide paid time off for introspection, even on a topic as important as missing Dark Passengers. No, Dexter must still lift that bale. Especially with Deborah cracking the whip.

Happily, it was mostly routine. I spent the morning with my fellow geeks combing through Halpern's apartment for some concrete residue of his guilt. Even more happily, the evidence was so abundant that very little real work was necessary.

In the back of his closet we found a sock with several drops of blood on it. Under the couch was a white canvas shoe with a matching blotch on top. In a plastic bag in the bathroom was a pair of pants with a singed cuff and even more blood, small dots of spray that had been heat-hardened.

It was probably a good thing that there was so much of it out in the open, because Dexter was truly not his usual bright and eager self today. I found myself drifting in an anxious gray mist and wondering if the Passenger was coming home, only to jerk back to the present, standing there in the closet holding a dirty, blood-spattered sock. If any real investigation had been necessary, I am not sure I could have performed up to my own very high standards.

Luckily, it wasn't needed. I had never before seen such an outpouring of clear and obvious evidence from somebody who had, after all, had several days to clean up. When I indulge in my own little hobby I am neat and tidy and forensically innocent within minutes; Halpern had let several days go by without taking even the most elementary precautions. It was almost too easy, and when we checked his car I dropped the "almost." Clearly displayed on the central armrest of the front seat was a thumbprint of dried blood.