You're about to publish your 21st Gregor Demarkian mystery, Hardscrabble Road. What's surprised you the most about how your detective has evolved?

When I started the series, it was supposed to be a contrast between Gregor, who was old-fashioned, and his love-interest, Bennis, who was more hip. He got more modern in his attitudes toward everything, except technology, but the series itself just got darker after I got darker. Gregor became a lot less sure that things were going to come out right, because in my own life, things hadn't.

How much of your own life is in your books?

It varies; no one ever tells the truth about themselves, because it's embarrassing, even if you're Leonardo da Vinci. There's a huge amount of me, for example, in Somebody Else's Music, but in True Believers, I was trying very hard to get into other people's heads, and so it's not necessarily me at all. It always bothers me when people don't distinguish between me and the characters I've created. I don't think I fit any of the current political labels—I'm a liberal when we're talking about most social issues, but a libertarian when it comes to others. Certainly my books express my belief that evil is something that's with us—that it's a real thing. That there are people who choose to view the world as if they are the only people in it. Like Gregor, I believe morality is not relative.

Has P.D. James influenced your work?

P.D. James is the only writer out there I wish I were. I would never have tried writing a mystery story if I hadn't read her. She showed me what you could do in the form, that it didn't have to be formulaic, that it didn't have to be restricted. My problem with a lot of detective fiction is that it's primarily about the detective, and that's interesting for about two books, and then any human being gets boring. You can't just do the same guy over and over again without readers getting tired of his neuroses. James's books concentrate so much on the other people involved in the case that they don't get stale.

Is fair play important to you, providing enough clues for readers to solve the crime?

It's pretty important—I don't want to cheat my readers. The clues should be there. The whodunit form is like a kind of sonnet—there are certain rules, certain expectations. You must fit your content into that framework, which includes making sure there's enough there for the reader to be able to figure it out, if not on a first reading, then on a second or third one.