I was pregnant with my daughter when I started writing my first thriller, so I guess you could blame hormones. My husband and I were excited about having a kid—it was having a baby that had us worried. We had a lot to learn, so like good liberal arts graduates, we signed up for a class.

The subject was basically “How To Have a Baby and Keep It Alive the First Year.” It met once a week, for three hours, for 10 weeks. We should have gotten college credit for it. Mostly they just showed us childbirth videos. (They never went well. You know that scene from Alien where the alien bursts out of John Hurt's chest?) I think they were trying to numb all of us to the realities of the situation, so we wouldn't drop dead from shock in the delivery room. But my husband and I couldn't take it. We dropped out.

There must have been some sort of connection, because after that, I developed an unquenchable thirst for thrillers.

I guess I had gore on the brain.

I was obsessed with Val McDermid's Tony Hill and Carol Jordan books, delightfully twisted stuff. There were three at the time. If there had been a fourth, I probably wouldn't have written Heartsick.

I was already an author of three books by then. I had a contract to write my fourth, a Nancy Drew parody, Confessions of a Teen Sleuth. I had a deadline and an advance. I had things to do. Instead, I came up with the germ of an idea—a detective who'd led a task force that had hunted a beautiful female serial killer for 10 years, and the fallout of his obsession with her—and couldn't get it out of my head. I couldn't resist it. It became my adulterous novel on the side.

I worked in secret, without expectations. I just wanted to write the thing, to entertain myself, to see if I could do it, to bide time until the next Val McDermid book came out. Eventually, I had to come clean.

I told my husband, and my agent, about the affair.

They seemed okay with it.

Now that my thriller writing was out in the open, I embraced it tirelessly, editing every day. I wanted to make my tawdry liaison into something legitimate—I wanted to marry that floozy. I finished Heartsick with my daughter asleep in her bassinet by my desk, a feat that any new mother will tell you cannot be sufficiently praised.

Evil at Heart, the third book in that series, after Sweetheart, came out last September. I'm working on the fourth. My daughter is almost five now, old enough that she has taken to autographing copies of Evil at Heart when she joins me at promotions. She signs the dedication page, right under her name. It's only fair. If it hadn't been for her, I might never have embraced my joyous blood lust.

But she still can't read my books until she's 30.