Q. In Her Defense brings to mind the works of John Gris ham, Scott Furrow, and Jonathan Harr's A Civil Action, all of which have captivated the reading public. What is it about the legal thriller that makes it a such compelling genre?

A. The legal thriller is the opportunity to raise all kinds of matters -- crime, politics, social justice, even those of the heart, and do justice in a satisfying, plausible way. In the end of the book you know you will find out the truth, whereas in the real world, in the news, even in famous trials, you are often denied that resolution. And let me add that since the ancient Greeks the public has loved and hated its lawyers. It's fun to see them triumph or get their just desserts.

Q. You start with a guy at the bottom, personally and professionally --he's getting divorced, living in a small sad apartment, representing two-bit drug offenders who can't afford a lawyer. And he gets the proverbial case of a life time -- a rich, beautiful client, accused of murder. Except there's a hitch, she confesses that she did it. Why that setup, why make her guilty?

A. After I left the Justice Department, I spent a lot of time in the cellblocks, representing poor clients who usually did it. People always asked, 'How can you defend someone who's guilty?' I rarely found their guilt so black and white, there was always something, some shade of gray, to build the case on. Trial lawyers are competitive people who like to win, and often that means a guilty person goes free, which can create a lot of angst. It's interesting to see how far a lawyer will go when he's motivated, and Frank O'Connell is very motivated. Aside from the usual reasons, he's fallen in love with his client. Let me also say that I always found guilty clients more interesting.

Q. You were a prosecutor in the Criminal Section of the Civil Rights Division of the Justice Department in the 1970s. Without giving too much away, how much of what you did there made it into this book?

A. I worked on some of the Justice Department's most controversial matters. My first assignment was the shootings of Kent State students by Ohio National Guardsmen. My second was to investigate conspiracy theories in the assassination of Martin Luther King. Essentially, our job involved investigating and prosecuting people in power who trampled the rights of ordinary citizens. I don't want to give too much away, but the case that made it into the book concerned the time we investigated ourselves, and when it was over, I was testifying before a Senate Committee, and the President had to issue pardons.

Q. This is your first novel; was this something that was brewing for a long time?

A. No. I began it as an entertainment for myself, a change of pace from writing briefs and legal memos. And it was fun. With fiction there are no rules, no page limits, no client. You aren't constrained by a set of facts, only your own imagination. My wife liked the story, so I decided to try and have it published.

Q. Did that take a lot of plotting?

A. No. The story arose naturally. I had an opening line and a closing line and a central twist based on my experience at the Justice Department. I would write a bit, think about it, write some more and then put it away. It was something to do when I had spare time.

Stephen Horn was born in the Bronx, New York, and received an engineering degree from Rutgers University. He commanded an infantry company of the 101st Airborne Division in Vietnam. As a prosecutor in the justice Department's Civil Rights Division, he tried criminal cases and participated in some of the department's most famous investigations, including the killing of four Kent State students by the Ohio National Guard and the assassination of Dr. martin Luther King Jr. Now in the private practice of law, he lives outside Washington, D.C., with his wife and two children. In Her Defense is his first novel.