Lee Child’s 16th novel featuring former military cop Jack Reacher, The Affair, takes Reacher back to 1997, when he left the Army and embarked on his traveling ways.

You’ve taken Reacher back in time once before, in The Enemy, the eighth book in the series. What prompted you to do it again?

Readers have always had two persistent questions: “What was Reacher like in the Army?” was answered in The Enemy, and now “Why did he leave the Army?” is answered in The Affair. It’s his last case in uniform.

A female character, Elizabeth Deveraux, has a major role in The Affair. Like many women before her, she never appears again in subsequent books. Why is that?

Partly that’s about Reacher himself. He’s always moving forward, never revisiting the past, reluctant to repeat experiences, cautious about settling in one place too long—and partly it’s about my choices as a series writer. I didn’t want to do a standard recurring-cast soap-opera type of series, so I almost never bring characters back. That choice has drawbacks, but it keeps the series fresh for me.

What parts of the Reacher stories do you enjoy writing the most?

Usually the fights, but in this one, it was the sex scenes. I feel like I finally figured out how to do it.

When asked about major influences, you often mention John D. MacDonald and his Travis McGee series. What is it about MacDonald and McGee?

I felt like MacDonald was pointing down the road I wanted to travel, and there was something about the McGee series that let me see the skeleton beneath the skin. On one level they were great stories, obviously, but on another they were how-to manuals for me.

It’s now been 16 novels with Reacher. Getting tired?

No, because the no-job, no-location structure gives me infinite flexibility. Reacher can get involved anywhere with anything. There’s no template, no fixed points—everything is a new challenge.

Is One Shot, the ninth in the series, still scheduled to begin shooting September 27 with Tom Cruise as Reacher?

Yes, and the September date is crucial to the opening sequence they have in mind, a truly great visual, better than the book, which showed me the quality of their thinking. Want to know what it is? See the movie!

Have you been closely involved in the movie’s planning?

Included, certainly, but not really involved. We talk all the time, but in the end I believe in letting people do their jobs.