O’Brien draws on his service as a medic in Afghanistan for his debut, Fire in the Blood (Random House, Aug.).

How did this novel come about?

While serving in Afghanistan, I knew soldiers who suffered tragedies back home, and were given two weeks of emergency leave to attend to their affairs. It seemed so surreal and heartbreaking—both that any of us would lose someone back home, and to get this break from war to go contend with that. And as someone who grew up reading detective fiction, I started wondering how it would be if the death was under mysterious circumstances. I’ve been a lover of crime fiction since I was a kid, but it wasn’t until I joined the army that it became clear to me how naturally related the topics were. After I got back from Afghanistan, I began to see crime fiction—and classic detective fiction in particular—in a new light. All these stories of isolated men with vague, violent pasts. And, of course, many great crime writers were veterans themselves.

What was it like translating your experiences in Afghanistan into fiction?

Fire in the Blood is certainly informed by my time as a soldier, but I was clear from the beginning that I wasn’t interested in lightly fictionalizing my own life. Because direct experience of war has become rare for Americans, I think there’s a natural tendency to assume that war fiction written by veterans is more autobiographical. But the journey of my lead, Coop, is fiction, and for me as a writer, my experiences simply made the monumental and deeply rewarding task of storytelling a little easier.

Why make Coop a sapper?

I thought his experience as a combat engineer would give him skills that later come into play, both in a general sense—an aptitude for hunting down things that have been hidden—but also specific skills, like opening a locked door with bump keys or fixing a damaged cell phone.

Did you set the book in 2003 because that’s when you were in Afghanistan?

Probably in the beginning. As I got further from 2003, it felt more and more urgent to capture that time—the politics, the energy, how utterly unprepared we were for war. Unfortunately, for our country and the world, a similar version of this book could have been set now, since we’re still sending young people to fight in Afghanistan. In general, I think most political art is bad art and bad politics. I was careful not to let the characters or plot become a political parable. It was only after I finished that I saw all the ways my values were suffused in the book.