When I finished my debut novel, The Last Dawn, I had no idea it would start a series, or even that I wanted it to. The ending I wrote did imply another book, but I blithely moved on to another project altogether. So it was no small surprise when my agent said she would not even shop the first novel unless I had a detailed synopsis for a sequel.

What to do? I knew only that I did not want to tame my badly wounded, occasionally out-of-control protagonist, Capt. Ajax Montoya. So rather than a plot per se, I searched for an opening that would bury the character in a morass of despair from which he’d have to climb before plunging into the chaos of the mystery at the heart of the story.

The first book was set in Nicaragua during the “bloody ’80s”—the revolutions, counterrevolutions, and civil wars that turned Central America into a graveyard. I had lived there as a freelance journalist for three years during this period, but, strangely, it had been a safe place, at least for foreigners. Neither the leftist Sandinistas nor the CIA-backed Contra rebels had any stake in killing Americans. El Salvador, on the other hand, was a truly frightening place—packed to the rafters with the dead and disappeared. I never liked working there and never went unless sent. Its right-wing government was controlled by the very people who—if they did not invent the term death squad—perfected the art of it. After the Marxist rebels they were fighting, the government and army counted journalists as some of their greatest foes, killing six of my colleagues over one horrible weekend in 1989. (I escaped unscathed, but over my shoulder, as I write this at my desk, there is a framed copy of the release form I was issued after being arrested there during a rebel offensive for “suspected collaboration with the terrorist forces of this country... the merits of which were not found to warrant further action.”)

So El Salvador in 1989 was the right place to set the next novel—a country caught up in a civil war that seemed more like full-blown psychosis than a conflict. And a place in which even my battle-hardened hero fears to tread, though against all advice he purses justice for a killing no one cares about.

These circumstances allow Ajax to exert the one characteristic all detectives—no matter how flawed—have in common, and for which readers and writers admire them so: an unfailing moral compass.