LAPD K-9 Officer Scott James and German shepherd Maggie, the stars of Crais’s The Suspect, join Elvis Cole and Joe Pike, the author’s series leads, in The Promise.

How challenging was it to meld these casts of characters?

Having Elvis and Joe team up with Scott and Maggie was natural. I love writing about Elvis and Joe, and I had these wonderful new characters, Scott James and Maggie, so bringing them all together was inevitable. I was still writing Suspect when story and scene ideas began spooling up for The Promise: how Elvis and Scott might meet, and the incredible fun I could have bringing Maggie together with Elvis’s cat. All I needed was the right story, and once I had it, the novel exploded.

You heard from a lot of new fans because of Maggie after The Suspect was published.

The popularity of Suspect ran far beyond the thriller community. Maggie cut across genres and boundaries. People who love dogs spread the word to other dog lovers, and even nonreaders were snapping up the book. People sent pictures of their dogs, and police K-9 officers and military K-9 handlers sent pictures of their K-9 partners. Some K-9 officers and their dogs came to my signings. I’d put them in the show and let them demonstrate what their dogs could do. It was touching and beautiful. People see their own dogs in Maggie, or Maggie in their own dogs.

How did you research such things as bomb-squad protocols, K-9 Corps training, and intra–government agency pecking orders?

LAPD has always been open and accessible when I’ve researched my novels. The K-9 Platoon was enormously helpful when I researched Suspect. Often when I’m writing, the story and characters take me into areas I know nothing about. I’ll make up something on the fly to keep rolling, and fact-check later. I’m usually pretty close. Creating fiction that feels real to the reader is important, but reality isn’t a prison. I’m not writing nonfiction. I won’t let facts and procedure stand in the way of making my characters and story more exciting and interesting.

Was it a conscious choice to lend Joe Pike, the stoic, tight-lipped partner to Elvis Cole, a rather small presence in The Promise?

Pike was going to have a larger role, but as I got deeper into the story and learned more about the Amy Breslyn, the woman who lost her son to a terrorist bombing, Jon Stone loomed larger and larger, and finally took over. I was surprised at first, until I realized Jon’s connection to Amy Breslyn was true to the nature of the book; Jon’s feelings for Amy Breslyn and her loss became the heart of it. But Pike’s fans shouldn’t worry. I’m thinking my next book might be another Joe Pike novel.