Known for her unflinching depictions of violence, Mo Hayder has Phoebe “Flea” Marley, a police diver, join series regular Det. Insp. Jack Caffery in Ritual (Reviews, July 14), the first in her new Walking Man series.

Why did you decide to focus on Flea instead of Jack Caffery in Ritual?

I was preoccupied with people who recover dead bodies from underwater—it can be incredibly dangerous, and there's also something very sinister about it. When I looked at U.K. police divers, I realized very few were female. There are lots of fictional representations of women in policing, but I thought it'd be interesting to see how a woman would fare if her job relied on physical strength.

You pay so much attention to forensics and police procedure in your work. What's your research process?

I've been lucky with the local police diving team, who've been very patient with me. And I decided I'd better speak whereof I knew, so I got myself PADI [Professional Association of Divers] qualified. Now I've got real respect for deep water.

You often confront violence head on. Are you ever criticized for your graphic depictions?

When I started writing, I was impatient with crime novels that used violent acts to springboard a story and yet never dealt in detail with the real horror of that violence. So I was always clear that I'd use as much space for violence as I'd use for other parts of the narrative. Of course, I'm often criticized for it. But I wonder if people aren't only criticizing the violence but also that my moral stance isn't always felt clearly through the narrative. I don't contextualize the horror. I simply present the facts of the story and allow the reader to make the judgment.

What role does your background in film play?

For Birdman, my first novel, I drew on my knowledge of cinema and traditional ways to establish scenes: whether to start off with a close scrutiny of a character or start wide with an establishing shot. I also tend to use fewer interior monologues than many thriller writers. I try to let the characters' actions and dialogue do that job. That's a very cinematographic technique.

What's next for you?

The characters' stories in the new Walking Man books are so complete in my head that for the time being I'm going to keep going with the series. I'd like to do a stand-alone in the middle, just to break it up. Something set in the U.S. or Africa, maybe.