A professor with dementia seeks a missing girl in John Katzenbach’s What Comes Next.

What inspired you to have the lead character suffer from degenerative dementia?

After an old and dear friend of mine was diagnosed with a frontal temporal lobe dementia, my research came across the Lewy body dementia that my character, Adrian Thomas, suffers. It is characterized by hallucinations. I thought, what if a person suffering from this disease saw a crime take place—and within moments I was writing the book.

What problems did your lead characters, a teenage girl and an elderly professor, present?

One of the most engaging aspects was building parallel stories between an old man facing his mortality and a young woman whose future was at risk. I wanted to find the sorts of inner resources that an old college professor facing a difficult death would have to call upon, at the same time that a teenage girl has to uncover strengths that she doesn’t know she possesses. I wanted to create two different clocks counting down in the same novel.

How did you research the creepy Web site?

As unsettling as the Web site that I invented is—where people buy in to watch the real-time confinement and psychological stress of a young woman—it’s got nothing on what’s out there. An old friend who used to work in cyber crime with the FBI told me, “Invent what you want, because 10 seconds after you come up with something, it’s already out-of-date.” The man and woman who run the site don’t think of themselves as criminals, but as entrepreneurs. If that’s not emblematic of this weird and modern world we live in, what is?

Why do you think you are you so popular in Europe?

European audiences seem to like a richness of storytelling. They enjoy being wrapped deeply into a plot and identifying strongly with characters. The questions I get from regular thriller fans in countries like Spain and Germany often sound like those I get after a speech to a group of psychiatry medical school residents. The Norwegians and Swedes really like twisted, emotionally tormented plots. Bless their hearts.

Does your background as a journalist still influence your writing?

It informs every word I write. I spent many happy Miami News and Miami Herald years covering crime and punishment, and I thought, never could there have been a better education. It’s not so much that I learned about the whodunit aspect of crime as much as the importance of whydunit. And that’s the sense I try to bring to every novel. Figuring out a who is certainly a challenge. But delineating a why can be more rewarding.