In British author Michael Marshall’s latest thriller, The Intruders (Reviews, June 4), Jack Whalen, an ex-LAPD cop, is pursuing a new career as a writer in Oregon when some strange happenings start to undermine his pursuit of the American dream.

Did you start with a central theme or idea for The Intruders?

I was intrigued by the dualisms that seem manifest within us, our wants and needs and desires, the unknowability of other people and, to an extent, ourselves.

“Intruders” takes on various meanings throughout the book.

The further I kept exploring, the more I found meanings of “intruders” layering themselves within the novel. The protagonist, Jack Whalen, has written a nonfiction book about crimes of intrusion. There’s also the intrusion which takes place when the noncriminal insinuate themselves into the lives of others, especially emotionally. The word also operates in relation to the early colonization of America, and finally, of course, relates to the group of people into whose story Jack gradually finds himself drawn.

Numerology plays a big part in the book. Did you have to do a lot of research on the subject?

It’s a classic example of something that tends to happen to me when I’m writing a novel. I get very, very interested in something that’s of no relevance whatsoever. I got fascinated by the number nine about six years ago while writing one book or another, and spent a while immersing myself in some odd byways of mathematics, but it took until The Intruders before it suddenly revealed itself as relevant.

Jack Whalen’s seemingly got it all, yet he feels a void.

And don’t we all? Again, I think this is partly due to this dualism which so many of us feel: the sense that though many of our needs seem to have been met, it’s a feeling of lack, of a desire for the other, that often drives our lives. The cultures which, for reasons bad or good, most celebrate a national sense of identity or a shared dream of mythic proportions are the ones which run the greatest risk of having some of their citizens noticing that despite everything, they don’t feel the way they’re supposed to. That they feel like crap, in fact—for which someone, somewhere, must be to blame.

Have the films rights been sold?

The book has just been optioned by the BBC, for development into a TV series. I’m currently engaged upon adapting the novel as a feature-length pilot and establishing ideas and story arcs for the series after that.