In Giles’s The Boy at the Keyhole (Hanover Square, Sept.), a psychological thriller, a vulnerable child faces off against an imposing housekeeper in a decaying mansion.

You have previously written children’s books (the Ivy Pocket series). What do you find is the main difference in writing for children and writing for adults?

My children’s books are humorous adventures, and that informs the way I fashion the narrative voice—light and whimsical. With this book, the tone is much darker, and the challenge was to tell a very adult story through the prism of this boy’s naive and fragile worldview.

This novel could be described as the equivalent to a theatrical two-hander. Did you ever think about your book in this way as you were writing the story?

I was very aware that the story is, in essence, two characters alone in a vast and crumbling house. That was the appeal and the challenge. In terms of its theatrical potential, it definitely occurred to me and I think somewhere in my imagination it’s already been staged. Off-Off-Broadway, but there were three curtain calls.

The housekeeper in the novel is reminiscent of Mrs. Danvers in Daphne du Maurier’s Rebecca. Why do English housekeepers make for such good villains?

The fictional English housekeeper is a towering figure who, though a servant, wields great authority and power. English housekeepers are always stern and dignified, adept at withering glances and very likely have a set of keys hanging from their belt, one of which almost certainly unlocks a room up in the attic where no one can hear you scream.

There are so many great novels that deal with children confronting adult evil. Do you have any favorites?

Uncle Silas by J. Sheridan Le Fanu is one of those books I reread every year. Though Maud is a teenager, not a child, Le Fanu creates an atmosphere of pure dread around her—she is at the mercy of dark forces plotting to bring her down. That atmosphere of sinister potential was definitely an inspiration when writing my book.

Your novel needs to take place in a period before cell phones and the internet. Do you think this technology makes writing a thriller or mystery novel more difficult today?

Absolutely. My novel depicts a mother and son separated by the Atlantic Ocean and requires a legitimate and believable absence of communication.

You’ve placed your protagonist in a frightening situation. What scares you?

I think that space between perception and truth is terrifying because that’s where some of the worst crimes we commit against each other are justified or made righteous.