British crime novelist Sophie Hannah is on the motorway headed to York, England, the final stop of her U.K. book tour, chatting on her cellphone (no worries, she has a driver) about the genesis of her new psychological thriller, Perfect Little Children (Morrow/HarperCollins, Feb. 4).

In the United States, we’d call it a “soccer mom” moment, even if this particular soccer mom has a string of witty and successful mysteries to her name. 

It all began when Hannah took her son to a football (aka soccer) match outside Cambridge, where her family lives. (And no, “football mum” apparently is not a term in England.) Realizing she was near the new house of an old friend she hadn’t seen in years, Hannah decided to drive by. When her friend drove up, the novelist had a proverbial light bulb moment: What if her friend’s kids were the exact same age they were when Hannah last saw them, 12 years earlier? “I thought, ‘I’ve got to write a book about it!’ ”

Perfect Little Children opens with that chillingly imagined scenario. Beth Leeson is Hannah’s alter ego, and her long lost (and mysteriously estranged) friend is Flora Braid. As Beth watches, a haggard and older Flora emerges from her car with little Thomas and Emily. Flora’s kids should be 17 and 15; instead they appear to be 5 and 3, trapped in time. How can that be?

Part of the appeal of the zippy Perfect Little Children is the contrast between the creepy, secretive Braids and the relatable Leesons—mom Beth, dad Dom, and teenagers Zannah and Ben. They’re a “totally normal family,” as Hannah, 48, puts it. And yes, the writer drew on some folks she knows pretty well. “The two teenagers [Zannah, who becomes her mom’s assistant sleuth, and Ben] are totally based on my kids,” Hannah says. “They were very happy to be put in a book.” Her daughter, Phoebe, is 17 and son, Guy, is 15.

Tenacious Beth, a massage therapist, shares her creator’s DNA, too. “Once I had the idea for Beth seeing the children who appear to be the same age, I thought, ‘What would I do if I saw that?’ Would I think that’s weird, and forget it? No, I’d have to pursue it; I would have no choice.”

That’s the crux of Perfect Little Children for Hannah: “When it becomes a moral duty to interfere in another family’s business. Beth is sure something sinister is going on in the Braid household. I don’t care if people think I am a nosy old bat! You have to know when to interfere and when to mind your own business.” (Hannah suggests her own husband, Dan, might be a bit less tolerant of such homegrown investigations than Dom is.)

Perfect Little Children couldn’t be more modern, with its smartphone obsessed, f-bomb dropping (but likable) teens and provocative questions about “perfect” children and helicopter parenting run amok.

But Hannah also has an impressive side gig that’s steeped in the past: She’s keeping Agatha Christie’s famed Belgian detective, Hercule Poirot, alive with original new mysteries sanctioned by the Christie estate. The Killings at Kingfisher Hill, Hannah’s fourth Poirot tale, is due from Morrow/HarperCollins in August and follows the mustachioed investigator on a murder case that takes him by bus from London to an exclusive estate. “I wanted it to take place on a mode of transport Agatha had never used,” says Hannah, who first fell in love with Christie as a 12-year-old. “She’d used trains, planes, and boats, but a luxury passenger coach she hadn’t done.”

After four books, is Poirot becoming her own character? “[Christie] will always have ownership,” says a humble Hannah. “I feel it’s my job to remind people of how brilliant he is.”

Hannah, who also writes the popular contemporary Zailer and Waterhouse series featuring a pair of married cops, enjoys toggling between time periods. The forensic modes of detection may have changed in a century, but one thing remains constant, she says: “the human side.”

Further flashing her versatility, Hannah, who started as a poet, surprised her crime fiction fans in 2018 when she wrote a sassy self-help book, How to Hold a Grudge. That led to a podcast, where Hannah and guests muse over the “transformative” power of grudges. Does the grudge expert think Brits should hold one against Prince Harry and wife Meghan for absconding to Canada?

No, but she says people in the U.K., like many Americans, have been abuzz,  speculating about possible motives behind the couple’s shocking “Megxit.” “I’ve literally got no idea what went down,” she says. “I’m surprised so many people think they do know, because I haven’t got a clue.” Could she perhaps solve the mystery in her next thriller? Hannah laughs and seems game. “I’ll try to give it a cameo role.”

Jocelyn McClurg, former books editor at USA TODAY, is a freelance writer in New York.