THEIR LITTLE SECRET

DI Tom Thorne (The Killing Habit, 2018, etc.) is convinced that a woman who threw herself under a train at the Highgate station wasn’t a routine suicide. He’s absolutely right, but not at all for the reasons he thinks.

Mary Fulton knows perfectly well why her sister, university lecturer Philippa Goodwin, killed herself: Because she’d been fleeced, dumped, and ghosted by Patrick Jennings, who’d bilked her out of 75,000 pounds before he took his departure from her life and her cellphone records. While he’s waiting to see if Jennings has any record of having done this before, as he surely must have done, or has left any traces the Met can follow up, Thorne is pulled into another case: the murder of 17-year-old Kevin Deane on Margate Beach. The surveillance cameras that have redefined the turf of contemporary British mysteries indicate that Kevin was bashed to death very shortly after he had sex with a woman who’s vanished as completely as Patrick Jennings. In fact, as Billingham reveals at a moment guaranteed to catch the savviest readers off guard, the two fugitives have found each other and are locked in a larcenous folie à deux bound to claim more victims, including perhaps each other. The development of their unholy union, which has more layers than an onion, is so compelling that it shunts Thorne and his mates to supporting roles and virtually guarantees an anticlimactic ending. But Billingham, sweating both logistical and psychological details, creates a deepening sense of nightmarish surrealism along the way until Thorne has to acknowledge that “there was very little about this case that wasn’t weird.”

An object lesson in how to take an established series into shockingly deep waters without losing the thread that keeps the franchise going. The detection that normally drives each entry is the least of this one’s dark appeal.