Thrillers aren't my go-to genre, but there's a certain kind of crime drama—British, psychologically nuanced, helmed by a damaged, sexy P.I.—that never fails to put me in its thrall. Think Kate Atkinson's Case Histories or ITV's Broadchurch (and if you haven't had the pleasure in either case, fix that now). I wasn't expecting this debut to meet my standards, but boy does What She Knew deliver.

The event that sets the story in motion is enough to still any parent's heart: on a walk in the woods near Bristol with his divorced mom, Rachel, 8-year-old Ben Finch begs to run ahead to their favorite rope swing. Rachel nervously agrees because "in the absence of Ben's dad I thought it was my responsibility to…encourage Ben to be independent, to take risks, to discover life." The empty, still-swaying swing she sees when she arrives tells her she made the wrong call.

In the nightmare days that follow, DI James Clemo (sexy, damaged) battles the clock to find Ben. As the odds that Ben has survived diminish, Rachel finds herself questioning not just her own judgment, but everything and everyone. Is her "mother-of-the-year" sister Nicky uncomplicatedly devoted—or hiding devastating secrets? Could her best friend Laura be feeding information to the ravenous press? Is maternal instinct her best friend, or will it invariably lead her astray? Detective Clemo seems devastated by the case on a deeply personal level. But why?

As Rachel's version of events alternates with Detective Clemo's, Gilly Macmillan keeps the tension building—this is an up-til-3-am kind of read—without stinting on substance or character development. Like any violent disruption, Ben's disappearance strips away pretenses and crumbles the facades of those affected. "Are any of our… relationships really based on secure foundations?" Rachel wonders. By the end of this gripping, insightful novel, you'll be wondering that yourself.