Baltimore police receive an urgent call out to Glendale High after gunshots are heard coming from a locked girls' toilet. It appears that three girls are in there but only one, Josie, is conscious. She assures the police through the locked door that she's not the shooter. She also insists that she cannot manage to unlock the door because of the injury she has suffered to her leg.

After a janitor is summoned, the police cautiously enter the bathroom. They find three victims - Josie, whose leg wound seems relatively superficial; Perri, who is unconscious from a bullet wound that has ripped through her jaw; and Katrina, who is dead, shot in the chest.

The investigating team is led by Detective Harold Lenhardt - himself the father of an adolescent girl. He soon discovers information that is at odds with the story Josie is telling. Other clues at the scene suggest there was a fourth girl who witnessed the entire episode from behind a locked stall. Where is she now? How did she get out?

Five years before this fatal shooting in the locked toilet, three girls met aged ten, and took a vow of eternal friendship. How did that passionate friendship change and evolve and finally fall apart? Here Laura Lippman combines police procedural with an intensely human, sad, eternal tale of growing up. As ever, she ratchets up the suspense as she unfolds her story with grace, sympathy and acute intelligence.