'Girl A' was convicted of murdering three people when she was a child. Now she's missing and a man is dead. The clock is ticking for Scottish detective DCI Christine Caplan to bring her to justice - but the truth may be darker than even she fears . When a body is discovered in the water at Connel Bridge, the police assume it's an open-and-shut case of suicide. But when DCI Christine Caplan is called in to take a closer look, she discovers that darker truths lurk beneath the surface, and suspicion begins to turn to a young woman recently out of care. Known only as Girl A, her identity remains anonymous, protected under law. Her violent past includes an allegation of the murder of a younger sibling, so the timing of this new death seems too coincidental. Then a vigilante sets her home on fire and she flees, so the 'child killer' is now on the loose - and at risk herself.

As Caplan launches a search for the elusive teenager, looking for connections between her and the dead man, she turns to Girl A's past for answers. And when she gets them, she realizes the truth may be even more sinister.