When Orla Payne was seven years old, her brother Callum mysteriously vanished. There were no clear leads about his disappearance. The case was eventually dismissed, as the police concluded their uncle killed himself out of guilt over murdering Callum, despite a body never being found. Twenty years later, Orla is still haunted by the tragedy and remains convinced of her uncle's innocence. Orla gets to know historian Daniel Kind and it is he who recommends she contact DCI Hannah Scarlett, head of the Cold Case Review Team. When Orla is found dead, Hannah discovers that investigating the past can throw up some very dangerous truths indeed.