When allegations of undue force threaten her career, DI Fia Lucey is sent back to her hometown of Blackwater to investigate a missing person case; while there, Fia must also confront the dark secrets of her family's traumatic past.

With the case now confirmed to be a murder, Fia suspects her new partner, Detective Cian Furlong, may have played a role in Roisin Hurley's death; after Cian's confession, Fia cautiously accepts his help with the investigation.

With the victim's daughter, Carrie, missing, Fia races against time to uncover the truth behind the murder; a press conference erupts with allegations, and old wounds are reopened as the anniversary of Fia's family tragedy approaches.

As the past and present begin to merge, the truth behind the abuse of several young women is exposed; the discovery of a body that's been in the lake for over twenty years points to the most powerful man in town and a sinister collusion.