The life of DI Cadi John and the lives of those around her are forever changed by the discovery of the body of a young woman, Mali Pryce, in a river. Mali has been missing since 2011 and the police question where she has been held for all this time. Will the person responsible for Mali's death strike again? The pressure is on for the North Wales police force to find some answers quickly.

Cadi and Owen investigate a possible link to another girl who disappeared. Megan hides her difficulties from friends and family. Dylan takes an interest in Lowri.

The police investigation enters a new phase when DI Cadi John and DS Owen Vaughan are called to the scene of a potential kidnapping in the middle of the night. Their concerns that a serial kidnapper is on the loose are confirmed.

Dylan and Iona clash regarding Megan. Mari and Ryan continue the questioning procedure, but Mari deviates from protocol.

Cadi and Owen discover a possible connection to an old case, which Cadi's father investigated. Lowri tries to return to her normal routine.

Cadi questions Endaf in prison about the murder he was convicted for. Owen reviews the older case files and receives a new missing persons report. Iona visits Megan.