When Sian O’Callaghan fails to return home after a night out, her mother, Elaine, grows increasingly worried, and DS Steve Fulcher begins a missing person investigation. With few leads to go on, the police and townspeople organize a search party of a nearby forest. Meanwhile, the disappearance strikes a chord with Karen Edwards, the mother of another local girl, Becky, who went missing years ago.

Steve and his team confront the possibility that an officer who committed suicide could be responsible for Sian’s disappearance. But then information emerges that points them towards a new prime suspect: local taxi driver Christopher Halliwell. Fearing that Sian’s life is in imminent danger, Steve pushes for an “urgent interview” with Halliwell, against the advice of his colleagues.

Detective Superintendent Steve Fulcher takes chief suspect Christopher Halliwell to a remote location in the Wiltshire countryside to question him about the whereabouts of missing Swindon girl Sian O'Callaghan.

The remains of two murdered women are recovered due to the actions of DS Steve Fulcher; the families of Sian and Becky soon discover that, despite the confession of Christopher Halliwell, getting justice will not be straightforward.

Karen Edwards refuses to give up her fight to get justice for Becky; DS Steve Fulcher begins to witness the consequences of his actions, after eliciting a confession from Christopher Halliwell.

When Wiltshire Police find a way to bring Christopher Halliwell to court for Becky's murder, Fulcher realizes that he will have to come face to face with the man who ruined his career.