Catherine Cawood is the police sergeant in the West Yorkshire community of Calder Valley, also known as Happy Valley for its high incidence of drug-related problems. She has faced tragedy in her life, namely the death of her daughter, Becky, who took her own life after giving birth to a son. Catherine believes Tommy Lee Royce, who has been serving time in prison for drug-related crimes, is responsible for the events that led to Becky's death. So when she learns that Tommy Lee has recently been released from prison, she makes it her mission to find him. Little does she know, however, that he is now a key figure in the kidnapping of Ann Gallagher, the daughter of a local millionaire, who she is trying to locate as a way to avenge her own daughter's death.