Eighteen months have elapsed. While investigating a bizarre case of sheep-rustling, Catherine discovers the corpse of prostitute Lynne Dewhurst, Royce's mother, whom she had warned to keep away from her grandson. Along with new recruit Ann Gallagher, Catherine joins the investigation. The woman has been killed and sexually assaulted. CID officer John Wadsworth, meanwhile, is more concerned with preventing his mistress, Vicky Fleming, from telling his wife Amanda about their affair, whilst Ann's father Nevison has to sack volatile employee Sean Balmforth, and Clare meets an old flame, Neil Ackroyd. Royce is given consolation in prison by besotted visitor Frances Drummond, to whom he suggests that Catherine killed his mother.

Catherine brings home Croatian Ilinka, one of several women rescued from human traffickers, and places her with elderly Polish friend Winnie before joining the house-to-house investigation of the serial killer who murdered three female victims. After his wife's death, Nevison reinstates Sean but Catherine suspects the young man of stalking prostitutes. She also attends Lynn's funeral, which Royce has been allowed to attend. He makes a scene and accuses her of killing his mother, a fact which does not please her superiors. Also present is Frances Drummond who, under an assumed name, has started teaching at Catherine's grandson Ryan's school. Returning home, Catherine argues with her sister, who has started drinking again, whilst John's attempt to end his affair with Vicky does not end well.

Catherine reconciles with Clare but her superiors see her as unstable and offer medical leave, which she rejects - accepting to see a therapist instead. Vicky's body is discovered but the murder of yet another prostitute allows John to suggest that both were the serial killer's victims. His marriage is on the rocks anyway. Catherine is shaken by the apparent suicide of one of Ilinka's slave-masters, whom she had tasered and arrested but who had been released on bail. Ilinka thinks he has been silenced. Meanwhile, deceived by Royce's lies, vulnerable, besotted Frances Drummond is encouraged to ruin Catherine's life.

Catherine and Ann have a long drunken night out while Frances makes the petrol bomb she plans to throw through Catherine's window.

Catherine learns of a painful betrayal close to home, and Faisal comes under increasing pressure from all sides.

Catherine confronts Clare and presents Ryan with an ultimatum. Faisal and Joanna hatch a plan that takes an unexpected turn.

As Tommy's big day approaches, Catherine becomes suspicious, and Ryan finds a new way to defy her.

Catherine races to protect her family following Tommy's escape. A murder investigation begins.

Scores are settled for good on Catherine's final shift, and Ryan faces a moral dilemma.