Happy Valley is a dark, funny, multi-layered thriller revolving around the personal and professional life of Catherine, a dedicated, experienced, hard-working copper. She is also a bereaved mother who looks after her orphaned grandchild.
Eighteen months have passed, and Catherine is spinning plates at work and at home, where Ryan approaches his tenth birthday. Tommy, serving a life sentence in a high-security prison, finds a way of keeping a watchful eye over Ryan from behind bars, while Catherine becomes a murder suspect after finding a dead body.
Catherine arrives home with Ilinka, an emaciated Croatian woman who has been rescued after being trafficked and enslaved for the past four years. Meanwhile, John's panic over Vicky's threat spills out into his home life.
Tommy urges Frances to go further with her attempts at making Catherine's life a misery, and a therapist tries to understand why Catherine attended Tommy Lee Royce's mother's funeral. Meanwhile, John begins to sweat when a new body is discovered.
Sean becomes prime suspect when Leonie is raped, and the authorities believe he could be responsible for the string of murders Andy and the team have been investigating. Meanwhile, John has to think fast when he's asked why his number was on Vicky's phone, and a gift for Ryan on his tenth birthday reminds Catherine that danger may be closer than she thinks. Elsewhere, Daryl takes action when he is confronted by the three lads who have been bullying him.
Daniel suspects somebody at school might be responsible for Ryan's new-found interest in Tommy, and tries to explain that he wasn't really a dad to him, while, despite Sean protesting his innocence, Jodie and John receive permission to charge him with all of the murders. However, delight at the developments is tempered when another body is found in the early hours, and Daryl wakes a stunned Alison in the middle of the night and confesses to murder, leading to dramatic scenes at the breakfast table.
Catherine and Shaf call in at Far Sunderland farm to visit Alison and Daryl, but discover a scene of carnage when they enter the building, with Alison slumped on the dining table covered in blood having taken an overdose. Meanwhile, Andy and Jodie begin to suspect that the person who killed Vicky Fleming could be someone on the team and as the investigation heads towards a conclusion, John's torment increases, leading him to take drastic measures to avoid the consequences of his actions.