Catherine Cawood is a policewoman in the sarcastically nicknamed Happy Valley; the drug-affected Calder Valley in West Yorkshire, England. Her private life is complicated. She still sees and sleeps with her ex-husband, journalist Richard Cawood, even though he has a new woman in his life. She lives with her sister Clare, a recovering addict, and grandson, Ryan, whose mother, Catherine's daughter, Becky, killed herself after being raped. Now the man Catherine believes to be the rapist, Tommy Lee Royce, is out of jail and back in town. At the same time, Kevin Weatherill, disgruntled that his boss Nevison Gallagher will not give him a raise so he can enroll his daughter into a good school, conspires with caravan park owner Ashley Cowgill and his employees, Lewis and Royce, to kidnap Nevison's adult daughter, Ann, for a ransom. When Nevison has a change of heart and offers to pay for both his daughters' tuition, Kevin wants to abort the operation but the others go ahead with it. As the kidnapping unfolds, more people are drawn into the investigation and conspiracy, leading to tragic results.

Following Catherine's visit to the house Royce moves Ann but the van in which he and Lewis are taking her is stopped for speeding by policewoman Kirsten McAskill and so Royce, to Lewis's horror, runs Kirsten over, killing her. Reminded of her daughter's death and accused by Kirsten's partner of pushing her into action Catherine is devastated and, whilst Richard offers to accept Ryan, she can do without being told not to prosecute Gascoigne for drink and drugs as he donates to the police fund. Cowgill is also appalled by Royce's actions, particularly as Royce wants to kill Ann to stop her talking but gives Nevison some hope by suggesting Ann will be released after another ransom payment delivered by Kevin. As a result Helen, who wanted to speak to Catherine, tells her she has changed her mind. Delivering the money to Cowgill Kevin is shocked when Lewis tells him that Royce killed the policewoman whilst Catherine decides to investigate the house where Royce was seen and is suspicious of what she finds in the cellar.