Happy Valley ★★★★½
Friday, 8.30pm on ABC

Sergeant Catherine Cawood has been through the wringer. A single grandmother raising her grandson after her daughter committed suicide, she also has had to assume the responsibility of looking after her sister, a recovering heroin addict who lives with her. Over two series, she’s tracked down serial killers, mobsters and kidnappers, and engaged in a running battle with Tommy Lee Royce, the man who raped her daughter – and fathered her grandson – and whom she holds responsible for her death. Catherine’s come close to death herself at Royce’s hands, and had to deal with her own and others’ tragedies.

As one of television’s most ill-used and traumatised characters, Catherine Cawood could easily have been a caricature of grief and vengeance, ploughing through her endless trials in a chaos of melodrama and catastrophe. Fortunately, the character, as written by series creator Sally Wainwright and portrayed by the peerless Sarah Lancashire, is instead a compelling and complex mix of strength and vulnerability, and at all times both intensely watchable and utterly believable.

The third and final season of Happy Valley picks up seven years after the second, with Catherine nearing retirement and looking forward to hiking the Himalayas and a steep decline in the number of atrocities she has to confront on a daily basis. Sadly, the murky depths of human depravity are not done with Sergeant Cawood, as she quickly realises when human remains are found in a reservoir.

Naturally, the latest gruesome discovery leads yet again to Tommy Royce, who keeps turning up like a very bad penny. Unbeknown to her, however, Royce never really left her life: her now teenage grandson, Ryan, has been in contact with his father in prison, maintaining a relationship with the man who not only raped his mother, but nearly killed his grandmother. The web of violence that unfolds will take in organised crime, domestic abuse, and more than one murder. Catherine will have to pick her way through one more tragic minefield before she can think about her happy Himalayan ending.

From its inception, Happy Valley stood out in the crowded crime drama field, and in its third season it reaches a pinnacle few programs manage. Its triumph is keeping a multi-stranded narrative grounded in a reality that never feels less than credible. Where others stretch to excess and histrionics, Happy Valley keeps its feet on the ground and makes its impact thereby far greater.

The basis for the show’s achievement is, as with all great shows, the writing. Wainwright crafts her world with care and an eye for detail, both in character and plot, that makes the story live and breathe. Though Happy Valley deals at a fundamental level with struggles of good versus evil, there is nothing trite or basic about it. Location is a part of that: set in the Yorkshire Dales, the show bears the earthy, no-nonsense nature that is often associated with that part of the world. Nothing glamorous or racy about Yorkshire, and that flows through to the events playing out.

That brilliant writing, though, is allowed to shine due to the spectacularly good performances. Lancashire has been showered with praise for her portrayal of Catherine Cawood, and rightly so. Warm and caring, dedicated to her job and the hurt and damaged people it brings her in contact with, Cawood seeks truth with a quiet, steely strength, but is no superhero: she has suffered huge trauma herself and carries it with her at all times. The scars of the past mean she doesn’t always make the right decisions, but driven by compassion, she will prevail, even if sadder and more bruised by the end.