Each season of the great British series “Happy Valley” begins the same way, with the rock-solid cop Catherine Cawood (Sarah Lancashire) facing the everyday bizarrerie of policing in a tired, depressed, grimly beautiful pocket of West Yorkshire: teenage sheep rustlers, a jilted boyfriend threatening to set himself on fire, unseen agitators heaving kitchen appliances out of upper-story windows onto patrol cars. Compassionate but impatient and prone to anger, smarter than the detectives who condescend to her, Cawood wears her black uniform and neon vest like a bulky suit of armor. She’s a contemporary knight errant, upholding a code of decency against the terrors of modern life.
“Happy Valley,” whose final season premieres on Monday (streaming on Acorn TV and AMC+, broadcast on BBC America), is a pocket-size, prosaic saga — a hero’s tale contained in three six-episode seasons and embedded in a family drama. The emotions that buffet the characters are epic in scale, but the action, though it has occasional flashes of brutal violence, tends to be of the everyday, walking-and-talking variety. Like all mythical heroes, Cawood has an antagonist, the psychopathic rapist and killer Tommy Lee Royce (James Norton), who is the father of her grandson. But for long stretches of the show, he is in prison, and he and Cawood spend much more time stewing about each other than actually facing off.
The second season was shown in 2016, and that seven-year gap is reflected onscreen. Season 3 begins with Cawood counting the days to her retirement and enjoying atypically peaceful relations with her sister, the recovering alcoholic Clare (Siobhan Finneran), and with her now teenage grandson, Ryan (Rhys Connah). The center quickly fails to hold, however, as both the emergence of a body in a drained reservoir and Cawood’s discovery of a profound betrayal by someone close to her raise the specter of Royce, even though he is in prison for life.
In its structure, “Happy Valley” is very much a traditional British crime series, with seemingly unconnected plot strands and investigations that wind themselves together against a backdrop of cop-shop politics. But in the hands of the accomplished writer and producer Sally Wainwright (“Gentleman Jack,” “Scott & Bailey), who has written every episode, it is also a powerful social drama that focuses unflinchingly on male violence against women without sliding into speechmaking or heavy-handed symbolism. In the new season’s major subplot, a less-than-sympathetic female character is caught between two seemingly more capable men whose weaknesses run deeper than hers.