It's 1969. Five years ago, teenager Alexandra Tozer was murdered. Her sister, Helen Tozer, will never forget. Returning home after quitting the Met Police, she brings with her the recovering Detective Sergeant Cathal Breen, who slowly becomes possessed by the unsolved case. But Breen is on a trail, for the two men connected to this case met in Kenya, during the Mau Mau uprising; and the history that Britain has turned its face from is now returning to haunt it.

Marylebone, November 1968. Detective Sergeant Breen has a death threat and two burned bodies on his hands. One is an un-mourned vagrant; the other the son of a politician. One case suffers the apathy of the police; the other obstructed by a PR-conscious father. Then the potential perpetrator of his death threats is murdered. Banished from a corrupt system, Breen is finally forced to fight fire with fire.

London, October 1968. As Beatles fans encamp outside Abbey Road Studios up the road, the Marylebone CID is as much an old boys' club as it ever was: comfortably sexist, racially prejudiced and crawling with corruption. Detective Sergeant Cathal Breen is the pariah of the office, having just run out on a fellow officer held at knifepoint, when it's shaken up by the arrival of WPC Helen Tozer: awkward chatterbox, farmgirl, and the first woman to enter the murder unit - apart from the secretary.

Police Sergeant William South has a reason for not wanting to be on the murder investigation. He is a murderer himself. But the victim was his only friend - like him, a passionate birdwatcher. South is warily partnered with the strong-willed Detective Sergeant Alexandra Cupidi, newly recruited to the Kent coast from London. Together they find the body, violently beaten, forced inside a wooden chest. Only rage could kill a man like this. South knows it.

An unidentified cadaver is found in a freezer in an unoccupied luxury house. No-one seems to know or care who it is or who placed it there. When DS Alexandra Cupidi is handed the case, she can have no idea it will lead her to a series of murderous cover-ups and buried secrets. Namely the discovery of the skeleton of public-school boy, Trevor Wood, beneath a housing development. 

When Harry Falcon, a wealthy boatyard owner and decorated World War Two veteran, is found drowned in his bath, DI John Tanner and DC Jenny Evans start by questioning his two sons, each with a motive for wanting him dead. But when the elder son is found with his head smashed in under a toppled yacht, and the younger son has been talking to a local property developer, one who’d spent months trying to buy the yard from his father, the investigation soon leads them towards a dark and dangerous secret, one which nobody can quite believe.

When a body is discovered, bled dry on a beach, the sleepy seaside town of Weston-super-Mare wakes up to a nightmare. For Detective Inspector Louise Blackwell, recently transferred to the town she last saw as a child, it’s her first case on the job. The victim - Veronica Lloyd, an elderly volunteer at a local church - has puncture wounds to her hands. When a priest is found killed in a nearby church in a similarly grisly condition, it becomes clear that Blackwell is dealing with a righteous and bloody murderer. But the victims aren’t random.

In North Devon, where the rivers Taw and Torridge converge and run into the sea, Detective Matthew Venn stands outside the church as his father's funeral takes place. The day Matthew turned his back on the strict evangelical community in which he grew up, he lost his family, too. Now he's back, not just to mourn his father at a distance but to take charge of his first major case in the Two Rivers region, a complex place not quite as idyllic as tourists suppose.

She always went to far. DS Alexandra Cupidi has done it again. She should have learnt to keep her big mouth shut after the scandal that sent her packing - resentful teenager in tow - from the London Met to the lonely Kent coastline. Murder is different here, among the fens and stark beaches. She was the one who found the killers. The man drowned in the slurry pit had been herded there like an animal. He was North African, like many of the fruit pickers that work the fields. The more Cupidi discovers, the more she wants to ask - but these people are suspicious of questions. 

When the body of an old man is found lying in the ruins of St Benet’s Abbey, his throat cut, a knife resting in his open hand, DI John Tanner and DC Jenny Evans are given no choice but to accept a ruling of death by misadventure. But when the body goes missing from its tomb, after a priest is found nailed to a cross, and another impaled on a stake, everything begins to point back to the murder of a teenage girl, thrown from the top of a church tower, some 43 years before.