聚焦活跃在1970年代的美国连环杀手、强奸犯——“金州杀手”。他犯下至少50起入室强奸、13起谋杀，一直隐藏在黑暗中。2018年，前警察Joseph James DeAngelo被起诉，疑为这名杀手。剧名来自金州杀手威胁一名受害者的话：“你将永远开不了口，而我将消失在黑暗中。”
　　本剧改编自作家Michelle McNamara对金州杀手的同名纪实调查书。

　　A private jet crashes into woodland outside London. Among the passengers is a former U.S. Ambassador. Thomas investigates the apparent suicide of a successful businessman, finding unexpected connections to the plane crash.

　　Nikki and the Lyell unit are called in to investigate an ysgou.cc attack against a transgender man.

　　Thomas and Jack are surprised to see Nikki back at The Lyell, the disappearance of her friend Sally forces her to face her back after her harrowing experience in Mexico.

　　As Leo's replacement Thomas Chamberlain arrives Nikki investigates the murders of Rachel Freedman, shot in the head, and her little autistic son Nathan, who was poisoned. Nikki rejects policewoman Anne Burchett's theory that Rachel killed them both but is perturbed when an impostor, claiming to be Rachel's sister, visits the morgue. At the same time the disfigured corpse of Eva Liron is discovered, killed with the same poison as Nathan. She had been the nanny to French hot shot footballer Isaac Dreyfus and was planning to blackmail him over a sex tape of them both. Jewish Isaac is a controversial figure due to his anti-Muslim sentiments but he denies ant part in the murders. Then another victim, Isaac's agent Mousa, is discovered dead.

　　Following a court appearance for drunk driving, Leo is required to perform unpaid work as a punishment, assisting AJ, a community worker on a run-down,largely black-occupied housing estate in South London. AJ is hoping to divert boys away from crime by encouraging them to do sports, and, though initially dismissive of Leo as a white intruder, comes to respect him after he has saved the life of Errol, a former gang member now anxious to keep his little brother Levi out of trouble. Errol has been stabbed in the leg by members of a gang from a rival estate and Leo stops him from bleeding to death. Earlier in the week a young girl called Shana Block was stabbed to death at a funfair and her murder recorded on a mobile phone. As Shana lived on the estate police sergeant Wallace involves Leo as a go-between with the suspicious residents. Also on the scene are Harry and Nikki, the latter dating Ryan, a young Scottish paramedic she met when called to the scene of Shana's death.

　　The pathologists investigate when a military helicopter crashes into a refugee detention center. Harry and Nikki actually witnessed the crash and were first on the scene but the case is complex since the center was Ministry of Defense property leased to the Home Office. The team is shocked at the conditions they find in the center and Harry, who has a close friend in the RAF, is shaken when a government Minister attributes the accident to pilot error.

　　When a boat carrying illegal passengers is found crashed in the Thames, the team investigate.

　　The team is shocked when Leo Dalton's wife and daughter are killed when a fancy sports car careens out of control and smashes into a café. The police are puzzled by the cause of the crash but believe the driver may have been involved in a identity theft ring when they find several several passports and ID cards in the vehicle. Meanwhile, Nikki must perform urgent autopsies on two bodies found floating in the river.

　　A Time to Heal -The team is called out to Northern Ireland to investigate the bodies of two men killed by paramilitaries twenty years ago. For Sam, it is a case that is soon to turn personal…
　　Death by Water - Tensions are running high in the ‘leaderless’ team as Leo and Harry clash over an investigation into an outbreak of breathing difficulties among children on the South Coast.
　　Nowhere Fast - When members of a race horse owning syndicate are killed in a helicopter crash, Leo and Harry investigate – and an unexpected new face at the mortuary lends a helping hand.
　　Body 21 - Approached by a group of survivors from a recent train crash, the team investigate the wreckage and a new mystery – the identity of the unidentified body 21.

　　Answering Fire - In a suspected terrorist attack on a London hotel a government minister is killed. As Sam and the team investigate the case, old friends and government officials soon muddy the water.
　　Fatal Error - When two brothers are found dead in a police cell, Sam and Leo find themselves on opposing sides of an Old Bailey court case – then a 13-year old murder resurfaces, questioning Sam’s findings…
　　Running on Empty - When a young woman falls to her death, the police believe she took her own life. When Sam, Leo and Harry are called in, their investigations soon unravel a tragic story.
　　Beyond Guilt - As Sam investigates a brutal murder, she is also asked to investigate a professor linked to the case and discovers the case is a lot more complicated than first appearances suggested.

　　一名法医在案件侦破中努力确定自己的角色。