Sam Ryan assists the police in the investigation of a multi-vehicle collision that results in the death of 11 people. She is joined by two new colleagues: Dr. Leo Dalton, an experienced pathologist from Sheffield and Dr. Harry Cunningham. As they try to determine the causes of the accident, they find a severed arm that does not belong to any of the victims. They also have to deal with DCI Carol Deacon whose role in the investigation is not quite clear to them. Sam and Leo have somewhat different approaches to their job, particularly in how they deal with the police. Harry performs his first autopsy on a child.

The mystery of the severed arm is partly solved when the police discover a body floating in the river with a missing arm. The pathologists continue their investigation with little help from the police and DCI Deacon in particular. When she reveals to Tom that two of the men in the accident were undercover policemen, he realizes that Sam was correct and that he is being manipulated. The police refuse to tell them what is going on and Sam's interference has serious consequences. Harry continues to try and find a balance between detachment and compassion as one of the survivors of the crash seeks his assistance.

Pub landlord Roly Henderson is accused of stabbing to death his wife Joanne in her sleep and cutting off her little finger. DI Kate Warren is anxious to convict,under pressure from her father a deputy chief constable,to further her career but Clarissa and Nikki find proof of Roly's innocence and his little daughter Emma recalls seeing a strange man in the pub. Nikki visits Simon Marshall,convicted of killing his wife Eleanor four years earlier as her finger was also chopped off after death. Simon tells Nikki his wife was murdered by a biker and Nikki and Jack find evidence to support his story. Nikki believes this man killed Joanne,Eleanor and a third victim,Imogen Lane,who married the older policeman Alan who rescued her from her pimp when she was a teen-aged prostitute. Alan was convicted of his wife's death but is now released. Imogen's mother Edith hated Alaan,believing he killed her husband as well as her daughter,whom she feared he would harm. Edith is unaware that she is being shadowed by Janice Masters,a single parent who also has a little finger missing.

Jack discovers that Kate,under pressure from her corrupt father,has tampered with evidence to incriminate Roly Henderson and demands she accept Nikki's opinion that Alan Lane killed all three victims. They visit Anne Percival,the retired officer who sent lane down even though Imogen's body was never found - in the event because,thanks to Anne,she was given a new identity as Janice Masters. Nikki finds out that Lane has killed nine women who all has histories of domestic turbulence so that their husbands were blamed. After Anne has fatally tried searching Lane's house the team must stop him before he can get to Janice.

Examining Kevin's corpse Nikki is puzzled by stun marks on the body and the fact that Jackie had set up a camera in his room. Thomas is also curious regarding two other mysterious deaths, one at Kingscote Bows, the other at the Pleasant Manor care home, where both were regularly visited by Dr Kahari. When Serena goes missing and Tilly is found dead after threatening to expose Flannery Clarissa books herself into Pleasant Manor to investigate herself,. She unmasks the killers but needs to be rescued by Jack when she puts herself I danger.