After a car accident causing the death of a cop, detective Peter Diamond is assigned to look into the case. Diamond discovers that a civilian on a motorized tricycle was involved in the crash and has been lying on the side of the road for hours. He begins a private inquiry of the victim that leads to a trail of uninvestigated deaths, and realizes that he may have saved the life of a serial killer.
In a Sussex town on the south coast of England, a widely disliked art teacher at a posh private girls’ school disappears without explanation. Meanwhile, a Sussex detective has been suspended for failing to link DNA evidence of a relative to a seven-year-old murder case. When detective Peter Diamond realizes that the suspended officer is an old friend who is not known to make such mistakes, he begins to notice unsettling connections between the cold case and the missing art teacher. Could the two mysteries be connected?