Sam and Leo arrive on the scene of an accident, involving six vehicles. They begin to investigate the causes of the crash and attempt to identify all the bodies. Sam is called to where a girl's body has been found in the Thames, and finds that there is a connection.

Sam is called upon to investigate the murders of a ruthless businessman and his family, but still finds time for romance when the grisly case reunites her with an old flame. Meanwhile, a preoccupied Leo unwittingly puts his reputation on the line by dismissing a junior pathologist's doubts concerning the seemingly routine death of an elderly woman.

When a truck driver accidentally reverses into a wall, he finds a body there and contacts the police. They phone for Sam, who is currently dealing with a break-in at the toxicology lab, and when she arrives at the scene she examines the body, which is around seven years old. They soon discover that he was murdered and begin to look for his killer.

A young man is found bound at his neck, wrists and ankles in the same location and in similar circumstances to a case Leo worked on. It is apparent that the cases are both linked, and they begin to look into the murders and find their killer.