Nikki and Harry continue to investigate the death of Penny Harris. Harry is shocked to learn that she had apparently at some point in her life had a child but her husband denies any knowledge of such. Another death in the Harris family allows them to narrow the suspects and identify the killer. Leo continues to look for clues and the police think they have solved the case through fingerprint evidence, but Leo is able to prove that the suspect has been framed. The victims penchant for videotaping his activities provides a vital clue.

Alison Garland is a 14 year old schoolgirl found dead on the school grounds just after lunch. She appears to have slit her wrists and committed suicide, but there is also evidence that she had sexual relations just earlier that day. As Leo Dalton looks into the case he learns that Alison was also a school bully and was a very unhappy young woman. Harry assists the police in the stabbing death of a car dealer. The evidence suggests that he was stabbed in his garage and his body then dumped. The case takes a radical twist when they find that the knife found by Alison's body was also used to kill the car dealer. Nikki assists the police in the death of an elderly woman who appears to have been maltreated.

A third murder is discovered on school grounds and Leo realises the killings are connected to a sinister teenage pact. Meanwhile, Nikki proves her elderly victim died of hypothermia - but there is still a guilty party to be caught.

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.