The team is called to a drive-by shooting outside a London nightclub. They arrive to a scene of carnage with several people dead, or dying.

With the murder of the club manager, the pathologists also determine that the club owner shot his own girlfriend, likely by accident. They also identify an unlikely suspect in the shooting of the club manager. Harry and Nikki confront Leo over his abusive and unprofessional behavior.

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.