Jack leads an investigation into the dark world of child sex offenders. He becomes too emotionally involved within the case after a brutal attack is made on an amateur paedophile hunter Scott Freeman.

In the first of a two-part story, DI Martha Bellamy's neighbour, barrister Jonathan Moxton, is discovered at his home with serious head injuries, his wrists bound with a belt and a pair of knickers stuffed in his mouth. DS Jack Weston guesses he was involved in a sex game that went badly wrong and suspicion falls on Saul Hammond, the man who found him.

The suspected leader of the paedophile ring is murdered and the hunt is on to find the killer.

The body of a student, Michael Collins is found on Crowford common. The killer is suspected to be the person who attacked Moxton.