Creegan races against time to find three recently abducted young boys. Despite Taylor’s reservations, he zeroes in on a suspect who leaves a distinctive calling card at the scenes of the crime. But when the man appears likely to walk free, Creegan decides to take matters into his own hands.

Although Hinks is released Creegan is convinced of his guilt and arranges another interview wherein he gives Hinks a nose-bleed. He uses the tissue that was used to clean up the blood and shows it to Hinks' dog,who then leads him to an abandoned building and the three boys abducted by Hinks. Creegan goes to Hinks' house to kill him but on arrival gets a surprise.

The death of three hospital patients in one night from drug overdoses suggests euthanasia. But these are not simply mercy killings. Drawing from his own near-death experience, Creegan focuses on a murderer with whom he shares a surprising commonality.

The investigation's attention turns towards locum Julie Carney following the attack on Creegan. When she commits another murder in Wales, Creegan realises that he needs to set a trap to lure her home. Rivers and Krietman's pursuit of an unstable Carl Burgess results in Burgess trying to kill a patient, and then electrocuting himself, from which he dies of his injuries. When Julie Carney resurfaces, Creegan is forced to watch on as she tries to commit suicide.

Someone is stabbing horses as part of a worldwide, Internet-based crime ring. As the police close in on those responsible, the drug-fueled attacks escalate to human mutilation and murder. Believing these are copycat killings, Creegan visits an unorthodox source to lure out the mastermind behind them.

A serial killer, before murdering and scalping young women, sends an email to journalist David Laney. The OSC Unit gets Laney on board and is able to arrest a man named Emerson before he goes for a kill.