When a former IRA man is abducted, DCI Tom Brannick is forced to confront an assassin who haunts his past, in order to crack the investigation in the present.

Tom continues to search for Pat Keenan's kidnapper, hoping they will lead him to Goliath. But is somebody leading him down a false trail?

Tom and Niamh launch a manhunt for Adam Corry, who has disappeared in mysterious circumstances. Tori Matthews agrees to help Tom in the quest to identify the notorious assassin Goliath, who appears to be at large once again. As pressure builds on the police, Tom must confront the possibility Goliath may be one of his fellow officers.

Tom Brannick enlists the help of Heather Pentland to find out what Jackie Twomey knows about Goliath. Tori Matthews and Tom's daughter Izzy put pressure on Tom to get to the truth. With lives on the line, Tom must unmask Goliath before it's too late.