A car is pulled from Strangford Lough, the owner kidnapped. DCI Tom Brannick (James Nesbitt) recognises the calling card of a legendary assassin known as Goliath. The legend goes he was a serving police officer who vanished without trace twenty years ago and among his original victims was Tom's wife. Against opposition from old friend DCS Jackie Twomey (Lorcan Cranitch), Brannick and his partner, DS Niamh McGovern (Charlene McKenna) break open the Goliath case in the hope that it will help them solve the kidnapping. As they dig deeper, they find gaps in the original Goliath investigation. Someone tried to suppress the truth. When a vital clue leads them out to an island on Strangford Lough, a discovery is made that changes everything.

DCI Tom Brannick (James Nesbitt) continues the hunt for legendary assassin, "Goliath". Protocol will not let Tom near the island investigation. Driven by his hunger to settle a score with the past, Tom attempts to solve the kidnapping case. With the help of Birdy (Chris Walley), they are soon in perilous pursuit of a possible connection to the crime. But the question soon arises: Is it Goliath they hunt or someone making a false trail? There is jeopardy for Tom and his daughter. There is truth in the mouth of Adam Cory (Ian McElhinney), relative to another victim of Goliath. Tom must piece it all together before it is too late.