The early 1980s. Belfast. Sean Duffy, a conflicted Catholic cop in the Protestant RUC is recruited by MI5 to hunt down Dermot McCann, an IRA master bomber who has made a daring escape from the notorious Maze Prison. In the course of his investigations, Duffy discovers a woman who may hold the key to Dermot's whereabouts; she herself wants justice for her daughter who died under mysterious circumstances in a pub locked from the inside. Duffy knows that if he can crack the "locked room mystery," the bigger mystery of Dermot's location might be revealed to him as a reward. Meanwhile, the clock is ticking down to the Conservative Party Conference in Brighton in 1984, where Mrs. Thatcher is due to give a keynote speech."