It is 1984 and Gerry Ried is a young and ambitious undercover agent for the MI5. Having infiltrated the IRA, he sets his sights on gaining the trust of Liam, one of the most important and respected men in the organisation. Going against his MI5 handler's advice, he risks becoming compromised by getting further involved in terrorist activities, such as the Brighton bombing which threatens to kill Margaret Thatcher and her cabinet, all to get closer to Liam. Despite the dangers of his identity being revealed, he uses his position as Liam's protégé to warn another British spy whose cover has been blown. It saves the agent's life but from then on, Gerry is convinced that he is being watched and his life could be in danger. He is, however, not yet ready to give up on his career's ambition: to hand Liam over to the British authorities.