In 1993 Belfast, Colette lives with her mother and brothers. In the opening scene, set twenty years earlier, the Troubles results in the death of her younger brother when they are children. This presumably motivates her in later life. After a failed attack in London, Colette is arrested and offered a choice: either she spends 25 years in jail, thus losing everything she loves including her young son, or she becomes an informant for MI5, spying on her own family. Colette agrees to do so. An MI5 officer, Mac, is assigned as her handler. In return Mac offers a new identity to her after a period working for MI5. Soon Mac learns that his superior Kate Fletcher is using Colette to protect her mole (espionage) inside the Irish organization. Mac tries to find the identity of the informer and protect Colette.