Belfast hood Martin (Jim Sturgess) is recruited by a British agent (Ben Kingsley) to infiltrate the IRA during the height of the Northern Irish conflict and quickly becomes embroiled in a dangerous game that could cost him his life if his secret is found out. As other informers are brutally murdered, Martin starts to look for a way out, but his handler urges him to stay undercover in this taut political thriller based on a true story.