Belfast. The recent past. An old drunk, Sean, sees a couple kiss then part. Two masked men follow the woman into a block of flats and drag her away. She drops a scrap of paper, which is picked up by Sean.

The present day, the Maze prison. Con Ellis is one of a group of prisoners given 24-hour leave. Also on release are loyalist gang boss Geordie and IRA chief Thomas Macken. Con dreams of his former lover, Layla, and determines to find those responsible for her recent death.

On his release day, Con is met at the prison by his father and cousin. He goes home to a family party but he and his cousin leave to get hold of a gun. In a supermarket, they meet a maverick IRA man, Marty, who supplies the weapon and tells Con that Layla had been seeing another gunman, Alex, shortly before her death. Marty suggests Con should just kill any Protestant drinking at the local UFF pub, The Bluebell, in revenge. Back in their car, Con and his cousin are jumped by hoods, who take Con's gun and his 24-hour prison pass.

Con goes to the University library where Layla had been working. He meets her French colleague, Sophie, who gives him a lift to Sinn Fein's offices to find Thomas. They see Thomas address a meeting, where his calls for a ceasefire and talks are bitterly rejected by rival Rory McGinn. Sophie takes Con to see Alex's exasperated ex-wife, who says she doesn't know where Alex is, and that she hated Layla. On the drive back they pass The Bluebell and Con tells Sophie how he believes Layla was killed. Sophie takes him back to her house, where Layla had lodged. Sophie tells him that Layla was in the IRA and that Sophie's husband was killed because he was with her at the wrong time. After he and Sophie embrace, Con runs off. Sophie catches up with him as he is about to enter The Bluebell. Entering the pub, they are quickly threatened by a loyalist gang. Geordie rescues them and makes them meet some Protestant victims of the Troubles before telling Con that Republicans killed Layla, and that Sean knows the truth. Rushing to McFadden's Bar, Con finds Sean and threatens him. Sean tells him that Layla was part of a violent and extreme IRA faction. The note Sean had found was a list of initials. At that moment the bar TV announces that Con's friend Artie Flynn has been shot on his 24-hour leave. 'AF' is on the list, as are 'TM' and 'CE'.

Con and Sophie go to Armagh, where another meeting is taking place, which Alex may be attending. They go to Alex's brother-in-law's house and see him leave. Con breaks in and threatens the brother-in-law in front of his child. Sophie disturbs him and is upset. They drive to the farm for the meeting and are immediately dragged out of the car. They are held while Thomas and his henchman wipe out Rory McGinn's hardline faction, including Alex. It becomes clear that Thomas had hired Sophie to watch Con; Thomas now returns Con's 24-hour pass. On the drive back, a shaken Sophie asks Con why he is a prison 'lifer'. He tells her he killed two elderly sisters in a case of mistaken identity.

Back at the prison, an IRA ceasefire is announced and Thomas is mobbed by the inmates. He goes to Con's cell, where he praises Rory as a good republican but justifies the massacre as politically necessary to safeguard the future. Con asks him why he killed Layla. Thomas tells him that it broke his heart and Con replies that he understands too well.