Belfast, the mid-1990s. Catholic Roisin 'Rosie' Willis lays a bouquet outside the house where her Protestant husband Paul was shot in bed beside her 12 years earlier. Meanwhile, her 16 year-old son, John, is out with his friends, robbing a shop. Billy McVea, a former UVF gunman, is a 'born again' preacher, telling his congregation that he thought he was beyond redemption until his wife helped him to convert.

A TV news bulletin shows Sinn Fein spokesmen calling for reconciliation. Rosie angrily denounces them to John and again reports Paul's unsolved murder to the RUC, who see the case as politically embarrassing in the new ceasefire era.

Billy runs a gym, teaching youths boxing. Outside he sees a tramp, who he recognises as Davy, a member of his old UVF squad. Davy was banished but told the UVF that his mother recently died. Panicked by the encounter, Billy informs the UVF that Davy's mother died years ago, knowing that Davy will be killed for this deception.

After Rosie burns John's contraband, he rows with her and her sister Jean, denouncing them as Fenians. John joins a sectarian riot but is injured and seeks shelter in Billy's church. Billy encourages him to box at the gym. Billy is increasingly troubled by memories of his paramilitary past. He dislikes his own son, the sullen Harold, but is himself disliked by his own father. Rosie visits the gym and a mutual attraction develops between her and Billy.

Rosie is called into the police station. The detectives tell her that Paul was a UVF man probably killed by his own side - not telling her this was because he was a RUC informant. Devastated, she revisits Republican West Belfast for the first time in years to find Jean. Meanwhile John takes Billy, who he now hero-worships, back to his house. He shows him a picture of his father and Billy is horrified to recognise him as a man that he killed.

Rosie tells John that the UVF killed Paul. John claims that it was because Rosie is a Catholic and runs away, throwing bricks at the paramilitary pub and local people before being cornered and attacked. Billy gives a sermon saying that he would like to move from the dark to the light. Rosie hears of John's injuries and goes to his bedside at the hospital, where Billy joins her. He confesses his crime to her and then walks into the RUC station to give himself up.