In 1975, Irish-Protestant Allistar Little, a 17 year old youth murdered 19 year old Catholic Jim Griffin. The murder was witnessed by Jim's brother, 11 year old Joe. Little was eventually arrested and served 12 years, while Joe, whose own mother blamed him all his life for not stopping Little from shooting Jim, has let his anger consume him.
30 years later, Little (Liam Neeson) and Joe (James Nesbitt) are brought together for a television special to broached the topic of what has occurred. Little, who has become remorseful for what he did, has taken to public speaking in order to prevent similar things from occurring to others. Little knows that Joe doesn't want an empty apology from him, but the stark truth about what happened that night. However, Joe, who had planned to kill Little at the interview, freaks out and leaves before anything can take place.
Little eventually tracks down Joe and asks to meet. They wind up at Joe's old house where he tries to stab Little. They engage in a fight with Little just trying to defend himself, and ends with them falling through the second floor window. They survive, and Little finally tells Joe the truth; he targeted his brother because he wanted the glory that fighting for his side would bring. He tells Joe to forget about him, and live for his family, and not for the rage that will continue to consume him. Little limps away, vowing never to come back.
Joe, able to let go, begins to attend therapy and work out his feelings. He calls Little one last time, to tell him they are done. Little needs a moment to compose himself in the crosswalk of the street, overcome with the knowledge that they can both move on. He then continues on with his day, both men finding the strength to live their lives once more.