The story takes place in Northern Ireland in 1971. The conflict between Protestants and Catholics continues to intensify, and the war is imminent. The situation is very critical. Gary (Jack O'Connell) is a young British soldier. His superiors send him to Belfast, which is the main battlefield of the civil war, full of stray bullets, angry crowds and speculators with ulterior motives. In a conflict, Gary and his companions fly to chase the thief. However, when Gary came back to his senses, he found that he was alone in the chaotic streets. What's worse, he was in the enemy camp, which means that everyone around him may want to take his life. In order to return to the station, Gary began a long trek. What awaited him along the way was a strange and complex environment and vicious desperadoes.