Once upon a time, Billy (Jake Gyllenhaal) was famous in the boxing world for his fierce and cold left fist. For a time, no one could beat him and he was a well-deserved boxing champion. However, an accident caused Billy to lose his beloved wife Maureen (Rachel McAdams). This tragedy completely broke Billy. He began to give up on himself. Not only did he give up his career, he even began to drink and take drugs. As a result, he was deprived of the custody of his daughter Leila (Oona Laurence), and Leila was sent to a welfare institution. The departure of his daughter made Billy gradually sober up. He was extremely disappointed with his poor current situation and decided to change his ways. Billy hopes to be able to stand on the boxing ring again. He found coach Wells (Forest Whitaker), hoping that he could help him and regain everything he lost.