Román Zegarra, amateur boxer, is rejected by a gym when it is discovered that he has never fought in La Mugre, the underground fighting event where all the men in the city compete. Pressured by his friends and by his family’s financial needs, Román agrees to fight in this brutal event. To do so, he recruits El Puma, a former wrestler who takes him to the tournament. In his first fight, Román ends up beating his opponent to death, becoming trapped between the horror of what he has done and the roar of the crowd chanting his name.