El Boy (Juan Manuel Bernal) lives in poverty with his alcoholic aunt, Chenta (Dolores Beristáin), in Mexico City. When his friend Mauricio (Demián Bichir) comes to visit, El Boy introduces him to the local underworld of small-time criminals. After killing a guard during a botched kidnapping, El Boy escapes to avoid the police. Mauricio betrays him, taking advantage of his absence to sell his aunt's mortgage, then courting a woman while pretending to be El Boy.