Mick O'Brien (Sean Penn) is a 16-year-old Irish hood from Chicago. While most of Mick's crimes involve snatching purses, vandalism, and getting into brawls, he aspires to bigger and better things, which leads him to attempt ripping off a rival hood, Paco Moreno (Esai Morales). Everything goes wrong: Mick's partner and best friend (Alan Ruck) is killed, and Mick, while trying to escape the police, accidentally runs over and kills an eight-year-old boy who happens to be Paco's kid brother.

Because he's under 18, Mick is sent to the Rainford Juvenile Correctional Facility rather than a state prison for adults. However, as the film makes clear, this "juvenile correction facility" is not a place where troubled kids are reformed, but rather a place where they grow tougher, angrier, and more prepared for a life of adult crime. Most of the wardens and counselors seem to have resigned themselves to the role of zoo keepers, with the exception of Ramon Herrera (Reni Santoni), a former gang member who talks tough to the inmates, but holds out hope for some of them, especially Mick.