Family man Wade Porter (Stephen Dorff) is living the American Dream with his girlfriend Laura (Marisol Nichols) and their son Michael. However, their dream becomes a nightmare when Wade unintentionally kills a burglar on his lawn. By attacking an unarmed intruder after he exited the house, he is arrested and charged with murder.

During the bus ride to prison Danny Sampson (Chris Browning), leader of the local Aryan Brotherhood, stabs a man and hides the knife with a young Aryan member named Snowman (Johnny Lewis) who is sitting behind Wade. In a moment’s panic, Snowman hides the knife under Wade’s seat and forces him to deny knowledge of it. As a result, Wade is sent to solitary confinement until the stabbing can be investigated. Lieutenant Jackson, (Harold Perrineau), interrogates Wade about the stabbing but he doesn’t cooperate with the investigation. Jackson decides to send Wade to the Security Housing Unit (SHU) where he is the commanding officer.

John Smith (Val Kilmer), an inmate who is serving a life sentence becomes Wade’s cellmate in “the SHU”.

Life is tough in the SHU for Wade. Inmates are under 23-hour lock-down, and he can’t have visitors for the first three months. Wade immediately realizes that the daily hour of yard time consists of inmate fights, on which the guards bet. At different points throughout the film, it’s shown that not all of the guards are in favor of Jackson’s methods.

In addition to the prison violence, Wade’s regular visits with Laura start to take their toll on their relationship. Michael has nightmares after one of his visits, and the family’s finances are running low. Laura, at the encouragement of her mother, breaks up with Wade through a letter. Enraged, and seemingly having nothing to live for, Wade breaks down and resorts to fighting the prisoners.

After talking to John, Wade devises a plan that can reveal the truth about the violence in the prison, and possibly get him released.