While the Prison warden (real-life warden Frank Eyman) of a state prison is away, the isolation block erupts and 35 of the most violent criminals (led by Gene Hackman) stage a riot and take over their portion of the prison. Cully Briston (Jim Brown), in for five years and awaiting his eventual parole, wants no part of the riot. He impulsively gets involved, defending a prison guard and protecting him from the maniacs in the block.