A warden and his assistant clash over prison reform, triggering a violent riot.

In the first half of the twentieth century, at California's maximum security Folsom Prison, unhealthy conditions and brutal treatment are considered by the cruel, old-school prison warden, Rickey, to be the only way to handle the three-time convicted felons. One Sunday, against the advice of ringleader Chuck Daniels, several prisoners attempt a breakout. Although the riot is quickly suppressed by Rickey, two guards are killed along with several prisoners. Harsh punishments are meted out to those involved, and a Sacramento Press reporter, Jim Frazier, investigates a rumor that one of the instigators of the rebellion was beaten until paralyzed. Because of the prison's recent problems and changing societal views regarding the treatment of inmates, the prison's board of directors orders that new blood be infused in the system and sends penologist Mark Benson to serve as captain of the guards. On his way to the prison, Benson meets Jane Pardue, whose good-natured, young, inmate husband Red has truly reformed and anticipates a parole. Rickey and his right-hand man, Sgt. Hart, show Benson around, and although Benson acknowledges that the hardened men have committed the most heinous of crimes, he also notes that they suffer from inhumane conditions, spoiled food and senseless, morale-shattering regulations. When Benson expresses his desire to make changes, Rickey condescendingly allows him free reign, expecting that he will soon discredit himself with his weak, psychological approach. Benson orders the cleaning of the living and work areas, arranges for better food, including meat, to be supplied by the prison ranch, and allows the prisoners to converse during meals. He puts an end to impulsive beatings and insists that the uneducated, trigger-happy guards come to work clean and behave professionally. Believing that parolees, such as Red, need help in adapting to life "outside," he offers them job-hunting assistance. Later, Red, a demolition expert working in the prison quarry, is sent to town with a guard to pick up supplies. As the guard checks them out of the gate, Red realizes that a fellow prisoner, Nick Ferretti, is hiding under the car seat. Knowing that he will be blamed for Ferretti's escape, Red silently alerts the guards and Ferretti is captured and placed in solitary confinement. Fearing the prisoners' retribution, Benson urges Rickey to move Red to a different cellblock for his safety, but Rickey makes little distinction between the inmates who make trouble and those who cooperate, and refuses. Troubled by his act of betrayal, Red tells his cellmate Daniels, but the hardened criminal says that Red had no choice, as he would have taken the rap for assisting in Ferretti's escape and had his parole unfairly cancelled. Daniels, who fully trusts Red with his own carefully laid escape plans, worries that the prisoners will learn about Red's tip-off. Meanwhile, from inside his "solitary" cell, Ferretti has learned from an eavesdropping prisoner that Red turned him in and bribes another prisoner, Tinker, to avenge him. Because Red has a good reputation among the prisoners, Tinker at first cannot believe the accusation, but his greed decides his actions. Red is killed in an explosion in the quarry on the day before he is to be paroled, and Daniels, guessing who is behind the accident, secretly plans revenge. After telling Jane the whole truth about Red's death, Benson accuses Rickey of murder, as he did not try to protect Red, and in retaliation, Rickey revokes all of the reforms. Life again becomes unbearable for the prisoners and Daniels, who has been secretly stockpiling explosives for an escape, prepares his followers for a breakout. He manages to take a cell guard, then Hart, as hostages, and orders Rickey to release them. Disguising himself as a prisoner, Rickey gains entrance into the cellblock and begins shooting, but when he is killed, a shoot-out commences between guards and prisoners. After taking over, Benson calls in the state militia, cuts the electricity in the cellblock and gives Daniels five minutes to surrender. Knowing he is defeated, Daniels releases the prison guards and the uninvolved prisoners, except Ferretti and Tinker. Tinker, who knows Daniels plans to avenge Red's death, grabs a gun from one of Daniels' cohorts and shoots, setting off the explosives, and all in the cellblock are killed. In the following years, with men like Benson in charge, the prison board modernizes the facility and its programs, so that the prisoners have a better chance of being reclaimed for society.