A convict uses a fake gun to start a full-scale prison escape.

At the Colorado State Penitentiary near Canon City, inmate Carl Schwartzmiller and others are secretly making crude weapons to use in a prison break. Jimmy Sherbondy, an inmate who is opposed to the breakout, unwittingly becomes involved in the scheme when one of the convicts hides a gun in the projection room where he works. Jimmy later embraces the plan, though, when he discovers that he faces another ten years in prison. On 30 Dec 1947, Sherbondy initiates the prison break by sawing through his cell bars. While some of the twelve escapees from the solitary confinement cell mix with inmates returning from the mess hall, they are spotted by Officer Gray. Gray is nearly beaten to death by the escapees, and is then taken as a hostage. Once outside the prison walls, the escapees enter the small town of Canon City, where a siren alerting the town of the prison break has sent the population scrambling to their homes. While some of the escapees scatter throughout the town, six of them take refuge in the home of Mr. and Mrs. Oliver and their daughter. Inside the Oliver home, the escapees use threats to demand new clothes and weapons. When Mrs. Oliver attacks Schwartzmiller with a hammer, the escapees overpower her and then raid the Smiths' home. There one of the inmates tries to rape the Mr. Smith's seventeen-year-old niece, but Sherbondy intervenes and stops him. When the police arrive, the escapees use Mrs. Smith as a human shield and engage the police in a shootout. All but Sherbondy are either killed or captured by the police in the ensuing gun battle. Sherbondy escapes to the home of Mr. and Mrs. George Bauer, whose young son Jerry is suffering from appendicitis and is in need of medical help. Though planning to flee with the Bauers' car, Sherbondy has a change of heart and allows the boy to be taken to a hospital instead. En route to the hospital, Sherbondy approaches a police roadblock and willingly surrenders himself. Sixty-one hours after the prison break, Sherbondy, the last of the fugitives, is arrested and sent back to prison to rejoin the other escapees in solitary confinement.