Sentenced to five years in prison for a robbery, Rudy Hernandez is walking the straight and narrow. He studies, works in the prison garage and steers clear of trouble, hoping he'll gain parole in three years. Meanwhile, imprisoned mob boss Lou Gannon has other plans for Rudy. He makes him the fall guy for an inmate's stabbing, ruining Rudy's parole chances and recruiting him to be a point person in a massive breakout. On the day of the jailbreak, prisoners wield machine guns built from smuggled-in parts. Take guards hostage and dynamite the main gate. As the violence surges, Rudy discovers what he isn't supposed to know: The part of the breakout scheme Gannon didn't reveal to him. Robert Blake (In Cold Blood) plays Rudy, ensnared in the Big House tumult. Gene Evans (The Steel Helmet) plays domineering Gannon. Timothy Carey (Paths of Glory) and John Qualen (The Grapes of Wrath) are among the costars.