 When young Danny Lambert (Peter Votrain) runs away from camp in south-central Colorado, he becomes the object of a park-wide-search by his wealthy father Robertson Lambert (Willis Bouchey). He is found by Jerry Barker (Ralph Meeker) and told to wait at an abandoned look-out tower while he goes for help. Instead, Barker calls the father and demands $200,000 ransom. The money is delivered and Barker buries most of it. Meanwhile, the panicky boy has fallen from the tower to his death, and Barker drops the body off a cliff. The FBI, led by James Madden (Reed Hadley), capture Barker but can t convict him of kidnapping and he is given only five years for extortion and sent to Casabel Island Prison. There he is assigned a cell with Rollo Lambar (Broderick Crawford), Alamo Smith (Lon Chaney, Jr.), Benny Kelly (Charles Bronson) and Machine Gun Mason (William Talman.) The FBI have now traced an affiliation between Barker and Emily Evans (Felicia Farr as Randy Farr), a nurse at Danny s camp. The five cell-mates, led by Rollo, who plans to kill Benny and dress him in Barker s clothes to throw off the police, execute an underwater prison escape, and head north for the ransom money.