In 1909 Arizona, convicted killer Zach Provo works on a chain gang laying railroad track. Provo kills one guard with an iron spike and shoots the other with the dead man’s rifle. After the prisoners break their chains with sledgehammers, most escape into the desert, but six stay with Provo: Cesar Menendez, George Weed, Will Gant, Portugee Shiraz, Mike Shelby, and Lee Roy Tucker. All are seasoned criminals except for Shelby, who is nineteen years old. Menendez, a Mexican, objects to working with the bigoted Lee Roy, but Provo, who is half Navajo, believes Lee Roy to be a useful ally. The gang takes a freight train to Gila Bend to get horses and supplies, and Provo informs the others of his plan to get revenge on former territorial captain Sam Burgade. The next day, in Tucson, Sam enters the office of his successor, Noel Nye, offering to come out of retirement to assist with Provo’s capture. Noel does not require Sam’s help, believing that modern technology will provide all the assistance needed. Sam proves his worth by finding evidence of the gang on the train when it arrives in Tucson. He then notifies the press that a shipment from the U.S. Mint is due in town, hoping to attract Provo’s attention. Impressed by Sam’s understanding of Provo, Noel puts him on the case. That night, Sam advises his daughter, Susan, to marry Hal Brickman, a soft-spoken agricultural engineer from Massachusetts. Susan dismisses the idea, certain that Hal has none of the heroic characteristics of her father. However, when Susan learns that Sam is returning to work, she fears for his safety and begs him to reconsider. He tells her of the time Provo killed four men while robbing a train, leading to a shootout with Sam and his posse that left the outlaw’s young Navajo wife dead. Knowing that Provo is intent on revenge, Sam believes he has no choice but to accept the assignment. Hal arrives moments later, and Sam, hoping to secure his daughter’s future, encourages the young man to visit as often as he likes. Meanwhile, as the gang robs a general store, Lee Roy refers to the storekeeper’s pregnant wife as “a Mexican pig.” With Provo’s approval, Menendez plunges a knife into Lee Roy’s back. Shelby, the literate member of the gang, reads Provo a newspaper article announcing the shipment of new money headed for Tucson, to be guarded by Sam upon its arrival. Aware that he is walking into a trap, Provo leads the gang to Tucson under the pretext of not disappointing Sam. After the shipment is safely in the bank, Sam puzzles over Provo’s absence, but when he returns home, he discovers that Provo has kidnapped Susan. Sam brings his plight to Noel, who maintains his faith in modern technology, until it becomes apparent that Provo has cut the telephone lines between Tucson and Phoenix. Positive that Provo is headed north to retrieve a cache of buried gold on the Navajo reservation, Sam and Nye organize a posse. Hal insists on joining, undeterred by Sam’s refusal to allow a “greenhorn” to come along. As the posse closes in on Provo, he offers his henchmen $4,000 in gold if they help him to defeat Sam. He then assigns Shelby to guard Susan as a deterrent to Gant and Shiraz, who are unable to control their sexual urges. Upon reaching Navajo country, Provo bribes the tribal police to allow the gang onto the reservation, and to bar the posse from entering. Fearing a reprisal from the Navajo, the posse turns back, leaving only Sam and Hal to face the kidnappers. The two men camp at the bottom of a hill, and set a trap in case one of Provo’s men is sent to spy on them. Before long, Weed is caught in the trap and, under threat of death, reveals Provo’s position to Sam. After tying Weed to a tree, Sam and Hal move their camp further up the hillside. The next morning, when Provo discovers his nemesis hiding nearby, he tries to draw Sam into the open by allowing Gant and Shiraz to have their way with Susan. Realizing that Provo is laying a trap, Hal knocks Sam unconscious before he can rescue his daughter. That night, Sam and Hal use gunpowder to start a brush fire that consumes the hillside. Provo, Menendez, Shelby and Susan take refuge on the other side of the hill, while Shiraz is burned alive. Abandoned by the gang, Gant hides among the rocks until morning, when he attempts to steal Sam’s horse. Sam, enraged over the rape of his daughter, bludgeons Gant to death with a rifle stock. As Sam makes his way up the hill, Provo and Menendez try to ambush him, but Sam foils the plot and kills Menendez. While attempting to avoid Sam, Shelby runs directly into Hal. Both men draw their weapons and Shelby is killed. Susan goes to her father, unaware that Provo is hiding nearby. The outlaw surprises Sam and inflicts several nonfatal gunshot wounds, but when he is about to cut the lawman’s heart out with a knife, Sam produces a pistol and kills Provo with a single shot. As Sam lays on the ground bleeding, Susan and Hal run to his aid.