In the town of Red Rock, Steve Farrell, Randolph Scott is a gun salesman who demonstrates the new Colt .45 repeating pistols to the sheriff. The moment is cut short when men arrive to transfer a prisoner, Jason Brett, to another jail. As Brett is being led away, he overpowers the guards, grabs Farrell’s pistols, shoots the sheriff, and makes a daring escape. Convinced Farrell helped facilitate the breakout, the townspeople arrest the gun dealer. Brett then launches a brutal spree of robberies and cold-blooded murder, proving that regular guns can’t rival his Colt .45s.
Farrell is released from jail and pursues Brett into Texas, where he encounters a band of Indians led by Walking Bear—the lone survivor of Brett’s latest attack on a stagecoach. Chief Walking Bear, Chief Thundercloud, provides Farrell with crucial knowledge about Brett’s plan. Determined to stop the gang, Farrell boards the stage in a bid to confront them, wielding his own Colt .45s. Among the passengers is Beth Donovan, Ruth Roman, who tries to avert a violent showdown. Yet Farrell’s instincts tell him something deeper is at play, especially when he spots a white scarf at the window—a signal he fears marks Beth as a conspirator.
Beth escapes on horseback while Farrell honors his duty to aid the wounded stagecoach driver. Unbeknownst to him, Beth is married to Paul Donovan, one of Brett’s henchmen, who is secretly aligned with the Colt .45 Gang. Beth returns to her cabin home, used by Brett and his crew as a hideout, and she soon learns that her husband is fully involved in the criminal scheme. When she confronts him, Paul locks her away in a shed, and she manages to escape, racing to town to reveal what she knows. Paul wounds her before Farrell can intervene, prompting Farrell to haul Beth onto his horse and ride to Walking Bear’s camp for safety.
Beth regains consciousness and warns Farrell about Brett’s plan to seize control of Bonanza Creek. Meanwhile, the Indians discover Paul dead, his body left across a horse and saddle—executed with multiple gunshots. Back in town, Sheriff Harris—Alan Hale—and Brett’s gang lay a trap for Farrell. The Indians spring to Farrell’s rescue, killing one of his captors, but Harris still manages to mount a horse and press on toward the showdown. Farrell and the tribesmen ride into Bonanza Creek, where Brett’s men are scattered, and the Indians rout the gang.
Brett, who has Beth as a hostage, camps out in the sheriff’s office. Harris arrives to warn Brett, but he dies just inside the door. Beth manages to slip free during the tense standoff, and Farrell bursts into the jail to face Brett. With Brett low on ammunition, a fierce struggle ensues, guns are drawn, and a final shot rings out. Brett steps into the street, takes a few faltering steps, and collapses dead. In the aftermath, Farrell emerges from the jail and is welcomed by Beth, signaling a hard-won, uneasy victory over the violence that plagued Red Rock and Bonanza Creek.
