U.S. Marshal Dana Andrews as Johnny Reno is on his way to the town of Stone Junction on personal business. As he rides through the desert, the fugitive Conners brothers—Tom Drake as Joe Conners and John Agar as Ed Tomkins—spot him and open fire from an ambush. Reno defeats them, wounding Joe and killing Ed. He takes Joe into custody, retrieves Ed's body, and rides with them toward Stone Junction. On the way, Joe explains that a posse from the town has been after them, along with the local Native American tribe led by Paul Daniel as Chief Little Bear.
Arriving in Stone Junction, Reno is immediately accosted by the mayor Lyle Bettger as Jess Yates and the town sheriff Lon Chaney Jr. as Hodges. Hodges tells Reno he won't put Conners in his jail, and Yates demands that Conners be turned over. Reno refuses and browbeats Hodges into allowing him to put Conners in his jail, infuriating Yates. A number of the townspeople openly show hostility to Reno, even attempting to shoot Conners in the street, including Yates's daughter. Reno asks after Nona Williams, Jane Russell as Nona Williams, a girl he once loved, and learns she now runs the local saloon.
At the saloon, Yates threatens Reno and orders him to leave town without his prisoner. When Reno refuses, Yates attacks him and the two men fight. Reno defeats Yates and goes back to the jail, where he finds out that Sheriff Hodges has handed out rifles to some of the townsfolk on Yates's orders. Reno asks where Nona would be if not in the saloon, and Hodges sends him to Nona's ranch outside of town. Reno rides off to see her. Meanwhile, Yates gathers his men armed with the rifles, ready to act. Reno arrives at the ranch and starts to talk to Nona about their past, but they are interrupted by two of Yates's henchmen and held at gunpoint. Reno grows suspicious and voices a theory—that maybe Conners is in fact innocent and the townsfolk want him silenced. The two henchmen inform him that it doesn't matter, and that they'll just hold him at the ranch until Conners is dead. Reno manages to throw a piece of furniture at the guards, distracting them long enough for him to draw and shoot them both dead. He reconciles with Nona and sets off for the town, where he arrives just in time to prevent Hodges from turning Conners over to the armed mob outside. Reno holds the crowd at gunpoint and has Hodges disarm them. The sheriff, his backbone strengthened by reinforcements, seizes the rifles back. Reno and Hodges hole up in the jail where Reno questions Conners and learns that he and his brothers were strangers in town who were plied with drink by the "friendly" townsfolk.
After this, Hodges notices a disturbance in the street and they emerge to find the mayor and his men organizing an evacuation of the town under the guise of fear of an Indian attack. All the women but Nona leave the town along with the children and most of the men. Only about a dozen of Yates's confederates stay behind to "defend" the town. Hodges is now convinced of the guilt of the mayor and agrees to follow Reno's lead, but they are barricaded in the jail with no one left in town but the hostile men. Night falls, and Yates takes Nona prisoner and sets up an ambush in the street. He baits Reno by loudly playing a song memorable to Reno and Nona on the player piano. Reno leaves the jail, telling Hodges to cover him. When the men notice Reno is in the street, they leave the saloon and Nona is able to escape. Reno and the rogue townsfolk start shooting at each other in the street. When one man almost shoots Reno in the back, he is killed by Sheriff Hodges, but Hodges is killed in the ensuing shootout.
Reno makes it back into the jail, frees and arms Conners, and tells him to watch the back door. Yates and his men approach with a wagon and torches, intending to burn them out of the jail. Reno sends Nona to get help and sets up on the jail roof with some dynamite. He succeeds in killing several of the attackers and scattering the others and sneaks back inside. Conners kills one man who tried to kill Reno as he returns to the back door of the jail. The situation continues until sunup when one man loses his nerve and deserts Yates, riding into the desert where he is captured and tortured for the truth by Chief Little Bear's tribe: Yates and his friends killed the chief's son because he fell in love with the mayor's daughter, who is half Native American. Yates does not want anyone to know that he was once married to a Native American woman.
At the town, Conners, having had enough, manages to surprise Reno and knock him unconscious. He is unwilling to let Reno die for him and attempts to surrender in exchange for Reno's safety. Instead, Yates takes them both into the street where they are told what really happened and that the story will be that Conners killed Reno trying to escape. Chief Little Bear and his tribe arrive with their prisoner just in time. The prisoner tells Yates he confessed, only to immediately be shot dead by the mayor. The tribe's warriors and the renegades begin exchanging bullets. In the confusion, Reno is able to break free. He and Conners fight along with the tribe, and kill Yates and all his men. Yates is strangled when his foot gets caught in a rope lying on the ground, which turns out to be the noose he had planned for the Conners brothers. Afterwards, Reno rides to the fort and tells the townsfolk and Yates's daughter what really happened. He encourages the people to go back to the town and rebuild. He and Nona then depart to start their lives together.
