After outlaws ambush and kill a young federal marshal, who was part of a posse chasing them, one of the outlaws, Cherokee Kid, who is suffering from a toothache, convinces his cohorts that it is safe to go to the town of Bitter Spring to see a dentist. Allan "Rocky" Lane, a federal marshal and colleague of the murdered man, follows them there, but is recognized by Cherokee's waiting cohorts, Buck Madsen and Tulsa Tom. A gunfight ensues, but the two outlaws get away, leaving behind Cherokee, who has been gassed unconscious by the town's barber-dentist, Nugget Clark, with his modern gas mask. Nugget, who is also the city marshal, locks Cherokee in the jail, but the outlaw soon shoots his way out, killing the deputy, Dan Longley, after a gun is secretly smuggled into his cell by William Oakes, the town's cafe owner and community leader. In town, Oakes, who is secretly working with the gang, then gets Nugget fired for incompetence and directs suspicion toward Oakes's former secret partner, Sam Webb, a reformed parolee who now runs a farm with his sister Elizabeth and younger brother Johnny. Although Sam would like to turn Oakes in, Oakes threatens to tell the law that Johnny once assisted with a bank holdup when Sam was away. However, Oakes's hastiness in removing Nugget from the marshal's office makes Rocky suspicious of him. After noticing that Cherokee's food tray, which is delivered from Oakes's cafe to the jail, is sticky underneath, Rocky guesses that a gun was taped to the bottom with a new kind of mending tape and asks for Nugget's unofficial help in solving the case. Meanwhile, Sam decides that Cherokee has to be stopped from murdering innocent people, even at the risk of Johnny spending a few years in jail for his one crime. Breaking the rules of his parole, Sam puts on a gun and confronts Oakes, but Rocky sees him armed and takes him to the jail for questioning. Sam hesitates to reveal Oakes's criminal activities and Cherokee is able to shoot him through the window before he gives Rocky any useful information. Rocky shoots back, but Cherokee rides away. However, Johnny shows up and assumes that Rocky shot Sam. Because Johnny's hotheadedness is dangerous for everyone, Rocky and Nugget lock him up to cool off. Meanwhile, the doctor decides to keep Sam at the jailhouse under Elizabeth's care, as the bullet is lodged dangerously close to his heart. Having seen Oakes watching idly from across the street when Cherokee shot Sam, Rocky becomes even more suspicious of the businessman, and when he rides out of town, Rocky follows, unaware that Oakes is setting a trap for him. However, Nugget notices Buck Madsen following Rocky and rides out to warn him, leaving Elizabeth with her brothers at the jailhouse. After Nugget leaves, Johnny convinces Elizabeth to free him, but then grabs a gun and goes after Rocky for supposedly shooting Sam. Outside of town, Rocky rides into the ambush near the outlaws' hideout cave, but with Nugget's help, apprehends Cherokee, Tulsa and other members of the gang, except for Oakes, who has returned to town during the skirmish to finish off Sam. At the cave, Johnny slips up from behind and is about to shoot Rocky, when he realizes that Cherokee was the man who wounded Sam. When Cherokee tries to draw a hidden gun, Johnny fires at him first. Aware that Oakes is missing from the group, Rocky rides swiftly back to town. He gets to the jailhouse in time to save Sam, but then must fight Oakes. After a struggle, Rocky knocks him out, and Johnny and Elizabeth apologize for distrusting him. Later, after the remaining outlaws are locked up, Rocky tells Nugget that he will not pursue Johnny for his part in the bank holdup, as Johnny was young at the time and did help to stop Cherokee. After leaving Nugget to tell a young admirer exaggerated stories of his previous triumphs, Rocky rides off to his next assignment.