Marshal "Sundown" Jim Majors arrives in the town of Reservation to help settle a fiery range war, and on the evening of his arrival, small rancher Clem Black is gunned down by sharpshooter Dale, who is a member of Ben Moffitt's gang. Clem's daughter Tony then bitterly castigates Catherine, daughter of rancher Andrew Barr, for her father's part in the murderous occurance. Jim learns from Tony that Barr obtained Clem's land through legal but unethical means, and when the other small ranchers tried to stand up to Barr, he brought in Moffitt and his hired guns for protection. The next day, determined to clean up the town, Jim decides to face the challenge sent by the gang when they rob the mail coach of its contents and state that they will be at their hideout. Jim travels alone to the hideout, where he succeeds in outwitting the gang and retrieving the mail sacks. Infuriated, Moffitt tells Barr that he is going to get rid of Jim, despite Barr's reluctance to be involved in the murder of a U.S. marshal. Catherine rides ahead to town to warn Jim of the upcoming showdown, and when Moffitt and his men arrive, Jim shoots Dale. A gunfight ensues, involving the gang, Barr's men and the small ranchers, led by Dobe Hyde and Nat Oldroyd. With Tony's help, Jim gets the factions to stop shooting, and makes a speech in which he insinuates that the sneaky Dobe and Moffitt are in league and are double-crossing Barr and Oldroyd. The next morning, Hyde goes to Moffitt's hideout, and there suggests that they team up. Moffitt is reluctant, so Hyde tells him that he will organize the ranchers to attack Barr, and during the fight make sure that Oldroyd and Barr kill each other. The way will then be clear for Dobe and Moffitt to run the town. As Moffitt is agreeing to the plan, they discover that Barr has heard their conversation. Moffitt shoots Barr, then sends Dobe to instigate the raid. Jim, who had followed Dobe, rushes to the Barr ranch to warn Catherine and her brothers, Ring and Dan. After another fight, Jim is able to convince Oldroyd and the Barrs that they have been double-crossed, after which they all ride to town to confront Moffitt, Dobe and their men. Tony and Dobe kill each other during the shootout, and Jim shoots Moffitt as he tries to escape. The townspeople then prevail upon Jim to stay, and hotel clerk Broderick sends for a preacher so that Jim and Catherine can be married.
