In Hays City, Kansas, buffalo hunter and gambler Bat Masterson kills cavalry sergeant Ernie King in self-defense. Although wounded, Bat takes his best friend Ben’s advice and flees to Dodge City to stay with his brother, state marshal Ed Masterson. Bat arrives in town at the height of the election campaign for town sheriff and is befriended and tended to by the town doctor, Sam Tremain. After introducing Bat to his fiancée Pauline and her father, Rev. Howard, Ed explains that the current sheriff, Jim Regan, is a former gunman, as are his cronies. Constricted by the legal boundaries of marshaling, Ed reveals his determination to run against Regan in order to clean up the lawlessness that has taken over the town. Bat remains indifferent to Ed’s ambitions, but startles his brother and the Howards with his announcement that he will remain in Dodge City and purchase a saloon. Soon after, Bat visits the Lady Gay saloon, where Sam presents him to the proprietor, Lily, a widow whose husband was murdered for refusing to pay Regan protection money. Lily admits that she is near bankruptcy since Regan forced the departure of her dealers, but she stubbornly refuses to close. Bat offers to invest six thousand dollars in the Lady Gay for a half interest and, although stunned, Lily quickly agrees. Upon seeing the renovations being made to the Lady Gay, Regan approaches Bat to make an offer for the saloon, then threatens the gambler when he refuses. Unknown to Bat, acquaintance and fellow gambler Dave Rudabaugh has followed him to Dodge City, bitter over the death of King, his cousin. After the successful opening night of the reinvigorated Lady Gay, Bat, Lily, Sam and Ed close up, unaware that Dave and, separately, two of Regan’s henchmen, are stalking Bat. As Dodge City erupts into the usual Saturday night drunken rowdiness, Dave shoots Ed in the back under the cover of the revelry. Regan’s henchmen then burst in and are killed by Bat, who believes they shot Ed. After Ed’s funeral the next day, Dave pretends to have just arrived and accepts Bat’s offer to work as a dealer at the Lady Gay. Pauline visits Bat to recover some of Ed’s personal effects and accuses him of bringing about Ed’s murder. Bat admits his brother was an exceptional man, but challenges Pauline over the depth of her feelings for him. Upon discovering that Regan has left town, Bat searches the Kansas countryside for him in vain, then, knowing Regan must return to Dodge City for election day, goes back to Dodge after visiting Ben in Hays City. Lily tells Bat that Regan has indeed come back to town, but warns him not to kill him as he is still the sheriff. Howard then calls on Bat to tell him that the town committee wants him to take Ed’s place as their candidate for sheriff. Bat scoffs at the notion, but Howard insists that Bat stood up to Regan’s initial challenge over the saloon and, despite being a known gambler and gunslinger, is preferred over Regan. Bat restates his determination to avenge Ed’s death, but when Regan arrives unannounced, Bat begins a fistfight with him and afterward abruptly agrees to run for sheriff. With the support of the committee and law-abiding citizens, Bat is elected sheriff and declares that although he will allow gambling and saloons to remain in business, they will be restricted to set hours. When Pauline expresses skepticism over Bat’s abrupt embrace of the law, Bat reminds her that he is Ed’s brother. Regan and his men attempt to stir the town up for its usual Saturday night revelry, but Bat quells their antics. Bat then begins spending time with Pauline, but when he suggests they date, she demurs, admitting she could never be involved with a saloon owner. Bat promptly goes to Lily to give up his half interest in the Lady Gay and Lily sadly realizes Bat’s involvement with Pauline. Back in his rooms, Bat receives a visit from Ben who is alarmed because his younger, simple-minded brother Billy has inadvertently shot and killed a Hays City deputy. Although Bat agrees that Billy ought to have been institutionalized long ago, he refuses Ben’s plea to help him break his brother out. Meanwhile, Dave sneaks into Lily’s room and declares his attraction to her. When she threatens to cry out, Dave goads her into calling for Bat, revealing he murdered Ed and intends to kill Bat for the death of his cousin. Drawn by Lily’s screams, Ben and Bat rush to her room, and after Dave wounds Ben, Bat kills the gunman. With Ben unable to help Billy, Bat reluctantly agrees to intercept the stagecoach transferring the boy to the prison where he is to be executed. Sam joins Bat and the men easily get Billy away from the stage during a rest stop. Ben meets them at a prearranged location where Sam provides a medical statement that will allow Billy admittance and protection in a state hospital. Ben then reveals that despite his efforts, the citizens of Dodge City learned of Bat’s actions and have voted to strip him of his badge. Bat returns to town where a special election is called. Howard expresses dismay that Bat has broken his oath and Bat is surprised at the depth of his own disappointment. When Bat goes to Pauline to tell her he plans to turn himself in, she remains disdainful and aloof. Realizing his attraction to her has been only superficial, Bat departs and goes in search of Sam at the Lady Gay. Lily welcomes Bat back with enthusiasm, which is cut short when Regan summons Bat into the street for a show-down. Despite Sam and Lily’s warnings, Bat meets Regan and offers to wage their battle at the election box, but Regan refuses. Regan draws, but Bat kills him. Declaring that the “election” has been decided, the town committee agrees that Bat remain sheriff and he returns to Lily, Sam and the Lady Gay.