In the town of Abilene, Mayor Oliver visits the Dry Gulch Saloon and asks the owner, Theodore "Theo" Rush," to take down the poster of Billy Coe. Coe, a reputed rustler, just lost the election against Oliver. She refuses to take down the poster and Oliver appeals to the marshal, Heck Thomas. Marshal Thomas is playing poker against Bart and winning. While Bart tries to get someone to extend him a line of credit, Marshal Thomas tells Oliver that Theo isn't doing anything illegal and he just wants a peaceful town until Wyatt Earp arrives to replace him so he can retire.
As Bart puts his watch up as collateral, a gunman opens fire on Marshal Thomas, killing him. Bart draws and kills the gunman, who the townspeople confirm is The Beasley Kid. They figure that Beasley was working for Billy. They turn to Bart and ask him to serve as marshal until Earp arrives in town. Bart only wants to collect his poker winnings since he figures the pot is his now that the marshal is dead. Mayor Oliver refuses to let him pick it up unless he accepts the job and threatens Bart with a vagrancy charge if he has no money. Bart gives in and accepts the offer, only to discover that the marshal had the winning hand anyway. He tries to round up a posse to go after Billy but the townspeople will have nothing to do with him. Bart figures that Billy will have to come into town and Earp will deal with the rustler when he arrives. However, Theo explains that Earp won't arrive in Abilene for six weeks.
Later, Bart gets word that Billy is in town at the Dry Gulch. Theo is with her lover, Billy, and he says that he plans to make a fortune and provide for her. She tells him that she won't have him win her that way and she wants him to become mayor and come to power legitimately. Billy refuses and leaves the upstairs office and finds Bart waiting for him. Bart suggests that Billy leave town for six weeks. Otherwise he'll have to come after Billy himself and there's no profit in either one of them getting killed. Once Earp is there, Billy can deal with him. Billy insists on staying in Abilene and Bart tells him that Beasley signed a confession before he died. The rustler draws a gun on him and forces Bart to take him to the confession. However, Theo comes up behind them and draws on Billy, forcing him to leave. Once he's gone, Theo reminds Bart that Beasley died instantly. He agrees but notes that now they know that Billy hired Beasley to kill the marshal. Theo sheepishly admits that she backed her lover and let her feelings get in the way.
Word travels fast and Mayor Oliver comes to see Bart and demands that he arrest Billy. When he wonders why Bart didn't arrest him at the Dry Gulch, Bart points out that he didn't know who Theo would side with. The mayor threatens to fire him for incompetence and Bart eagerly resigns. However, as he heads for the stagecoach, a tall man with a mustache and sideburns gets out. Bart and the mayor recognize the one-of-a-kind Buntline Special that the newcomer is wearing, a gun that belongs to Wyatt Earp. The man admits that he is Wyatt Earp and that he arrived in town early. When they tell him that Marshal Thomas was gunned down, he starts to leave. However, when they tell him that Bart dispatched Beasley and has been serving as Marshal, Wyatt decides to stay after all. The first thing he does is deputize a reluctant Bart and threatens to shoot him down if he doesn't accept.
Later, Wyatt visits Bart at his hotel room and discovers that he's packing to leave town. Bart figures that Wyatt won't shoot him if he doesn't shoot first. Wyatt agrees to let Bart go but talks about how his brothers Doc Holiday and Bat Masterson are all tied up elsewhere and he'll have to take on Billy and his gang alone. He keeps pouring it on until a guilty Bart agrees to help him. Wyatt then borrows his $20 gold piece and goes down to play poker, promising to pay Bart half of his winnings.
Wyatt is soon winning big at the poker table while an admiring Theo watches him. Bart watches as Wyatt bets high, tosses away one of two aces, and draws to an inside straight. Unable to take the strain, Bart goes outside for some fresh air. Wyatt comes out after him and gives him half of his winnings and the gold piece. They patrol the town and talk about Billy and Wyatt says that Bart can handle the rustler. They split up and Wyatt practices drawing the long-barreled Buntline. However, he's unable to even get it clear of the holster.
Billy and his men ride into town and spot Wyatt. As Wyatt yells for Maverick, Billy tells him to draw. Wyatt trips and rolls across the street as Billy shoots and misses. Bart arrives and returns fire and Wyatt manages to fire his gun…at Bart. He shoots off Bart's hat and manages to hit one of Billy's men lurking on a balcony. Mayor Oliver sees the whole thing from the saloon door. Bart fires back and drives off Billy and his men. As they ride out of town, the townspeople come out to congratulate Wyatt and Bart. Wyatt has no idea that he killed a man and tries to give Bart all the credit. Mayor Oliver and Theo insist on recognizing Wyatt and take him into the saloon, while Bart tries to work out how Wyatt shot his hat off and hit the man on the roof.
At his hideout, Billy receives word from George, the Dry Gulch bartender, that Wyatt is planning on calling in his brothers for help. Worse, George tells Billy that Theo is sweet on Wyatt. Billy sends George back with a message for Theo to invite Wyatt to breakfast or she gets a bullet. As Theo considers the idea, Wyatt arrives at her doorstep and invites her downstairs for coffee. She invites him in while George goes outside and tells Billy's man that Wyatt is in position.
Wyatt starts to tell Theo something important and she tries to tell him that it's a trap. However, Billy's poised killer climbs up on the balcony and prepares to throw a knife at Wyatt. Theo sees him and throws herself on Wyatt to protect him. While the killer tries to get a clear shot, Wyatt assumes that Theo is trying to embrace him. He finally sees the killer and runs down to the street, screaming that Billy is coming. Everyone panics and runs inside as Billy and his men ride up. Billy realizes that Theo double-crossed him and prepares to kill Wyatt. Bart hears the noise and runs outside to investigate. The rooftop killer tries to throw a knife at him but Wyatt accidentally shoots off Bart's hat and kills the man. Billy shoots the Buntline out of Wyatt's hand and the marshal runs to the saloon and hides behind Theo. Billy boasts that he'll kill Wyatt at 3 o'clock that afternoon using his own gun and rides out of town. Mayor Oliver congratulates Wyatt on his miraculous shot but Wyatt gives Bart the credit and suggests he shoot it out with Billy at 3. Bart refuses, saying that as marshal, Wyatt will have to deal with the rustler.
Later at the marshal's office, Earp is desperately practicing with a new gun when he and Bart get a visitor: the real Wyatt Earp. He's heard about someone pretending to be him and the imposter admits that he borrowed Earp's Buntline and Billy took it. They demand an explanation and the imposter explains that he's Archibald Walker, a bartender from Laramie. He was tending bar when Earp received a telegram offering him the Abilene job and his reply that he would be there in six weeks. Archie "borrowed" Earp's Buntline and came to Abilene to impersonate him. When they wonder why, Archie explains that all of his life he has been a nobody and he wanted to be someone who was loved and feared and respected. He got that when he pretended to be Wyatt and that he's lived more in the last six weeks than he has his entire life. Earp figures that he'll have to take on Billy without his fabled Buntline and Archie insists on finishing what he started. Bart and Earp refuse and Bart promises to get Archie out of town on the next stagecoach. Earp agrees as long as Bart has the barber trim off Archie's mustache and sideburns.
Bart goes on to the barbershop while Archie goes to see Theo. He tells her the truth and admits that he's leaving town and she wonders if he's going to abandon her to Billy. Archie says that he doesn't have a choice and goes to the barbershop. The barber, Elkins, still believes that he's Wyatt. They tell him that Archie isn't Wyatt and that he's to tell no one. As Bart leaves to get the stagecoach ticket, he runs into his old friend, Doc Holliday. Holliday is stopping over at Abilene for a shave and a bath and to duck a young girl named Cassie Jones who wants to marry him. He asks Bart to tell her that he's already left town and Bart agrees to help his friend. As Holliday goes to the bath, Archie gets an idea and tells Elkins to trim his mustache to look like Holliday's.
Three o'clock arrives and the bartender tells Billy that Holliday has arrived in town to back Earp. As the townspeople run for cover yet again, Archie steps out... dressed as Doc Holliday. When Mayor Oliver goes to the marshal's office to get "Wyatt," he has no idea who the real Earp is. Earp prepares to take on Billy, but Archie holds him at gunpoint and locks him in the marshal's office.
Archie walks out onto the street to confront Billy. Bart sees the showdown from his hotel room and runs out to help. He bumps into Theo, who says that she loves Archie. As Bart comes out, he spots one of Billy's men on a roof. He shoots from the ground, knocks off Archie's hat for once, and nails the killer. Archie and Billy draw but Billy is the one who can't get his gun out of his holster. He pulls the trigger, shooting the ground, and Archie thinks that he's been hit. He fires and kills Billy. Bart comes over and assures him that he's fine and the townspeople come over to congratulate "Doc," who they realize is "Wyatt," who finally admits that he's Archie. Doc Holliday comes over from the baths and demands that Archie give him his stolen clothing.
Later, everyone gathers at the stagecoach station to wish Archie well. Unfortunately for Holliday, Cassie has caught up with him. Archie promises Holliday and Earp that he'll never impersonate them again. Theo is relieved that Archie is alive and promises to sell the saloon and move in with him once he gets back to Laramie. The stagecoach leaves and Bart offers Holliday and Earp a game of poker. However, he realizes that his deck is gone.
On the stagecoach, Archie informs his fellow passengers that he is Bart Maverick and offers to play a game of poker with them.