After masked bandits hold up a stage enroute to Tombstone, Arizona, the third daring crime to be committed in one week early in June 1890, banker George Reid accuses his partner, Mayor Ben Melton, of backing the outlaws and rustlers perpetrating the crimes. That night, Melton murders Reid. Following the robbery of a stage carrying Jewish shopkeeper David Ruskin, Michael Wyatt, who plans to stay in Tombstone only overnight, and Reid's daughter Mary, the three travelers arrive in Tombstone. After Michael shoots the gun out of the hand of drunken Ben Murchison, who has been shooting up the saloon, Melton offers Michael the job of marshal. Because of Mary, Michael accepts. When "Doc" Warren, known as the "coldest-bloodest" killer in the Southwest, tries to provoke a fight with Michael in the saloon, Michael stands up to him, whereupon Doc, who supposedly has no respect for life because he knows he will die soon from heart trouble, buys him a drink. To get information about Melton, Michael visits saloon singer Queenie La Verne, who makes no secret of her desire for him. In her room, Queenie, after unsuccessfully trying to seduce Michael, tells him that she has suspicions about Melton. As the town holds a baby contest to raise money for a school fund, Murchison breaks out of jail. In the dead jailer's hand, Michael finds Melton's watch fob. When Michael helps Doc after a man tries to shoot him, Doc gives Michael a letter that proves Melton killed Reid. Michael, who earlier warned Melton that he had a clue that would lead to the jailer's murderer, surprises Melton robbing his own bank and planning to leave town, but Michael is knocked out by one of Melton's men, and Melton retrieves the incriminating watch fob and letter. Melton accuses Michael of trying to rob the bank, and after the town's judge arrests Michael, Doc helps him escape. Michael gets word to David to follow Melton, and David overhears Murchison demand from Melton his cut of the stagecoach holdups and cattle rustlings, and then hears Melton say that Mary is going to Melton's ranch. Michael and Doc hold up the stage carrying Mary, who believes Michael to be a bandit, and take her to Queenie, of whom she has been jealous. Michael and Doc then engage in a gunfight with Murchison and his men, who are waiting to hold up the stage so that they can capture Mary. After Michael kills all but Murchison, he subdues Murchison and then convinces him that Melton tipped him off about the stagecoach robbery to get him out of the way. Murchison vows to testify against Melton. Meanwhile in town, a lynch mob forms to capture Michael. He gets Murchison into jail through the back entrance, and then, facing the crowd with a rifle, demands a chance to prove his innocence. Learning that Mary is being kept by Queenie, Melton goes to retrieve her, but Michael arrives with the judge, who says that Murchison has confessed everything. Melton pulls a gun to shoot Michael, but Queenie steps in front of him and takes the bullet. Melton is then shot by Doc as he tries to escape and falls to his death from a window. Queenie asks Michael to kiss her, and he complies as she dies smiling. Afterward, Michael and Mary embrace in the sunset.