On New Year's Eve, 1905, saloon keeper Blackie Norton hires Mary Blake to sing in his Paradise Club on Pacific Street in San Francisco's Barbary Coast. Mary becomes the Paradise's star, especially for her signature tune, San Francisco.
Blackie decides to run for the San Francisco Board of Supervisors at the behest of his childhood friend Father Tim Mullin, who believes Blackie can use the supervisor position to implement reform.
Mary is hired by the Tivoli Opera House on Market Street, where she becomes involved with Nob Hill scion Jack Burley. After her performance one night, Blackie visits Mary in her dressing room. Realizing she still loves him, Mary asks him to marry her. Blackie agrees, but their reunion is soon interrupted by Burley, who had proposed to Mary prior to the show. Burley appeals to Mary, but Blackie presents Mary with an ultimatum by asking if she wants to marry him or stay at the Tivoli. Mary chooses to return to the Paradise.
Backstage on the opening night of her return performance, Father Tim drops in and is angered by Mary's skimpy stage costume. He defies Blackie to put her on the stage in front of the rowdy Paradise audience. Mary decides to leave with the priest after Blackie strikes him in the face.
Mary goes back to Burley and meets his mother at her Nob Hill mansion. Mrs. Burley tells Mary that she had a "Blackie" in her younger days, but chose to marry the more steadfast Burley. This cements Mary's decision to accept Burley's proposal.
On the evening of April 17, 1906, Burley has the San Francisco Police Department raid the Paradise. Blackie, distraught about the future of his club, ends up at the city's annual Chickens Ball. After performances by acts from the other clubs, the MC requests the Paradise's entry. When no one steps on stage, Mary, just having learned of the club's closing, enters the competition on behalf of the Paradise. She rouses the audience to join in a chorus of San Francisco and wins, but Blackie refuses the prize money and states that Mary had no right to sing on behalf of his club. Mary is about to leave the ball with Burley when the earthquake hits the city.
As Blackie wanders the devastated city searching for Mary, he finds Burley dead and Mrs. Burley distraught. The police begin dynamiting buildings in order to control the fires. Blackie also comes upon a dying Mat, who tells Blackie he was wrong about Mary. Blackie later meets Father Tim, who takes him to a homeless camp in Golden Gate Park. Blackie hears Mary singing Nearer, My God, to Thee with those in mourning. As they reunite, word spreads through the camp that "The fire's out!" As people shout about building a new San Francisco, Blackie and Mary join the crowd as they leave the park marching arm-in-arm, singing The Battle Hymn of the Republic.
