A beautiful singer and a battling priest try to reform a Barbary Coast saloon owner in the days before the big earthquake.

In San Francisco, the new year of 1906 is ushered in with a fire along the Barbary Coast, interrupting the revelries of Blackie Norton, owner the the Paradise Cafe, who rushes to the blaze to help. Blackie returns to the Paradise and meets out-of-work singer Mary Blake, the daughter of a country preacher. Although Mary's only experience has been singing in a church choir, Blackie is attracted to her and offers her a two-year contract. Soon after, a citizens' group, angered at the New Year's Eve fire, urges Blackie to run for supervisor on a ticket of reforming the outdated fire ordinances. Blackie, encouraged by his boyhood friend, Father Tim Mullin, accepts the challenge. Blackie's candidacy prompts Jack Burley, a Nob Hill patrician who owns tenements along the Barbary Coast, to visit Blackie and advise him against running for office. Burley, who also owns the Tivoli Opera house, is accompanied by the Tivoli's maestro, Señor Baldini, who hears Mary sing and offers her an audition. Although Mary aspires to be an opera singer, Blackie will not release her from her contract. One night, between shows, Blackie sends Mary to Tim's church to sing at the unveiling of its new organ. Tim tells Mary about his boyhood friendship with Blackie and expresses the hope that some day Blackie will act as a force of good rather than evil. Soon Burley offers to buy Mary's contract, and Blackie leaves the choice to Mary. When, out of loyalty, Mary decides to stay, Blackie responds that he is crazy about her. He then decides to throw a party of celebrate their new relationship, but she soon realizes that she is just another conquest to him and leaves for the Tivoli. Some time later, on Mary's opening night at the Tivoli, Burley proposes, but she does not accept. Meanwhile, Blackie enters the opera house accompanied by a process server whom Blackie has brought to enforce Mary's contract. During the opera, however, Blackie is so moved by Mary's singing that he physically prevents the process server from stopping the performance. After the finale, Blackie visits Mary in her dressing room and she proposes to him. He accepts, but makes it contingent upon her return to the Paradise. As Mary soon prepares to go onstage at the Paradise in a revealing new costume, Tim visits and denounces Blackie for exploiting her. When Tim refuses to allow Mary to go onstage, Blackie strikes him, after which Mary quits and leaves with Tim. Mary finally accepts Burley's proposal, after being convinced by his mother that Blackie is not good for her, but Burley, not satisfied with winning Mary, arranges for the Paradise's liquor license to be revoked and Blackie's performers jailed. The raid occurs on the night of the "Chickens Ball," an entertainment competition that Blackie has won every year. With his entertainers jailed, Blackie has no hope of obtaining the prize money that he badly needs to finance his campaign. Blackie is then given another blow when his friend Mat reveals that the citizens group is withdrawing their support because his campaign has become "too personal." When Mary and Burley go to the Chickens Ball, Della Bailey, an old friend of Blackie's, denounces Bailey for closing down the Paradise. Hearing this, Mary announces that she is going to represent the Paradise and sings a crowd-pleasing rendition of "San Francisco." Della sends for Blackie to witness Mary's performance, but just as Mary is proclaimed the winner, Blackie angrily goes onstage and refuses to take the award when she tries to give it to him. Humiliated, Mary prepares to leave with Burley when the ground quakes and the building starts to crumble. Mary and Blackie call to each other, but are separated in the chaos. Within a few moments, San Francisco is destroyed as buildings tumble and streets open-up. When the shaking stops, Blackie pulls himself from the rubble and searches for Mary. After finding Burley's dead body, Blackie goes to the Burley mansion, where Mrs. Burley, who is being evacuated so that her home can be dynamited to stem the tide of fires now raging through the city, tells him that they both need "God's help." Wandering through the desolation of the city, Blackie finally finds Tim, who is comforting the injured. Recognizing Blackie's contrition, Tim then takes Blackie to a refugee camp, where Mary is leading the dispossessed in a hymn. As Blackie kneels down to thank God for finding Mary, she sees him and goes to his side. They are reunited just as word comes that the fires are out. Blackie and Mary then join others marching back to the city singing "Glory, Glory, Hallelujah."