His Aunt Sophie (Helen Westley) and his teacher Professor Heinrich (Jean Hersholt) are sure that Roger Grant (Tyrone Power) will be a famous classical violinist, but Roger's more interested in popular music. He and his friend, pianist Charlie (Don Ameche), audition at a saloon in San Francisco's Barbary Coast, using sheet music left by singer Stella Kirby (Alice Faye), which had been sent to her by a friend in New York, Irving Berlin. The number, "Alexander's Ragtime Band," proves to be a sensation, and Stella goes along with Charlie's plea to sing with the band, which soon becomes famous for its ragtime numbers. Charlie has fallen in love with Stella by the time they open at the Cliff House, but he soon realizes that she and Roger are in love. Stella is invited to New York by a famous producer, but Roger's against this, and angrily fires her, so Charlie quits, too. When Roger returns from World War I, he meets Stella, only to learn she and Charlie have been married for a year. Another year passes, and Charlie and Davey have formed a new band with Jerry Allen (Ethel Merman) as their lead singer. Charlie knows Stella still loves Roger, so he divorces her, but Roger sails for Europe with the new band. Back in New York, Roger is set for a major concert in swing at Carnegie Hall. Charlie tells Roger about the divorce, and that Stella still loves him. Unable to get a ticket, Stella listens to the concert in a cab. Explaining that he is playing it for one particular person, Roger and his band perform "Alexander's Ragtime Band" as their encore, bringing Stella into the theater, where she's reconciled with Roger. He brings her onstage to perform the number with his band.
~ Bill Warren, All Movie Guide