Riverboat entertainers find love, laughs and hardships as they sail along "Old Man River."

Cap'n Andy Hawks's show boat the Cotton Blossom arrives in New Orleans. Andy's daughter Magnolia, a gifted singer, meets Gaylord Ravenal and they make believe they are in love. While rehearsing, 'Nolia's good friend, Julie LaVerne, and her husband, Steve Baker, are accused of miscegenation and are forced to quit the show and leave town. 'Nolia and Gay take their places and, because their romantic involvement onstage mimics their real feelings, they are a hit. Pete Gavanaugh, who caused Julie's ostracism when she refused his advances, then writes to Andy to expose Gay as a murderer who was let off on a verdict of self-defense. After a successful run of their show, Gay and 'Nolia marry with Andy's blessing, even though 'Nolia's mother Parthy objects to the marriage because of Gay's questionable past. A year later, 'Nolia gives birth to Kim during a storm while Gay is away playing cards. Gay returns the next morning and asks 'Nolia to move to Chicago. Initially, the family lives well at the Palmer House while Gay bets on horses, but his money quickly runs out and they are forced to move. When Elly and Frank, former members of the show boat, inquire about a shabby room for rent from which the present tenants are being evicted, they discover the tenants are 'Nolia and Gay. Gay then deserts 'Nolia because he is ashamed that he cannot provide for her and Kim. 'Nolia then performs at the Trocadero after Julie, now an alcoholic, quietly quits so that her old friend 'Nolia can get work. Parthy and Andy then arrive at the Palmer House on New Year's Eve in search of the Ravenals, and Andy discovers 'Nolia singing at the Trocadero. Although the crowd is not receptive to 'Nolia's lyrical voice, Andy gives her support from the audience and she is a success. Soon 'Nolia is an international star. Years pass and she retires from the stage, after which Kim follows in her footsteps. When Kim opens on Broadway, 'Nolia recognizes Gay, who is posing as the stage doorman. After the encore, Kim invites her mother to sing and Gay joins her in song.