In this fictionalized musical about composer Johann Strauss he marries his childhood sweetheart and falls in love with an opera singer.
In 1844 Vienna Johann Strauss (Fernand Gravey) is fired from a bank and calls on Poldi Vogelhuber (Luise Rainer). He gets musicians to play for free at a restaurant. Opera stars Fritz Schiller (George Houston) and Carla Donner (Miliza Korjus) ask them to play more and leave; but people are drawn to listen. They dance to "I'm in Love with Vienna." At the palace of Count Anton Hohenfried (Lionel Atwill) Johann meets music publisher Julius Hofbauer (Hugh Herbert). Carla sings "There'll Come a Time," and alone together they kiss. Anton gives Carla a necklace, but Johann declines his money.
Johann weds Poldi and signs a lucrative contract with Hofbauer for his waltzes. Johann writes a revolutionary march to promote human rights and is arrested with Carla; but they escape in the rain. Their homes are barricaded; so they take a coach to the Vienna woods, where sounds inspire Johann to compose a waltz. Carla is taken as Mrs. Strauss, sings "Tales of the Vienna Woods," and dances with Johann, who kisses her and says he is married. The revolution wins a constitution and a new emperor, Franz Joseph.
While composing a love song Johann is irritated by Poldi, and she tells him not to shout. They announce they are leaving Vienna, and Johann sings "One Day When We Were Young." Carla tells Johann that he has been commissioned to write an opera for her to sing. Johann declines, but Carla has Poldi persuade him. Count Hohenfried tells Poldi that Johann and Carla are infatuated; but Poldi says nothing is wrong. He warns her that Johann will be ruined unless she fights. Poldi takes a pistol to the opera. As the opera ends, Johann tells Carla that he'll go to Budapest with her. Carla tells Poldi that she and Johann love each other. Poldi says that Johann is free. Poldi announces that she is going with Johann. Carla goes alone and says good-bye to Johann. As the boat pulls away, she sings "One Day When We Were Young." Johann sits on the dock at dawn and composes "The Blue Danube." 43 years later Johann with Poldi calls on Emperor Franz Joseph (Henry Hull), who calls him the king of Vienna and shows him the people singing.
This musical implies that in this era dancing to waltz music was as revolutionary as demanding a constitution under a monarch. The romantic triangle is resolved by the mutual tolerance and understanding of the women.