Plot

Johann Strauss II pursues his passion for waltzes in 1845 Vienna, facing societal resistance. His music gains popularity through opera singers, leading to fame and personal conflicts between his wife and a passionate affair.

In 1845 Vienna, Johann Strauss II (Fernand Gravey) - 'Jonahi' to his friends - would rather write and perform waltzes than anything else, this at a time when a waltz is not considered proper society music. After he is fired from his clerical bank job because of his preoccupation with composing, he decides to follow his passion and form an orchestra. After some famed opera singers, including Carla Donner (Miliza Korjus), hear his music, they expose Johani's music to the masses, to royalty and to music publisher Julius Hofbauer (Hugh Herbert). As such, Johani becomes the toast of Vienna. With his new found musical fame, Johani's life, which includes his work in the European Revolutions, changes. He becomes torn for his love for his loving and faithful wife Poldi Vogelhuber (Luise Rainer) and his more emotionally passionate but somewhat destructive love for Carla Donner, who herself is involved with Count Anton Hohenfried (Lionel Atwill).—Huggo

Johann Strauss II was a gifted amateur composer who worked in a bank. Johann found that he was often distracted by the melodies in his head and would end up writing waltz instead of computing figures on company time. After he got fired, he decided to become a professional composer.

Johann and a group of amateur musicians put together a small orchestra and had their début performance in a casino. It was a huge success, both inside and outside of the casino were filled with people dancing to his waltz. One of those people was Carla Donner - the star of the Imperial Opera.

Carla liked Johann's music and invited him to play in her lover Count Hohenfried's party. Defying social protocols and tradition, Carla sang to Johann's waltz as a common dance hall singer, and Johann became the most sought-after composer. Having negotiated an unprecedented profitable contract with music publisher Hofbauer, Johann married fiancée Poldi and the couple settled down in a big house.

To show his support of the democratic revolution, Johann wrote a march and led the demonstration. Along the way the crowds saw Carla's carriage parked outside the Count's mansion and was about to attack her - the symbol of the corrupted upper-class. Johann came to Carla's rescue and proclaimed her a fellow artist; thus, the Lady Liberty of their demonstration. This saved Carla for the time being, but their luck turned when the military police arrived to break up the demonstration, Johann and Carla were arrested.

They managed to escape but couldn't go home as most streets were barricaded, the cab driver took them to the Vienna Woods to rest for the night. Next morning, on their way back to the city, the various sounds of human and animal activities inspired Johann. Together with Carla and the cab driver, he came up with a melody Carla named "The Tale of the Vienna Woods".

In need of an orchestra collaboration to finish composing this new waltz, they found a country inn that has an orchestra and Johann went to work. Carla didn't go back to the city but stayed with him - the two had fallen in love. But Johann was interrupted by a mob of crowds - the revolution had ended, a new emperor, in support of a constitution, was now in power.

Back to the city, Johann continued to produce beautiful music; while his relationship with Poldi was anything but. Johann had started an affair with Carla, and as the Imperial Opera commission him to write a new opera for Carla, the affair became known to everyone.

Unaware of Johann's infidelity, a socially-awkward Poldi didn't attend the opening night performance. Count Hohenfried paid her a short visit and gave her the cruel news. Poldi took a gun and rushed to the opera house, just in time to see Johann and Carla together, showered with applause and adoration. Realising that she had already lost Johann to Carla, Poldi asked Carla to look after Johann, congratulated him and went home.

As Johann and Carla were about to board the ship heading to Budapest, he found that he couldn't abandon Poldi. He said goodbye to Carla and stayed on the pier for the rest of the night, not wanting to go home. In the morning, the sound of water movements from the boats and the washwomen around him brought back the melody he and Carla came up with in the Vienna Woods.

This time, he finished the waltz and changed the name to "The Blue Danube".