1. Venice at night. Menuzzi is planning an attack on Casanova, a renowned gambler and seducer of the city’s noble women and wives. Hohenfels, an officer in the service of the Austrian empress Maria Theresia, interferes. He is on a secret date with Laura, who is due to leave for Spain to join a convent against her will. Hohenfels promises to free her. Casanova’s heart is set on dancer Barbarina, who has an engagement at the local theatre.
2. At the Teatro San Samuele, a Prussian ambassador, Dohna, his wife Helene and her maid Trude meet Count Waldstein, a great admirer of Barbarina. Casanova arranges a private meeting with Helene, who engages him to teach Prussian cadets the rules of chivalry. He agrees to follow her to Potsdam. Meanwhile, his “Leporello” Costa has his eyes on Trude. Dohna announces that Waldstein and he are to bring Barbarina to Frederick the Great, King of Prussia, as a diplomatic “gift” from the empress. Hohenfels, who is reporting to Waldstein, is to join the convoy. Casanova offers his lifesaver to free Laura from the convent in his place.
3. Upon their arrival in Tarragona, Spain, Casanova enjoys an encounter with dancer Dolores, who reads his palms – with worrying predictions: his life will end in great loneliness. Casanova hires Dolores to inform Laura of his coming and seizes the incoming toreros’ parade to facilitate her escape moments before she is due to take her vows.
4. In Vienna, the opera ball is in full swing. Dohna and Helene, stopping over on their way to Potsdam, are among the guests, as are Waldstein and Barbarina. Helena is eagerly awaiting Casanova, who arrives with Laura. When reunited with Hohenfels, Laura startles the officer when singing Casanovas’ praises. He, however, only seems to have eyes for a mysterious beauty. When Casanova finds himself at the centre of female attention, the unknown woman reveals her identity – the empress – and orders the “chastity commission” to imprison Laura. Casanova arranges for Trude to swap clothes with Laura. Trude is arrested while Casanova manages to escape with Laura.
5. Casanova begins his tenure with the Prussian military in Potsdam. Costa is back from Venice where he was unable to deliver a letter from Casanova to Hohenfels, who is away in a military manoeuvre. Casanova decides to dress Laura as a soldier and escort her back to Italy.
6. Casanova and Laura stop over at Count Waldstein’s Duchcov Castle in Bohemia. Waldstein sees through Laura’s disguise at once but offers to help their quest to reunite the couple: he will arrange for Hohenfels to be sent back to Venice and offers to take Laura to meet him personally. If Casanova returned to his home city, he would face trial and imprisonment. Casanova and Laura hesitantly agree to his plan and – with heavy hearts – say their goodbyes.
7. It’s carnival-time in Venice! Casanova has secretly entered the city and observes Hohenfels publically accusing him of having betrayed his trust. When Waldstein arrives with Laura, there’s a happy ending for Hohenfels but Casanova must conclude that he has lost his one real love … or has he?