Venice, 1755. Giacomo Casanova, just returned from exile in Vienna, threatens to kill hearts and create havoc in the city with his unparalleled charisma. Meanwhile, the Doge Francesco Loredan is in poor health and the Inquisitor Pietro Garzoni plots to influence in his favor the succession to the Dogado. In this regard, the latter intends to get rid of Casanova, because it could ruin his plans, and to the purpose he entrusts the evil Zago. While at Cantina do Mori, the Prince of Seductors meets an old flame: the beautiful Gretchen, who leads him to the palace of Countess Margarethe von Steinberg, for whom she works as a waitress. Here, Casanova meets the great lady and is challenged by her in a singular bet: if he succeeds in seducing the young Francesca Erizzo, daughter of one of the elders of the city, she - Margarethe - will be his for one night.