The aging Casanova recounts his unhappy childhood, his forays into Venetian society and his meeting with Henriette, the love of his life.

The aging Casanova (Peter O'Toole) is eking out a living as librarian to an absentee count. Encouraged by Edith (Rose Byrne), an innocent but curious servant, he begins reading extracts from his salacious memoirs. We learn of his unhappy childhood, his sexual awakening and the adult Casanova's (David Tennant) modus operandi in Venetian high society, where he acquires a servant, Rocco (Shaun Parkes), and impersonates the ways of the wellborn in order to acquire money and seduce women. He meets an equally canny and upwardly mobile female version of himself in Henriette (Laura Fraser), with whom he falls madly in love. But she is engaged to Grimani (Rupert Penry-Jones), a jealous and conceited member of the nobility. While pursuing the seducer's art, Casanova becomes intrigued by Bellino (Nina Sosanya), a castrato whom Casanova is convinced is really a woman. He proposes; however his more lasting attachments have a way of not working out. While hearing Casanova's confession, a priest collapses from sin overload. Casanova nurses the cleric, Bragadin (Freddie Jones), back to health and is rewarded handsomely. Convinced that Henriette can now afford to ditch Grimani for him, our hero makes his move.