Castle Dux, Bohemia, 1798. Casanova, now a penniless librarian in his seventies, begins to tell his life story to Edith, a young kitchen maid in the castle he works in. We return to Casanova's childhood and humble beginnings as the son of an actor in Venice. As a young man he studies for the priesthood, but is expelled from his seminary, then meets and falls in love with Henriette... but the Duke of Grimani wants Henriette for himself.

Casanova, living on his wits and as a mystic, does a good deed and comes into a fortune. Bragadin offers to adopt him and Henriette agrees to marry him. Grimani, enraged, has Casanova arrested and charged with witchcraft, but he escapes from prison and flees Venice - taking with him Jack, his young illegitimate son by a previous liaison, and Rocco, his servant. Casanova heads for Paris, as he knows that Venetian ambassadors abroad are able to grant pardons.

In the past, we follow Casanova's adventures in London - where he glimpses Henriette and tricks his way into court circles - and in Naples, where he meets an old friend. Still living on his wits, Casanova makes and loses fortunes and also enjoys other conquests. Back in the present, Edith realizes that Casanova may be wrong in believing Henriette is dead. But Casanova himself is now very sick and getting near his end.