Infamous womanizer Casanova (Heath Ledger) finds himself in an unfamiliar position, that of pursuing a monogamous love affair with a woman, after meeting Francesca Bruni (Sienna Miller). When he discovers that Francesca is, in fact, publishing feminist writings under an assumed name, he knows his attempts to win her will be rebuffed if she knows his true identity. This begins a farce of mistaken identities and betrothals, all devised by the reforming lothario himself as he manipulates most of Venice in an attempt to win the girl who has stolen his heart. This would be a difficult enough task if he did not also have to dodge Pucci, the Vatican's inquisitor (Jeremy Irons), who has set his mind on the apprehension and prosecution of Casanova.