The famous swindler Arsène Lupin III dashingly pulls off a grand theft of millions of dollars, after which he learns that the booty in his hands - the most skillful forgery. It was created in the European principality of Cagliostro, the rulers of which for many centuries traded in the production of counterfeit bills. Unaccustomed to losing, Lupin heads to the castle of the Princes of Cagliostro, but the search for money is put on the back burner when he meets the charming Princess Clarisse.