After pulling off a casino heist, Arsène Lupin III finds that the money he stole is actually "Gothic Bills"—extremely well-made counterfeit notes that are impossible to tell apart from real currency. With his partner Daisuke Jigen, Lupin travels to the small country of Cagliostro to find out where the fake money came from. When they get there, they jump into a car chase and rescue Clarisse d' Cagliostro, the daughter of the late Duke d' Cagliostro, who is running from Count Cagliostro's scheme to take over her family's money by forcing her into marriage.
Wanting to help a woman in trouble, Lupin decides to stand by Clarisse. Soon after, Goemon Ishikawa XIII, Fujiko Mine, and Kouichi Zenigata all get pulled into the situation, each for their own reasons. As everyone ends up at Cagliostro Castle, Lupin remembers a visit he made there ten years earlier, and the hidden truths about the castle begin to come out.