The Mystery of Mamo, also known as The Secret of Mamo, is a 1978 Japanese animated science fiction action comedy film; it is the first animated film of the Lupin III franchise created by manga author Monkey Punch. The film was originally released in Japan as Lupin III (ルパン三世, Rupan Sansei) but was later retitled to Lupin III: Lupin vs. the Clone (ルパン三世 ルパンVS複製人間クローン, Rupan Sansei: Rupan tai Kurōn) to differentiate it from other elements of the franchise. Directed by Sōji Yoshikawa from a screenplay by Yoshikawa and cult pink film screenwriter Atsushi Yamatoya, the film was produced by animation studio Tokyo Movie Shinsha and distributed by Toho. The film's plot follows master thief Arsène Lupin III, who attempts to foil Mamo ― a wealthy and powerful recluse seeking immortality ― while trying to win the affections of his rival and would-be lover, Fujiko Mine.

When Brazil's illustrious Santos FC and their American counterparts square off at the world's largest sports arena, Rio de Janeiro's Stadium Maracanan, the box office and betting takes are huge. Thus, Lupin and company plan to take the money, first getting themselves thrown in jail to give themselves alibis, and then escaping to make the theft once this is done. Will things go entirely as planned?

Supposedly, an old man who knows the secret of the legacy of Hitler is living on the other side of the Berlin Wall. Walls are no problem, and taking Genhardt, the old man, to the West is easy enough, but he is absolutely senile and recalls nothing about any legacy. Therefore, the plan is to reenact a scene from the period, but... What has happened to the legacy, anyway?