Arsène Lupin, disguised as Raoul d'Andrézy, travels to Vienna to attend a conference on treasures. At the home of wealthy Baron Ordosczy, the conference begins. Corcoran explains that the mysterious inscriptions engraved on 7 rings conceal the secret of Cagliostro's treasure. The light goes out. When it returns, the rings have disappeared.

Following a car accident, Arsène Lupin finds himself in a Vienna hospital. Now completely amnesic, he is cared for by a beautiful nurse. And Inspector Pittora reveals that when he was found wandering alone in the countryside, he was carrying four passports, all valid, and a large sum of counterfeit money. Grognard, Lupin's loyal valet-driver, was found wounded near the car, taken to another hospital and unaware of his boss's whereabouts.