In German-occupied France, archaeologist Professor Bresson entrusts his heavily trapped diary and an amulet containing the key to the book to his family. The diary is said to be the guide to the “Eclipse,” a treasure hungrily sought by a Nazi faction within Ahnenerbe. When German soldiers arrive, Bresson is killed and his family flees, only to be pursued by Ahnenerbe professor Lambert. A car crash leaves the infant daughter as the sole survivor, while Lambert seizes the amulet and the diary is lost in the chaos.
Decades later, in the 1960s, the diary resurfaces during a memorial exhibit honoring Bresson. The notorious thief Arsène Lupin III makes a bold bid to steal the book, echoing a failed attempt by his grandfather. Lupin’s efforts are thwarted first by a young woman disguised as a security guard, then by Fujiko Mine, and eventually he falls into Inspector Zenigata’s custody. On the way to prison, Lupin is sprung by his allies, Daisuke Namikawa as Goemon Ishikawa XIII and Kiyoshi Kobayashi as Daisuke Jigen, and they infiltrate the home of the fake guard, the archeology student Laëtitia Lambert. Lupin reveals a medal identical to the one Lambert’s grandfather left behind, tying their fates together. Laëtitia contacts her adoptive grandfather Lambert, who directed her to steal the diary in the first place, promising a future scholarship in archaeology if Lupin and the diary can be delivered to him.
Meanwhile, Fujiko Mine secretly hands the diary over to Ahnenerbe fugitives, among them Lambert, who are hunting the Eclipse. Geralt, the other key player among the fugitives, discovers Fujiko’s duplicity and has her detained. Laëtitia guides Lupin to Lambert’s hidden transport-plane stronghold, where the two retrieve the diary and Lupin’s matching amulet’s counterpart. Opening the diary, Lupin and Laëtitia learn that the Eclipse is a power generator left by an advanced civilization and hidden within the ruins of Teotihuacan. The two realize Lambert and Geralt intend to use the Eclipse to resurrect the Third Reich and reshape history.
Lambert, meeting Laëtitia’s unanticipated knowledge of the plan, manipulates the situation to force Lupin into a trap, and Lupin surrenders to Geralt and Lambert. Fujiko uses Lupin as a diversion to escape, while Lupin secretly returns to the plane to listen in on Geralt and Lambert. They reveal a plot to locate Adolf Hitler, who supposedly faked his death and fled to South America, intending to use the Eclipse to restore the Nazi regime. Laëtitia overhears and confronts them, only to be flung from the plane by Geralt. Lupin retrieves the diary and amulets, and the two are rescued by Fujiko, Jigen, and Goemon. Left stranded, Lupin entices Zenigata by radio to his location, snatching an Interpol helicopter and drawing on Zenigata’s help to mount a joint rescue mission with Laëtitia.
Over a stop, Lupin explains to Laëtitia that she is Bresson’s granddaughter, and that Lambert adopted her solely to obtain the diary and the Eclipse. He also uncovers that his own grandfather once aided Bresson in locating the Eclipse before ultimately sealing the book away to prevent it from falling into the wrong hands.
Geralt and Lambert reach Teotihuacan’s hidden sanctuary, but without the diary their progress falters, forcing a retreat. Lupin’s team capitalizes on their absence to navigate past the traps, only to discover the retreat was a ruse designed to clear a path to the Eclipse. As Lambert and Geralt trigger the device, the Eclipse whisks them both to the surface with Laëtitia in tow, but Lupin’s crew intercepts them before escape. Lambert, determined to claim the power, reactivates the plane and triggers a micro black hole to finish Lupin’s team. He dies heroically after taking a bullet meant for Laëtitia, and Geralt receives news that Hitler has been located, taking the Eclipse and Laëtitia to his side.
Arriving at the Ahnenerbe headquarters, Geralt meets Hitler and heads off in the Eclipse to test its capabilities. Left behind, Laëtitia discovers that Lupin’s gang has reached the base with Zenigata’s Interpol team. Lupin disguises himself as Hitler, and on the Eclipse he reveals his true plan. He tinkers with the controls to release a micro black hole inside the device, sucking Geralt into the void and forcing Lupin to flee with the gravity device that Laëtitia had earned and a promise of Boston enrollment.
In the end, the story blends danger, clever wit, and the push-pull of loyalty as Lupin and his companions evade capture while Laëtitia’s future is secured—thanks to Lupin’s final choice to keep her safe and headed toward a new life in Boston.
