"Lupin III vs. Detective Conan The Movie" is a crossover film that brings together two iconic franchises: the cunning thief Arsène Lupin III and the brilliant young detective Conan Edogawa. The story is set in the fictional European country of Vespania, where a royal jewel known as the Cherry Sapphire is stolen during a public exhibition. The theft is initially blamed on Lupin III, who is notorious for his heists, but he denies involvement and sets out to clear his name. Meanwhile, Conan Edogawa, along with his friends and allies, becomes entangled in the mystery when they are invited to Vespania to investigate the theft.

The narrative unfolds as Lupin III and his team—Daisuke Jigen, Goemon Ishikawa, and Fujiko Mine—pursue the true culprit behind the theft. Their investigation leads them to uncover a deeper conspiracy involving Vespania's royal family, political intrigue, and a shadowy organization. Conan, using his sharp deductive skills, independently begins to piece together the same clues, eventually crossing paths with Lupin. Despite their opposing roles as thief and detective, the two form an uneasy alliance to expose the real mastermind behind the theft and prevent a larger catastrophe.

The film balances action, humor, and mystery, showcasing the distinct personalities of both Lupin III and Conan. Lupin's charm, wit, and daring heist tactics contrast with Conan's methodical and analytical approach to solving crimes. Supporting characters from both series, such as Inspector Zenigata, who relentlessly pursues Lupin, and Conan's allies, including Kogoro Mouri and Ran Mouri, play significant roles in advancing the plot. The dynamic between the two protagonists drives the story, blending the lighthearted tone of "Lupin III" with the suspenseful mystery elements of "Detective Conan."

As the investigation progresses, the stakes escalate, culminating in a high-stakes confrontation that tests the ingenuity and resourcefulness of both Lupin and Conan. The film concludes with the resolution of the central mystery, the restoration of order in Vespania, and a mutual respect between the two protagonists, despite their differing moral codes. The crossover successfully integrates the unique strengths of both franchises, delivering a cohesive and entertaining narrative that appeals to fans of both series.