The young detective Club in the company of Dr. Agasa went Okayama prefecture to visit the museum. Later, they found a group of guys, childhood friends, who gathered to celebrate the marriage of two of them. The Detective Boys noticed a container floating in the water and discover that inside is a secret message. Fairly and finely, Conan decipher the meaning of the code that refers to another container. The Detective Boys then undertake a kind of treasure hunt that stops abruptly when Ayumi recovers the body of one of the group next to one of the places where there was a time capsule of the club.