It is the 2030s. The Boy Detectives Club gathers under Kogorō Akechi, the mysterious detective. The group solves cases great and small using their unique skills. One day, a member of the club, Kensuke Hanazaki, meets the boy Yoshio Kobayashi. Kobayashi's body cannot die due to the effects of the "Unidentifiable Mist," but he yearns for death, and shirks from contact with other people. Taking an interest in him, Hanazaki invites him to join the Boy Detectives Club. Their meeting is connected to the fate tying together Kogorō Akechi, and the era's greatest villain, the Fiend With Twenty Faces..