Unlike the original "The Boy Detective Club" series told in the Showa era of Japan, the anime is set in the future, in the year 203X. 15-year-old Kensuke Hanasaki, a member of the Boy Detectives Club led by private detective Kogoro Akechi, one day meets a boy named Yoshio Kobayashi. The 14-year-old boy has become immortal after being haunted by a mystrious mist. He yearns for death, and shirks from contact with other people. Hanasaki becomes interested in him and asks him to join the club. Their encounter gradually leads them to become involved in a grudge between the greatest criminal, the Fiend with Twenty Faces, and detective Kogorou Akechi.