Kogorou Akechi is the founder of a private investigation firm known as the Boy Detectives' Club. Together, this group takes on cases both great and small. One of their junior members, Kensuke Hanasaki, is out solving a case one day when he happens upon Yoshio Kobayashi, a mysterious amnesiac boy with an inability to die. After seeing his abilities in action, Kensuke offers Yoshio a deal: join the Boy Detectives' Club...