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.
Episode 1
The Boy Detectives' Club searches for answers when a security robot goes on a rampage in Shibuya in the year 203X.
Episode 2
A young woman approaches the Boy Detectives' Club and asks them to find the intended recipient of a series of threat letters her boyfriend made.
Episode 3
Kobayashi somehow feels that maybe he can die if he stays with Hanasaki, so he joins the Boy Detectives' Club.
Episode 4
After school, Inoue watches Katsuta's tennis club practise before heading home, and Hanasaki tests out some tools of the Boy Detectives' Club trade.
Episode 5
kobayashi and Inoue are trapped in the underground channels as a result of Twenty Faces' manoeuvring.
Episode 6
Hanasaki has been trying to help Kobayashi die, but nothing has worked; while Akechi is away, Hanasaki takes the liberty of accepting six job requests.
Episode 7
Akechi is relaxing at a spa to relieve the exhaustion of his recent cases; Nakamura asks him about his history with Twenty Faces, and Akechi recounts the trauma of his youth
Episode 8
The residents of the Kokorogaoka Housing Complex refuse to vacate their homes for the sake of urban development, so they declare its independence from Japan as an autonomous borough.
Episode 9
Isuzu negotiates with the police for three billion yen in exchange for the removal of the residents of the housing complex.
Episode 10
Hanasaki flees the office after an argument with Akechi and the others; after, Twenty Faces makes an appearance.
Episode 11
Hanasaki's act is successful in convincing Akechi and the Boy Detectives' Club that he was kidnapped by Twenty Faces.
Episode 12
Hanasaki is brought to tears by the conversation between Twenty Faces and Akechi, even with a gun pointed at him.
Episode 13
With the Le Waqua incident resolved and Twenty Faces in custody, the world appeared to be at peace again but the trauma of the incident left Hanasaki psychologically unstable
Episode 14
Yamane Tasuku, a member of the Scientific Experiments Club, is troubled by three things: Ohtomo picks on him, he's always left behind in conversations, and he doesn't know how to become a member of the Boy Detectives' Club.
Episode 15
After being out of touch for so long, Akechi calls the office; the Boy Detectives' Club receives an odd request.
Episode 16
To escape the enemies targeting Fukiya, the death row prisoner they're guarding, the Boy Detectives' Club takes refuge in the abandoned building that Kobayashi had once been using as his base
Episode 17
Inoue and the other detectives are disheartened after being told that the Boy Detectives' Club would be disbanded; the strange air around Kobayashi has returned and is working hard to heal his wound.
Episode 18
Inoue and the other detectives are disheartened after being told that the Boy Detectives' Club would be disbanded; the strange air around Kobayashi has returned and is working hard to heal his wound
Episode 19
As he's resting to recover from his gunshot wound, Kobayashi has an odd dream in which he sees a woman in a bed and a man approaching her; he doesn't recognize them, but the dream gives him a strange headache.
Episode 20
Kobayashi searches for the place that he saw in his dream; Hanasaki and Hide-chan then show up and offer to help.
Episode 21
Miyanishi was shot to death by Nakamura; during her interrogation, Nakamura testifies that Twenty Faces is actually Akechi.
Episode 22
Akechi, stunned to learn that Nakamura was brainwashed by Twenty Faces, ends up captured by the special security force. Meanwhile, at the New Tokyo World Fair, the plane built to carry people to the stratosphere is involved in a catastrophic crash
Episode 23
The Boy Detectives' Club arrives at the Space Expo; Hanasaki and Kobayashi board the shuttle for Twenty Faces' base, where Akechi is being held captive, but things don't go as planned.
Episode 24
Hanasaki left Kobayashi behind and took off for Twenty Faces' hideout alone, planning to put an end to everything; Kobayashi can't accept that, so he follows him even though the aura surrounding him has already disappeared.
