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. They accept the job and begin to tail her boyfriend.

Kobayashi somehow feels that maybe he can die if he stays with Hanasaki, so he joins the Boy Detectives' Club. His first mission is to help find a jobless young man who's gone missing.

After school, Inoue watches Katsuta's tennis club practice before heading home, and Hanasaki tests out some tools of the Boy Detectives' Club trade. Meanwhile, a police car is found overturned after a crash.

Kobayashi and Inoue are trapped in the underground channels as a result of Twenty Faces' maneuvering. Worried about the officers searching elsewhere in the channels, Inoue tells Kobayashi to escape and warn them that the map they were given is fake.