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. Meanwhile Kobayashi, after missing his chance to return Hanasaki's dropped wallet, uses it to buy a desperately needed meal. Hanasaki finds out by checking his electronic money usage history, and he convinces Kobayashi to join him on the current investigation in a second attempt to get him to join the club...
You make these things when you don't want 
to leave clues to your identity, right?
Man erstellt die Briefe doch so,
um unerkannt zu bleiben.
Haces estas cosas cuando no quieres
dar pistas sobre tu identidad, ¿cierto?
Faz isso quando não quer mostrar
sua identidade, não é?