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...
is find out who these 
letters are intended for,
wer das Ziel der Briefe sein soll
es descubrir a quién
están dirigidas estas cartas
é descobrir para quem ele escreve isso