"Mr. Otani might remember something." Takagi (Mamiya Shotaro), Koyama (Morimoto Shintaro), and Hatachi (Mori Yusaku) become the targets of a serial murder case targeting their classmates. Unable to figure out who is holding them hostage, the three seek help from their former homeroom teacher, Otani (Akama Mariko), and rush to their alma mater with Sonoko (Araki Yuko). Unfortunately, Otani says he has no idea what's going on. However, Takagi and the others find a clue...