Yako receives tickets to an onsen. During the trip Neuro, Yako and Godai meet a group of college students, one of whom is an American exchange student. The American attracts the others' attention by knocking at the door of a closed room, and Neuro, Yako, Godai, and the students find a girl and poison gas in the room. The apparent suicide is really a murder, committed by the rebuffed American student.