 Gauche knows that the murderer must be one of the first-class passengers, because one of the special golden badges for the ship's first-class passengers was left in Littleby's room.Among the suspects are a Japanese Army officer, an addled English aristocrat, a married Swiss woman, and a clever young Russian diplomat on his way to his new post in Japan.The diplomat is Erast Fandorin, the master detective, who shoots down each of the ineffectual Gauche's incorrect conclusions, and in the end takes it on himself to find the murderer.