After planning to leak top-secret information from the Soviet Union to Japan printed within a newspaper message, Anton Morozoff is assassinated aboard the Asia Express. His contact, D-Agency's Tazaki, enlists the help of three boys to identify the killer before he escapes the train at Mukden with the intel. It is revealed that the conductor was the assassin and that he was in cahoots with Morozoff's lover, Elena, who did not want to flee to America with him. Rather than turning her over to SMERSH, Tazaki recruits Elena to be a spy for Japan.