Thomas Gustav, a genius chess player from country S defected to the West with his wife Ingrid some years ago, but he is now suspected of being a spy. Mylene is sent to investigate and pretends to be a runaway girl named Eileen. She befriends a young boy called Billy, who lives in a military port town with his drunkard grandfather Bart. She learns that Billy’s adopted mother regularly visits with presents of boats which Billy sets off from the harbour. Mylene discovers that the boats contain tracking transmitters. The woman is in fact Ingrid, and she has been using the toy boats to send messages to the Eastern Bloc.