The parents of young Justus were both scientists studying nature and the environment. They had been away all year round, but were later unfortunately killed during an expedition. The only thing left behind was a video tape they recorded before their death, indicating that the incident was related to a weird castle. In order to find out the truth of the matter, Justus and his two little friends Mouse formed a detective organization. They used the prize money Justus received in a competition to start their expedition. After deciphering the hints left by their parents, they finally found this mysterious castle, and then encountered many strange people and strange things here.