Young Mary Grant (Hayley Mills) and her brother (Keith Hamshere) travel to Scotland with their friend Professor Paganel (Maurice Chevalier) to attempt to convince Lord Glenarvan (Wilfrid Hyde White) to help locate Mary's missing father, Captain Grant (Jack Gwillim). As Grant was working for him, Glenarvan agrees, and the group sails to South America and then Australia in search of him. They eventually meet the treacherous Thomas Ayerton (George Sanders), who may know the captain's location.