Searching for the lost city of Tobanya, Dr. Hayden, his daughter, Leslie and his assistant, Link Simmons, discover their first clue in uncharted waters of the South Pacific. Link and Leslie find a treasure chest amongst the remains of a sunken ship. They bring the treasure on board. Just then they spot a boat approaching. It is Mu-tan and his band of pirates. Dr. Hayden covers the treasure as Mu-tan's boat comes alongside their own.