After being fired from a nuclear research project on Pearl Island, Jim Lorman steals the project's only -- and very valuable, research fish. Meanwhile, Sandy and Bud arrive on the island for a tour. The research fish is then discovered missing and Flipper is believed to have eaten it! The dissecting room is prepared to retrieve the specimen. The boys are distraught and leave to find their father. They come upon Jim Lorman and discover the specimen on his boat. Sandy escapes while Lorman holds Bud captive. Sandy finds his father and tells him of Lorman's treachery. Together they capture Lorman and release Bud. The Ricks arrive at Pearl Island with the missing fish just in time to save Flipper's life.