 Inspector Clouseau is assigned to guard a large diamond, the De Gaulle Stone, from theft, but a three-headed villain in a black coat promptly takes it from him. Clouseau and Sergeant Deux-Deux track the three-headed thief to his hideout, where the thief has secreted the jewel in a glass of water. While searching the premises, Clouseau finds the glass, drinks its contents (jewel included), and is rushed to surgery. Doctors remove "a very expensive-looking gallstone" and give it to a nurse, who is the three-headed thief in disguise!