: To return the stolen diamond, the country's government turns to Sherlock Holmes, and he deftly deceives the scammers who stole the stone.

Representatives of the government of the country turn to the great detective Sherlock Holmes with a request to find the stolen diamond, known as the “Mazarini Stone”. The Prime Minister and the Minister of the Interior hope for success, while Lord Cantlemere doubts the possibilities of a great detective.

After conducting an investigation, Holmes discovers that the stone was kidnapped by Earl Sylvius with the help of his assistant Sam Merton. The great detective traced the path of the kidnapper, found the kebmen who brought him, and the jeweler, who refused to cut the stone and told everything to Holmes. To return the jewel, the great detective orders his wax statue and hides it in his office behind the curtain.

Count Sylvius arrives on Baker Street. When he sees the statue, he takes it for Holmes and tries to strike from behind, but alive Holmes enters the room and offers the count to return the stone in exchange for Holmes closing the case and no one will know the truth. Count refuses. Holmes invites Sam, invites accomplices to decide whether to return the stone or not, and defiantly leaves for his office to play the violin. Earl and Sam are developing a plan to lead the great detective on the wrong track.Burning with curiosity, Sam asks the owner to let him look at the stone, but when the earl pulls him out, Holmes jumps off the chair where the mannequin stands and takes the jewel. Through a secret door, the great detective entered the office and sat in a chair instead of a statue, and instead of a violin, a gramophone played. The police take the criminals, and Lord Cantlemere arrives on Baker Street. In a conversation with him, Holmes asks who should be considered guilty of the abduction. The lord complacently replies that the culprit will be the one who will find the stone. Holmes takes a stone from the lord's pocket.

The Lord apologizes for doubting Holmes' abilities, and Holmes apologizes for a peculiar joke.