The Adventure of the Mazarin Stone is one of 12 Sherlock Holmes short stories by Arthur Conan Doyle in The Case-Book of Sherlock Holmes. It was first published in the Strand Magazine in October 1921.

Watson arrives in 221B Baker Street where the page boy Billy shows him a wax effigy of Holmes placed near a curtained window in the sitting room. The effigy produces a shadow on the curtain that, when viewed from outside, is the unmistakable profile of Sherlock Holmes. Using this visual trick, Holmes aims to give a perfect target to a would-be murderer with a rifle. Holmes names his murderer as Count Negretto Sylvius, the diamond thief he has been following in disguise. He gives the criminal's address to Watson, then sends the doctor out the back for the police. As the Count arrives, Holmes has Billy invite him inside, then takes him by surprise when he attempts an assault on the effigy. Holmes then offers the Count and his helper, boxer Sam Merton, freedom if they give up the jewel, or jail if not.He invites them to discuss the deal while he plays violin in the next room. When the Count decides to double-cross Holmes and takes the stone from his secret pocket to show Sam in window light, the detective springs from the chair in place of his replica and grabs the £100K jewel. His bedroom has a gramophone and secret passage to behind the curtain.After the police take away the villains, Lord Cantlemere sweeps in. Unlike the Prime Minister and Home Secretary, he did not want Holmes. When tricked into insisting on arrest for whoever is found possessing the diamond, he finds the jewel in his pocket – where Holmes has placed it – and apologizes. Finally, Holmes can eat.

Famous works of the author Arthur Conan Doyle: A Study in Scarlet, The Sign of the Four, The Adventures of Sherlock Holmes, The Memoirs of Sherlock Holmes, The Hound of the Baskervilles, The Return of Sherlock Holmes, The Valley of Fear, His Last Bow, The Case-Book of Sherlock Holmes, Stories of Sherlock Holmes, The Lost World.