"The Adventure of the Mazarin Stone" is a Sherlock Holmes short story by the British author Sir Arthur Conan Doyle. It was first published in 1921, appearing in the October 1921 issue of The Strand magazine in the United Kingdom and the November 1921 issue of Hearst's International Magazine in the United States. It was published again in 1927 as part of the anthology The Casebook of Sherlock Holmes. Doyle adapted the story from his own 1921 stage play The Crown Diamond: An Evening with Sherlock Holmes, which is itself partially inspired by Doyle's own 1903 short story "The Adventure of the Empty House". Unusually for a Sherlock Holmes story, "The Adventure of the Mazarin Stone" is not told from the point of view of Dr. John Watson but is instead narrated in the third person.
In the story, the Mazarin Stone, a yellow diamond which is part of the British Crown jewels, has been stolen. The brilliant consulting detective Sherlock Holmes has been hired by the British government to find and return the diamond. Holmes finds out that the gem has been stolen by Count Negretto Sylvius with the assistance of a boxer called Sam Merton. However, Holmes does not know where the diamond itself is being kept. The detective manages to fool the two men into thinking that they can talk freely about the stolen gem and manages to take it from them.
The stage origins of "The Adventure of the Mazarin Stone" are obvious. Most of the story is made up of dialog. All of the action takes place within a very short period of time and in only one room, the living room of Sherlock Holmes' Baker Street apartment.
"The Adventure of the Mazarin Stone' has been adapted for film and television.
Dr. John Watson comes to visit the home of his friend and former roommate Sherlock Holmes. Although it is only seven o'clock on a summer evening, Holmes' young servant Billy says that the detective is asleep. Watson realizes that Holmes must be tired because he is working on a difficult case. Billy confirms this. He reminds Watson that the Mazarin Stone, one of the Crown jewels, a yellow diamond worth a hundred thousand pounds, was recently stolen. Holmes has been asked by the government to find and return the stone. As a result, the Prime Minister and Home Secretary have been frequent visitors to Holmes' Baker Street apartment, as has a man called Lord Cantlemere. Lord Cantlemere thinks that the government made a mistake by hiring Holmes and seems to want him to fail to find the diamond.
Watson notices that the window has been covered by a curtain. Billy shows Watson that there is "something funny" behind it. Seated in an armchair behind the curtain is a dummy which looks exactly like Sherlock Holmes. The dummy has its head bent down, making it look as if it is reading a book. Billy says that the dummy is routinely moved a little in order to make it appear more lifelike. Billy says that people are watching Holmes' apartment from the building across the street and that the dummy is intended to fool them. Watson says that Holmes did something similar before. Sherlock Holmes emerges from his bedroom. He tells Billy to get away from the window because it is dangerous.
Holmes tells Watson that a man called Count Negretto Sylvius plans to kill him. Watson asks why Holmes does not have the man arrested. Holmes replies that it is because he does not know where the Mazarin Stone is yet. Although he does not know where the diamond has been hidden, Holmes knows that Count Negretto Sylvius and his accomplice the boxer Sam Merton stole it. He has gathered evidence by following Count Sylvius in disguise. Sherlock Holmes also knows that Count sylvius recently ordered the manufacture of an air gun. Holmes believes that, as he speaks, the air gun is being aimed at his apartment from the building across the street.
Billy returns with the business card of a man who is waiting to see Holmes. It is the card of Count Negretto Sylvius. Holmes asks Watson to look out the window and see if any people are loitering in the street. Watson says that he can see a "rough fellow". Holmes realizes that must be the Count's accomplice Sam Merton. Holmes writes a note, gives it to Watson and tells him to give it to Inspector Youghal at Scotland Yard. Holmes and Watson go into Holmes bedroom, which has a door that leads out of the building.
Count Negretto Sylvius is shown into the empty living room. He notices the dummy of Holmes and mistakes it for the real detective. He creeps up behind the armchair, preparing to strike the dummy with his walking stick. Just as he is about to hit it, the real Holmes comes out of his bedroom and tells the count not to break the dummy. Holmes persuades Count Sylvius to sit down and talk. Count Sylvius angrily accuses Sherlock Holmes of sending spies, an old man an old woman, to follow him. Holmes says that he has not sent anyone else to follow the Count. Both the old man ans the old woman were Holmes in disguise. This revelation makes the Count even more angry.
Sherlock Holmes tells Count Sylvius that he knows that the Count stole the Mazarin Stone. He has the testimony of the cabmen who took Count Sylvius to and from the museum where the diamond was kept. He has a statement from a guard at the museum who saw Count Sylvius standing close to the diamond's display case. The jeweler Ikey Sanders also told Holmes that he refused to cut the Mazarin Stone for the Count. Although Holmes does not know where the Count has hidden the Mazarin Stone, there is enough evidence to have Count Sylvius and Sam Merton arrested. However, Holmes has been tasked with finding the diamond rather than its thief. Count Sylvius and Sam Merton can avoid going to prison for twenty years if they hand the diamond over to Holmes. The detective says that the Count should discuss the matter with Sam Merton.
Billy is asked to bring Sam Merton in from the street. Holmes says that, so that Count Sylvius and Sam can discuss the matter freely, he will go into his bedroom and play his violin. The count and Sam are confident that Holmes cannot hear them over the sound of his noisy violin. Sam, however, thinks that somebody else might be hiding in the room and listening to them. he notices the dummy in the armchair by the window. The Count tells him that it is not a real person. The two men hear a noise but conclude that it came from the street and that they do not need to worry about it.
Sam Merton suggests killing Holmes. The Count says that would not help because Holmes will have already passed on all the evidence that he gathered to the police. He decides that the best thing to do is to make a false confession to Holmes. The Count plans to tell Holmes that the Mazarin Stone, which has been in his pocket all the time, is in Liverpool. He will then arrange for a Dutchman called Van Sedder to take the diamond to Amsterdam to be cut into four pieces. Sam wants to see the diamond. Count Sylvius does not want to hand the diamond over to him but agrees to show it to him. The two men go to the window so that the Count can hold the Mazarin Stone up to the light. When he does so, Holmes snatches the diamond out of Count Sylvius' hand. Holmes has taken the dummy's place in the armchair. He explains that there is a second door from his bedroom which comes out behind a curtain next to the window. The noise which Count Sylvius and Sam Merton heard and ignored was Holmes taking the dummy out of the chair. The violin music that they heard was a gramophone record. Watson returns with the police. Count Sylvius and Sam Merton are arrested.
Lord Cantlemere arrives. Holmes asks him to take off his coat. Lord Cantlemere believes that Holmes has been unable to find out anything about the theft of the Mazarin Stone, a belief which Holmes encourages. Holmes tells Lord Cantlemere that he believes that the thieves stole on someone else's orders. Lord Cantlemre says that the person who ordered the theft should also be arrested. He says that possession of the diamond would be proof of that person's guilt. Holmes says that, in that case, Lord Cantlemere should be arrested. Lord Cantlemere finds that the Mazarin Stone is in his coat pocket, Holmes having placed it there when he took off the coat. Lord Cantlemere realizes that Holmes is only joking and not really accusing him of involvement in the theft. He is happy that the stolen diamond has been recovered.
The story was adapted as the 1923 silent movie The Stone of Mazarin which stars Ellie Norwood as Sherlock Holmes.
The 1946 Hollywood movie Terror by Night, which stars Basil Rathbone as Holmes and Nigel Bruce as Watson, is inspired by "The Adventure of the Mazarin Stone", "The Adventure of the Empty House", "The Disappearance of Lady Frances Carfax" and The Sign of the Four.
"The Mazarin Stone", the fifth episode of the Granada TV series The Memoirs of Sherlock Holmes, is an adaptation of "The Adventure of the Mazarin Stone" and the 1924 story "The Adventure of the Three Garridebs". It first aired in the United Kingdom on the ITV network on April 4, 1994. Sherlock Holmes himself (played by Jeremy Brett) appears only very briefly at the beginning and the end of the episode. He announces at the start of the episode that he is leaving to pursue another case over which he has been obsessing. With Sherlock Holmes away, his brother Mycroft (played by Charles Gray) is tasked by the British government with recovering the stolen gem. Meanwhile, Dr. Watson (played by Edward Hardwicke) is approached by the sisters of his former university lecturer Nathan Garrideb with another mystery. The two cases ultimately prove to be connected.
An adaptation of the story, starring Clive Merrison as Holmes and Michael Williams as Watson, first aired on BBC Radio 4 in the United Kingdom on October 5, 1994. Holmes' housekeeper Mrs. Hudson replaces the young male servant Billy in the radio adaptation.
In the 1974 Sherlock Holmes novel The Seven Per-Cent Solution by the American author Nicholas Meyer, Dr. Watson dismisses "The Adventure of the Mazarin Stone' as "drivel" and claims that it is one of four Sherlock Holmes stories, the other three being "The Adventure of the Lion's Mane", "The Adventure of the Three Gables" and "The Adventure of the Creeping Man", that are complete forgeries.
- The only other one of Sir Arthur Conan Doyle's fifty-six canonical Sherlock Holmes stories to be narrated in the third person is the 1917 story "His Last Bow".
- The character of Billy was not created by Sir Arthur Conan Doyle. He first appeared in the 1899 stage play Sherlock Holmes by William Gillette.
- Watson appears to be referring to the 1903 short story "The Adventure of the Empty House" in which Holmes uses a dummy to fool would-be assassins.
- In the original stage play The Crown Diamond: An Evening with Sherlock Holmes, it is Colonel Sebastian Moran, the antagonist from "The Adventure of the Empty House", who has stolen the diamond and who plans to kill Holmes.
- Sherlock Holmes' brother Mycroft only appears in three of Sir Arthur Conan Doyle's fifty-six canonical Sherlock Holmes short stories, "The Adventure of the Greek Interpreter" (1893), "The Final Problem" (1893) and "The Adventure of the Bruce-Partington Plans" (1908). However, Mycroft Holmes appears in four episodes of the Granada TV Sherlock Holmes series, "The Greek Interpreter" (1985), "The Bruce-Partington Plans" (1988), "The Golden Pince-Nez" (1994) and "The Mazarin Stone" (1994).