The Mysterious Mr Quin is a short story collection by British writer Agatha Christie, first published in the UK by William Collins & Sons on 14 April 1930[1] and in the US by Dodd, Mead and Company later in the same year.

Satterthwaite is a small, observant man who is able to wrap up each mystery through the careful prodding and apposite questions of Quin, who serves as a catalyst each time the men meet.

All agree that Capel's manner that night was like a man who had won a large gamble and was defying the odds, yet ten minutes later he shot himself.

Quin asks them to place the exact date, possibly by reference to some event in the news, and the men remember it was the time of the Appleton murder trial.

His wife, who had smashed a decanter of port from which her husband had drunk – perhaps to destroy the evidence – had been put on trial and found not guilty, but had then left the country because of the scandal.

Quin takes the men through the sequence of events: Capel saw the paragraph in the newspaper reporting that the exhumation order had been given; then he saw a policeman approaching his house.

His audience is stunned at the accusation that Capel was a murderer, objecting that he was not at the Appleton home on the day of the death; but Quin points out that strychnine is not soluble and would collect at the bottom of the decanter if placed there a week before.

The next evening, Satterthwaite and Porter retrace their steps in the dusk to the grassy knoll and conclude that the glass is not yet replaced, as the cavalier's image is still there.

Quin describes the crime – Richard Scott pulled the movable panel back, knowing the house well, and then saw his wife and her lover in the garden.

Just over a year earlier, the large local house, Ashley Grange, was bought by Miss Eleanor Le Couteau, a rich young French Canadian, with a taste for collecting and for the hunt.

Quin points out that Miss Le Couteau's past is as little known as that of Harwell, and she, her husband, and Mrs Mathias could easily be the Clondinis in disguise, staging this elaborate laundering of the proceeds of their crime.

On the morning of Friday the 13th Lady Barnaby sent him a letter, begging him to come to her house at Deering Hill that evening at six o'clock, when her husband would be out at a bridge game.

She speaks of seeing the shape of a giant hand in the sky caused by the smoke of a passing train at the very time she heard the shot.

She does tell Satterthwaite that Henry Thompson suggested the post in Canada to her, with its high wages, and she had to leave quickly to take it, as well as refrain from letters to her friends at Deering Hill.

Satterthwaite realises that Sir George put the clocks back by ten minutes to give himself an alibi; he had intercepted his wife's note that morning.

The following night at the casino the Countess wears a simple white gown and no jewelry, and a younger woman is rumoured to be the lover of the king of Bosnia.

Quin tells him that the man who drowned in the sea twenty years ago truly loved his wife – almost to the point of madness – and the desire to make amends for past transgressions can sometimes be so strong that a messenger can be found.

Gillian is nervous of the effect the news will have on Philip Eastney, and Charlie confides that, in the past, men have lost their heads over his fiancée and done stupid things as a result.

Satterthwaite is uneasy as he leaves Gillian, feeling that the appearance of Quin at Covent Garden must mean that there is unusual business afoot, but he cannot place exactly what is going to happen.

Quin is not there, but Eastney is, and the two men talk – the younger man regaling Satterthwaite with tales of working in the testing and manufacture of poison gas during the war.

A stray cat goes through the door to the flat and is found dead – killed by the gasses freed from the glass ball when it shattered as a result of the tenor singing.

The house has a ghostly history, with the spectre of Charles I walking headless on the terrace and a weeping lady with a silver ewer seen whenever there is a tragedy in the family.

Monkton thinks that explains all, but Satterthwaite wants to know why Bristow's picture portrays the dead figure in the Terrace Room and not in the Oak Parlour.

Any bloodstain on the floor of the Terrace Room would have been covered by a red Bokhara rug which was placed there on that night only, and the body then moved into the Oak Parlour.

At the appointed time they drive up into the mountains and eventually stop where the road finishes at an isolated coastal village of the name of Coti-Chiavari, which Naomi Smith terms "the World's End".

The Times Literary Supplement review of 29 May 1930 failed to comment on the merits of the book, confining itself to summarising the relationship between Quin and Satterthwaite and concluding that the latter is helped "to solve old mysteries, sometimes to restore happiness to the unfortunate, and sometimes to see, if not avert, impending tragedy".

"[8] In The Dead Harlequin, the character of Aspasia Glen is an early attempt by Christie to portray the acclaimed American monologist Ruth Draper (1884–1956).

A second series of abridged readings ("The World's End", "The Face of Helen", "The Sign in the Sky") was broadcast 15–17 September 2010 on BBC Radio 4 and again performed by Martin Jarvis.

The blurb of the first edition (which is carried on both the back of the dustjacket and opposite the title page) reads: Mr Satterthwaite is a dried-up elderly little man who has never known romance or adventure himself.

Prompted by his mystic influence, Mr Satterthwaite plays a real part in life at last, and unravels mysteries that seem incapable of solution.