The Unexpected Guest is a short story by Agatha Christie which was first published in issue 1614 of The Sketch on 2 January 1924. It was the first of a series of connected stories to be published in the magazine under the series title "The Man who was Number Four: Further Adventures of M. Poirot". In January 1927, the stories in the series were woven together with minor changes and some additional connecting paragraphs and then published in novel form as The Big Four. Later the same year, in March 1927, the story was published in The Blue Book Magazine. The text in this latter case was the same (with minor abridgements) as in the novel and so this can be considered a serialization of the novel rather than a republication of the original short story carried in The Sketch.
The short story formed the basis for chapters 1 and 2 of the The Big Four ("The Unexpected Guest" and "The Man from the Asylum").
In the Sketch series, this story is followed by The Adventure of the Dartmoor Bungalow.
Back from Argentina, Hastings pays a surprise visit to Poirot and finds, by an unfortunate coincidence, that Poirot is about to leave for South America on a case. Poirot must go: he has promised his client. "Nothing but a matter of life and death could detain me now," Poirot says. And that is just what happens.
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Captain Hastings visits Poirot and finds that Poirot is leaving for South America. He has been offered a huge amount of money by the American "soap king" millionaire Abe Ryland to investigate some irregularities with one of his companies in Rio de Janeiro. Poirot also tells Hastings he has started a investigation of his own on "The Big Four". He thinks it is some organisation of international criminals.
Hastings asks Poirot to delay his departure and return with him to Argentina later but Poirot says he has promised his client and "nothing but a matter of life and death could detain me now." There is a sound in Poirot's bedroom, and an emaciated man caked in mud stumbles out, He keeps repeating "M. Hercule Poirot, 14 Farraway Street" in a strange mechanical voice and then falls silent and unresponsive. They summon a doctor, Dr Ridgeway. He is puzzled by the inability of the patient to speak. He passes him a piece of paper and he begins to scrawl a dozen large figures of the number "4".
Poirot is curious but he has to go. It would take days or even months for the man to recover. It is a pity, Hastings notes. If he were writing a story he would call it "The Mystery of the Big Four". At this, the man suddenly begins speaking telegraphically, as though quoting from a report. He says number 1 is a Chinese political mastermind named Li Chang Yen. He is the brains of the Big Four. Number 2 is usually not named but represented by a '$' or two stripes and a star so he is probably American and he represents wealth. Number 3 is a Frenchwoman and Number 4 is only known as "the destroyer".
They leave the man in the care of Poirot's landlady and then head for the station. Hastings would come back to look after him later. On the train to Southampton, Poirot realises that perhaps the Rio summons is meant to get him out of the way. He and Hastings jump from the train when it stops at a signal and make their way back to London.
They return to the flat to find the man dead. The doctor is summoned and says that the man died of asphyxiation but can't explain how. A man from Hanwell asylum visits them and tells them that the man had escaped from his asylum. He had been there for the last two years. He was harmless enough but had a persecution mania about Chinese secret societies that had locked him up. After the man from the asylum leaves, Poirot reports the event to the police.
Japp arrives and recognizes the man as Mayerling, a secret service agent who went missing five years ago in Russia. Poirot finds both bedroom windows open and also those in the living room. On closer examination, Poirot discovers that Mayerling had been gagged and force to inhale Prussic acid. The windows had been opened to remove the characteristic bitter almond smell. The hands of the lounge clock were stopped at 4 o'clock. Hanwell tells them there has been no escape from their asylum Poirot realizes that the murderer was the man from the asylum and that he was probably "the Destroyer", number 4 of the Big Four. Poirot tells Hastings it will be a duel to the death. They had won the first trick but have failed to get him out of the way and now he is on the case.
- "Poirot tells Hastings that the sum offered to him to take up Ryland's case was "so stupendous" that "for the first and last time in my life, I was tempted by mere money."
- Poirot mentions Giraud. He says that Giraud's methods, resembling that of a human bloodhound, are not for him. He prefers "order and method".
Film, TV, or theatrical versions
Agatha Christie's Poirot
- 1924 The Sketch, Issue 1614 (London), 2 January 1924
- 1927 The Big Four, William Collins and Sons (London), 27 January 1927, Hardcover, 282 pp
- 1927 The Big Four, Dodd Mead and Company (New York), 1927, Hardcover, 276 pp
- 1927 The Blue Book Magazine, Vol. 44 No. 5 (Chicago), March 1927