[3] Poirot, a Belgian refugee of the Great War, is settling in England near the home of Emily Inglethorp, who helped him to his new life.

"[8]: 22–23 The story features many of the elements that have become icons of the Golden Age of Detective Fiction, largely due to Christie's influence.

After keeping the submission for several months, The Bodley Head's founder, John Lane, offered to accept it, provided that Christie make slight changes to the ending.

[2] During the First World War, Arthur Hastings is on sick leave from the Western Front and is invited to stay at the manor house of Styles Court in Essex by his old friend John Cavendish.

On the morning of 18 July, the Styles household wakes to the discovery that Emily Inglethorp, the elderly and wealthy owner, has died.

Hastings ventures out to the nearby village of Styles St Mary to enlist help from his friend Hercule Poirot.

Emily's household includes her husband, Alfred Inglethorp — a younger man she recently married; her stepsons (from her first husband's previous marriage) John and Lawrence Cavendish; John's wife Mary Cavendish; Cynthia Murdoch, the daughter of a deceased friend of the family; and Evelyn Howard, Emily's lady's companion.

This caused the low level of strychnine in the medicine to precipitate to the bottom of the bottle, making the final dose lethal.

The Times Literary Supplement (3 February 1921) gave the book an enthusiastic, if short, review, which stated: "The only fault this story has is that it is almost too ingenious."

It went on to describe the basic set-up of the plot and concluded: "It is said to be the author's first book, and the result of a bet about the possibility of writing a detective story in which the reader would not be able to spot the criminal.

And you may safely make a wager with yourself that until you have heard M. Poirot's final word on the mysterious affair at Styles, you will be kept guessing at its solution and will most certainly never lay down this most entertaining book.The novel's review in The Sunday Times of 20 February 1921, quoted the publisher's promotional blurb concerning Christie writing the book as the result of a bet that she would not be able to do so without the reader being able to guess the murderer, then said, "Personally we did not find the "spotting" so very difficult, but we are free to admit that the story is, especially for a first adventure in fiction, very well contrived, and that the solution of the mystery is the result of logical deduction.

"[6] The contributor who wrote his column under the pseudonym of "A Man of Kent" in the 10 February 1921 issue of the Christian newspaper The British Weekly praised the novel but was overly generous in giving away the identity of the murderers.

For my part, I made up my mind from the beginning that the middle-aged husband of the old lady was in every way qualified to murder her, and I refused to surrender this conviction when suspicion of him is scattered for a moment.

I ought to say, however, that an expert in detective stories with whom I discussed it, said he was convinced from the beginning that the true culprit was the woman whom the victim in her lifetime believed to be her staunchest friend.

[7]The Bodley Head quoted excerpts from this review in future books by Christie but, understandably, did not use those passages which gave away the identity of the culprits.

"Introducing Hercule Poirot, the brilliant – and eccentric – detective who, at a friend's request, steps out of retirement – and into the shadows of a classic mystery on the outskirts of Essex.

The victim is the wealthy mistress of Styles Court, found in her locked bedroom with the name of her late husband on her dying lips.

The family is kept together under one roof by the exigencies of war and of a matriarch demanding rather than tyrannical – not one of her later splendid monsters, but a sympathetic and lightly shaded characterisation.

If the lifestyle of the family still seems to us lavish, even wasteful, nevertheless we have the half sense that we are witnessing the beginning of the end of the Edwardian summer, that the era of country-house living has entered its final phase.

Christie takes advantage of this end-of-an-era feeling in several ways: while she uses the full range of servants and their testimony, a sense of decline, of break-up is evident; feudal attitudes exist, but they crack easily.

The family is lightly but effectively characterised, and on the outskirts of the story are the villagers, the small businessmen, and the surrounding farmers – the nucleus of Mayhem Parva.

We are entering the age when plans of the house were an indispensable aid to the aspirant solver of detective stories, and when cleverness was more important than suspense.

But here we come to a problem that Agatha Christie has not yet solved, for cleverness over the long length easily becomes exhausting, and too many clues tend to cancel each other out, as far as reader interest is concerned.

article of Entertainment Weekly Issue #1343-44 (26 December 2014–3 January 2015), the writers picked The Mysterious Affair at Styles as an "EW favorite" on the list of the "Nine Great Christie Novels".

The cast included David Suchet as Hercule Poirot, Hugh Fraser as Lieutenant Arthur Hastings and Philip Jackson as Inspector James Japp.

The cast included Arnolds Liniņš [lv] as Puaro (Poirot's name in Latvian) and Romāns Birmanis as Hastingss (Hastings).

One difference from the novel is that the inquest hearing is omitted, and instead there are more scenes from Džaps and Samerhejs (Japp and Summerhaye) searching for clues at Styles Court.

This version has many differences from the novel, but the core story is the same: a wealthy old woman is murdered by her husband together with her top business partner, who appear to hate each other but are secretly lovers.

[20] On 14 February 2012, Great Lakes Theater in Cleveland, Ohio debuted a 65-minute stage adaptation as part of their educational programming.

This novel has had the unique distinction for a first book of being accepted by the Times as a serial for its weekly edition.The Mysterious Affair at Styles is in the public domain in the US.