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. Every reader must admit that the bet was won."[4]
The New York Times Book Review (26 December 1920),[5] was also impressed:
Though this may be the first published book of Miss Agatha Christie, she betrays the cunning of an old hand... You must wait for the last-but-one chapter in the book for the last link in the chain of evidence that enabled Mr Poirot to unravel the whole complicated plot and lay the guilt where it really belonged. 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. The story, moreover, has no lack of movement, and the several characters are well drawn."[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. To wit,
It will rejoice the heart of all who truly relish detective stories, from Mr McKenna downwards. I have heard that this is Miss Christie's first book, and that she wrote it in response to a challenge. If so, the feat was amazing, for the book is put together so deftly that I can remember no recent book of the kind, which approaches it in merit. It is well written, well proportioned, and full of surprises. When does the reader first suspect the murderer? 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. But I was not in the least degree prepared to find that his accomplice was the woman who pretended to be a friend. 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. I hope I have not revealed too much of the plot. Lovers of good detective stories will, without exception, rejoice in this book.[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. Poirot has a few questions for her fortune-hunting new spouse, her aimless stepsons, her private doctor, and her hired companion. The answers are positively poisonous. Who's responsible, and why, can only be revealed by the master detective himself." (Book jacket, Berkley Book edition April 1984)
In his book, A Talent to Deceive – An Appreciation of Agatha Christie, Robert Barnard wrote:
Christie's debut novel, from which she made £25 and John Lane made goodness knows how much. The Big House in wartime, with privations, war work and rumours of spies. Her hand was over-liberal with clues and red herrings, but it was a highly cunning hand, even at this stage[8]: 200
In general The Mysterious Affair at Styles is a considerable achievement for a first-off author. The country-house-party murder is a stereotype in the detective-story genre, which Christie makes no great use of. Not her sort of occasion, at least later in life, and perhaps not really her class. The family party is much more in her line, and this is what we have here. This is one of the few Christies anchored in time and space: we are in Essex, during the First World War. 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 marriage of the matriarch with a mysterious nobody is the central out-of-joint event in an intricate web of subtle changes. 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. It is, too, a very clever story, with clues and red herrings falling thick and fast. 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. These were problems which Conan Doyle never satisfactorily overcame, but which Christie would.".[8]: 22–23
In the "Binge!" 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".[16]
