Van Dine 17. A professional criminal must never be shouldered with the guilt in a detective novel.
This Rule was adhered to and, apart from brief forays into organised crime in The Big Four, The Secret of Chimneys and At Bertram’s Hotel, no use is made of a professional criminal in Christie’s solutions.
Van Dine 12. There must be but one culprit no matter how many murders are committed.
Murderous alliances are a feature of Christie’s fiction beginning with The Mysterious Affair at Styles and continuing with The Murder at the Vicarage, Death on the Nile, One, Two, Buckle my Shoe, Evil under the Sun, The Body in the Library, Sparkling Cyanide and Endless Night, all of which feature murderous couples. Cat among the Pigeons and, to a lesser degree, Taken at the Flood, feature more than one killer working independently of each other; The Hollow features an unusual and morally questionable, collusion; and, of course, Murder on the Orient Express features the ultimate conspiracy.
The murder method
Christie never resorted to elaborate mechanical or scientific means to explain her ingenuity, and much of her popularity and accessibility lies in her adherence to this simplicity. Many of her last-chapter surprises can be explained in a few sentences. Once you have grasped the essential fact that the corpse identified as A is, in fact, Corpse B and vice versa everything else falls into place; when you realise that all twelve suspects conspired to murder one victim all confusion disappears; when it dawns that the name Evelyn can mean a male or a female little further explanation is necessary.
Van Dine 14. The method of murder, and the means of detecting it, must be rational and scientific.
Knox 4. No hitherto undiscovered poisons may be used, nor any appliance which will need long scientific explanation at the end.
While Christie uses poisons as a means of killing characters more than any of her contemporaries, she uses only those that are scientifically known. But, that said, thanks to her training as a dispenser, she had more knowledge of the subject than many of her fellow writers and was familiar with unusual poisons and the more unusual properties of the common ones. Her first novel, The Mysterious Affair at Styles, depends for its surprise solution on knowledge of the properties of strychnine, but this is not unreasonable as the reader is fully aware of the poison used. In fact, there is a graphic description of the death of Mrs Inglethorpe and a discussion of the effects of, and the chemical formula for, strychnine. Taxine in A Pocket Full of Rye, ricin in ‘The House of Lurking Death’ from Partners in Crime, thallium in The Pale Horse and physostigmine in Crooked House are just some of the unusual poisons featuring in Christie. Fictitious drugs such as Serenite in A Caribbean Mystery, Calmo in The Mirror Crack’d from Side to Side and Benvo in Passenger to Frankfurt also feature, but as the plot does not turn on their usage, they merely bend rather than break Knox’s Rule.
To be avoided
Some of these items are mere personal prejudice; there is no good reason why cigarettes or twins, for instance, cannot be a clue, or even a main plot device, provided that the reader has been properly prepared for them. With all of these the important point is the originality of the approach in utilising them – and this Christie had in full measure and overflowing.
Van Dine 13. Secret societies have no place in a detective story.
Many readers, including probably the author herself, would wish that The Big Four had never found its way between hard covers. Cobbled together at the lowest point in her life (after the death of her mother, the request for a divorce from her husband and her subsequent disappearance) with the help of her brother-in-law, Campbell Christie, this collection of short stories that had earlier appeared in various magazines was turned into a novel by judicious editing. The ‘secret society’ bent on world domination that it features was, mercifully, a one-off aberration on Christie’s part. The Seven Dials Mystery features an equally preposterous secret society, albeit one with a Christie twist. Throughout the novel we are told of the existence of this society and the reader assumes the worst. At the eventual and literal unmasking we discover that it is actually working for the eradication, rather than the promotion, of crime, and its membership includes Superintendent Battle. The Pale Horse, one of the best books of the 1960s, features a mysterious organisation, Murder Inc., that seems to specialise in remote killing, but a rational and horribly plausible method of murder is revealed in the closing chapters.
Knox 5. No Chinamen must figure in the story.
This comment is not as racist as it may first appear. At the time of its writing Orientals in fiction were perceived as the personification of everything undesirable and came under the general heading of ‘The Yellow Peril’. A more lengthy discussion of the subject can be found in Colin Watson’s Snobbery with Violence (1971), an investigation of the social attitudes reflected in British crime fiction of the twentieth century, but suffice it to say that the white-slave trade, torture and other ‘unspeakable acts’ were the accepted fictional norms at the time for any character of Oriental extraction. This Rule was included to raise the literary horizon above that of the average opium den. Apart from The Big Four, and the more politically correct Poirot case ‘The Lost Mine’ in 1923, no ‘Chinamen’ play a part in any of Christie’s detective novels. Unfortunately, she succumbs to stereotype in The Big Four where, as well as some cringe-inducing scenes with Oriental characters and ‘speech’, the chief villain, ‘the greatest criminal brain of all time’, is Chinese. But these stories had appeared some years earlier, pre-dating Knox.
Knox 3. Not more than one secret room or passage is allowable.
This Rule is taken to mean that no solution may turn on the existence of a secret passage. It was designed to eliminate the possibility of an exasperated reader hurling his detective novel across the room as the detective explains how the killer gained access to his closely guarded victim through such a passage, the existence of which was unknown up to that point. Christie is not above introducing the odd secret passage almost as a challenge to the cliché, but their very introduction long before the solution is in keeping with the tenet of this Rule. The Secret of Chimneys, Three Act Tragedy and ‘The Adventure of Johnny Waverley’ all feature, but openly and not covertly, a secret room or passage. The play Spider’s Web features a sliding panel with a concealed cavity; but its use pokes gentle fun at this convention.
Knox 10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
This Rule was formalised in an effort to avoid the disclosure that Suspect A, who had a cast-iron alibi for the night of the crime, was the guilty party because his alibi was provided by a hitherto unheard-of twin brother. Tongue firmly planted in literary cheek, Christie cocks a snook at this convention in ‘The Unbreakable Alibi’ in Partners in Crime. This is her take on the alibi-breaking stories of her contemporary Freeman Wills Crofts. And look at the ingenious double-bluff of Lord Edgware Dies. The Big Four also has an episode featuring a twin – one Achille Poirot …
Van Dine 20. A list of devices, which no self-respecting detective story writer should avail himself of …
The bogus séance to force a confession
At the end of Peril at End House Poirot arranges something very like a séance in End House, but it is really a variation on his usual ‘all-the-suspects-in-the-drawing-room’ ploy – although he does manage to elicit a confession. At the other end of a story is the séance in The Sittaford Mystery, where such an event is cleverly stage-managed in order to set a plot in motion.
The unmasking of a twin or look-alike
In Partners in Crime, Christie has Tommy and Tuppence tweak this Rule in ‘The Unbreakable