There are, unfortunately, a few examples in Christie’s oeuvre of ‘deductions’ not based on any tangible evidence. It must be conceded that they can only be accounted for only by intuition. How, for example, does Miss Marple alight on Dr Quimper in 4.50 from Paddington?
The crime
The crime itself did not feature strongly in the Rules, although Christie enjoyed the challenge of Van Dine 18 below.
Van Dine 7. There simply must be a corpse in a detective novel.
Although the first detective novel, Wilkie Collins’ The Moonstone (1868), concerns a robbery rather than a murder, a mysterious death is the sine qua non of most detective novels. Although she broke this Rule often in her short story output, Christie almost never short-changed her readers in novel form, generously providing a multitude of corpses in And Then There Were None, Death Comes as the End and Endless Night – but there is no corpse discovered in Five Little Pigs.
Van Dine 18. A crime in a detective story must never turn out to be an accident or a suicide.
The rejection of this Rule could mean a huge disappointment for a reader who discovers, after 250 pages, that the death under investigation is not a crime at all. See how cleverly Agatha Christie overcomes this in Taken at the Flood, when none of the deaths is what it first seems. The seeming murder of ‘Enoch Arden’ is an accident, the death of Major Porter is suicide and the seeming suicide of Rosaleen Cloade is murder. In one brilliant plot she effortlessly breaks both aspects of Van Dine’s Rule. In the Poirot cases ‘The Market Basing Mystery’ and ‘Murder in the Mews’ – both essentially the same story, the latter being a more elaborate version, of the former – we have not murder disguised to look like suicide but suicide disguised to look like murder. But there is another twist; the real murder plan is to get someone else hanged (and therefore murdered) for a crime they did not commit.
Van Dine 19. The motives for all the crimes in detective stories should be personal.
This Rule essentially outlawed murder committed for ideological reasons, with Van Dine suggesting that such murders should be confined to secret-service stories. Appropriately, this type of plot does feature in some of Christie’s international thriller novels – They Came to Baghdad, Destination Unknown, Passenger to Frankfurt – as well as some of the early titles – The Secret Adversary, The Secret of Chimneys – but it is not a feature of her detective fiction. But into which category does the motive for the first murder in Three Act Tragedy fall?
The detective
The figure of the detective occupied both writers: Van Dine 4 and Knox 7 are identical, although Van Dine added further embellishments in Rules 6 and 9. Some of Christie’s greatest triumphs involve these Rules; she has joyously shattered all of them.
Van Dine 4. The detective himself, or one of the official investigators, should never turn out to be the criminal.
Knox 7. The detective must not himself commit the crime.
From the very beginning of the detective novel the unmasking of the official investigator was considered a valid ploy. The Mystery of the Yellow Room (1907) by Gaston Leroux, creator of The Phantom of the Opera, is credited in An Autobiography as being one of the two detective novels that Christie had enjoyed before embarking on The Mysterious Affair at Styles. It features one of the earliest examples of the criminal investigator, and in The Clocks, Poirot is unstinting in his praise for this groundbreaking novel. Some of Christie’s most deftly plotted books featured this ploy. Hercule Poirot’s Christmas was chosen by Robert Barnard, in his Agatha Christie: A Talent to Deceive (1980), as one of the three best novels of Dame Agatha’s career, and indeed it is a classic Golden Age detective story: a snowbound country mansion, a murder, a group of suspects, a killer and a solution, breathtaking in its daring. An early foreshadowing of this ploy can also be found in ‘The Man in the Mist’
The Mousetrap, in both its stage and novella versions, and its earlier incarnation as the radio play Three Blind Mice, all unmask the investigator as the villain. Sergeant Trotter arrives like a deus ex machina in Monkswell Manor and is accepted unquestioningly both by its snowbound inhabitants and by the audience, although he is an imposter and not an actual policeman. In the late 1940s and early 1950s the policeman, like the village doctor, was perceived as uncorrupted and incorruptible, although modern audiences are more likely to spot this type of villain than their more innocent counterparts of an earlier age.
In Curtain: Poirot’s Last Case, Agatha Christie played the last and greatest trick of all on her readers; and they admired her all the more for it. The ultimate sleight of hand from the supreme prestidigitator in the crime-writing pantheon, who but Agatha Christie would have thought of, and then carried out, this almost sacrilegious trick? After a half century of partnership, she unmasks Poirot as the killer. Certainly the book is contrived (which detective story is not?), but only the most churlish of readers would complain after such a dazzling culmination of two careers.
Van Dine 6. The detective novel must have a detective in it.
This is a perfectly reasonable Rule. But Agatha Christie made a career out of breaking the Rules, reasonable or otherwise, and she managed to demolish this one also. The most famous and best-selling crime novel of all time, And Then There Were None, has no detective, although, arguably, every character in the book is Victim, Murderer and Detective …; Death Comes as the End is also an example of a detectiveless detective novel. Its setting of Ancient Egypt 4,000 years ago does, however pre-date the Rules by some time.
Van Dine 9. There must be but one detective.
In the sense that Hercule Poirot and Miss Marple never meet between the covers of any of her books Agatha Christie abided by this Rule, but in many novels they work in close collaboration with the official investigators. And other titles feature an unofficial coming-together of, effectively, suspects in order to solve the crime. Three Act Tragedy, Death in the Clouds and The ABC Murders find Poirot working alongside some of those under suspicion in order to arrive at the truth. And in all three cases one of his group of collaborators is unmasked in the last chapter. Coincidentally or otherwise, these novels were all published in the same 12-month period between January 1935 and January 1936.
The murderer
The other important figure, the murderer, also exercised both rule-makers. But Christie had broken most of these Rules before either Knox or Van Dine even compiled them.
Knox 1. The criminal must be someone mentioned in the early part of the story, but must not be anyone whose thoughts the reader has been allowed to follow.
While adhering to the former part of this injunction, the circumvention of the latter became almost a motif throughout Agatha Christie’s writing life. As early as 1924 with The Man in the Brown Suit she neatly and unobtrusively breaks this rule, via Sir Eustace Pedler’s diary. The most famous, or infamous, example is, of course, The Murder of Roger Ackroyd, her first for the publisher Collins. The book immediately ensured her fame and success and it is safe to assert that, even if she had never written another word, her name would still be remembered today in recognition of this stunning conjuring trick. Forty years later she replayed