cavity; and 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 said 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’
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, Tommy and Tuppence tweak this Rule in ‘The Unbreakable Alibi’.
The cipher/code-letter
‘The Four Suspects’, in The Thirteen Problems, features a very clever version of the code-letter and in the last book she wrote, Postern of Fate, Tommy and Tuppence find a hidden message that launches their final case.
The comparison of cigarette butts
‘Murder in the Mews’ features not just this idea but also the clue of the cigarette smoke, or, more accurately, the absence of cigarette smoke.
Knox 2. All supernatural agencies are ruled out as a matter of course.
Van Dine 8. The problem of the crime must be solved by strictly naturalistic means.
These two Rules are, in effect, the same and are more strictly adhered to, but Christie experiments on various occasions, especially in her short story output. The virtually unknown radio play Personal Call has a supernatural twist at the last minute just when the listener thinks that everything has been satisfactorily, and rationally, explained. Dumb Witness features the Tripp sisters, quasi-spiritualists, but apart from her collection The Hound of Death, which has a supernatural rather than a detective theme, most of Chritie’s stories are firmly rooted in the natural, albeit sometimes evil, real world. The Pale Horse makes much of black magic and murder-by-suggestion but, like ‘The Voice in the Dark’
Van Dine 3. There must be no love interest.
Although Van Dine managed this in his own books (thereby reducing them to semi-animated Cluedo), this Rule has been ignored by most successful practitioners. It is in the highest degree unlikely that, in the course of a 250-page novel, the ‘love interest’ can be completely excised while retaining some semblance of verisimilitude. Admittedly, Van Dine may have been thinking of some of the excesses of the Romantic suspense school, when matters of the heart take precedence over matters of the intellect; or when the reader can safely spot the culprit by pairing off the suspects until only one remains. Christie, as usual, turned this rule to her advantage. In some novels we confidently expect certain characters to walk up the aisle, instead of which one or more walk to the scaffold. In Death in the Clouds, Jane Grey gets as big a shock as the reader when the charming Norman Gale is unmasked as a cold-blooded murderer, in Taken at the Flood, Lynn is left pining after the ruthless David Hunter, and in They Came to Baghdad, Victoria is left to seek a replacement for the shy Edward. In some Christie novels the ‘love interest’ or, more accurately, the emotional element and personal interplay between the characters, is not just present but of a much higher standard than usual. In Five Little Pigs, The Hollow and Nemesis it is the emotional entanglements that set the plot in motion and provide the motivation; in each case it is thwarted love that motivates the killer.
Van Dine 16. A detective novel should contain no long descriptive passages, no literary dallying with side-issues, no subtly worked-out character analyses, and no ‘atmospheric’ preoccupations.
This Rule merely mirrors the time in which it was written: and it would be no bad thing to reintroduce it to some present-day practitioners. That said, character analysis and atmosphere can play an important part in a solution. In The Moving Finger, it is only when Miss Marple looks beyond the ‘atmosphere’ of fear in Lymstock that the solutions to both the poison-pen letters and the identity of the murderer become clear. In Cards on the Table the only physical clues are the bridge scorecards and Poirot has to depend largely on the character of the bridge-players, as shown by these scorecards, to arrive at the truth. In Five Little Pigs, an investigation into the murder committed sixteen years earlier has to rely almost solely on the evidence and accounts of the suspects, a procedure largely dependent on character analysis. In The Hollow, it is from his study of the characters staying for the weekend at The Hollow that Poirot uncovers the truth of the crime.
RULE OF THREE: SUMMARY
The Knox Decalogue is by far the more reasonable of the two sets of Rules. Written somewhat tongue-in-cheek – ‘Not more than one secret room or passage is allowable’ – it is less repetitive and restrictive and shows less personal prejudice than does its American counterpart. A strict adherence to Van Dine’s Rules would have resulted in an arid, uninspired and ultimately predictable genre. It would have meant forgoing (much of) the daring brilliance of Christie, the inventive logic of Ellery Queen, the audacious ingenuity of John Dickson Carr or the formidable intelligence of Dorothy L. Sayers. In later years it would have precluded the witty cunning of Edmund Crispin, the erudite originality of Michael Innes or the boundary-pushing output of Julian Symons. Van Dine’s list is repetitive and, in many instances, a reflection of his personal bias: no long descriptive passages, no literary dallying with side-issues, no subtly worked-out character analyses, no ‘atmospheric’ preoccupations. It is somewhat ironic that while the compilers of both lists are largely forgotten nowadays, the writer who managed to break most of their carefully considered Rules remains the best-selling and most popular writer in history.
And so, from The Mysterious Affair at Styles in 1920 until Sleeping Murder in 1976, Agatha – Rule-Keeper and Rule-Breaker – produced at least one book a year and for nearly twenty of those years she produced two titles. The slogan ‘A Christie for Christmas’ was a fixture in Collins’s publishing list and in 1935 it became clear that the name of Agatha Christie was to be a perennial best seller. That year, Three Act Tragedy sold 10,000 hardback copies and this figure trebled over the next decade. By the time of her fiftieth title, A Murder is Announced, she matched it with sales of 50,000; and never looked back. And all of this without the media circus that is now part and parcel of the book trade – no radio or TV interviews, no signing sessions, no question-and-answer
