The wrongly suspected person
This is the basis of some of Christie’s finest titles, among them the novels Five Little Pigs, Sad Cypress, Mrs McGinty’s Dead and Ordeal by Innocence, and the short story ‘Witness for the Prosecution’. The wrongly suspected may be still on trial as in Sad Cypress or already convicted as in Mrs McGinty’s Dead. In more extreme cases – Five Little Pigs, Ordeal by Innocence – they have already paid the ultimate price, although in each case ill-health, rather than the hangman, is the cause of death. And being Agatha Christie, she also played a variation on this theme in ‘Witness for the Prosecution’ when the vindicated suspect is shown to be the guilty party after all.
The sealed room
The fascination with this ploy lies in the seeming impossibility of the crime. Not only has the detective – and the reader – to work out ‘Who’ but also ‘How’. The crime may be committed in a room with all the doors and windows locked from the inside, making the murderer’s escape seemingly impossible; or in a room that is under constant observation; or the corpse may be discovered in a garden of unmarked snow or on a beach of unmarked sand. Although this was not a favourite Christie ploy she experimented with it on a few occasions, but in each case – Murder in Mesopotamia, Hercule Poirot’s Christmas, ‘Dead Man’s Mirror’, ‘The Dream’ – the sealed-room element was merely an aspect of the story and not its main focus.
The unexpected solution
Throughout her career this was the perennial province of Agatha Christie and the novels Murder on the Orient Express, Endless Night and And Then There Were None, as well as the short story ‘Witness for the Prosecution’, are the more dramatic examples. But mere unexpectedness is not sufficient; it must be fairly clued and prepared. The unmasking of, for example, the under-housemaid’s wheelchair-bound cousin from Australia, of whom the reader has never heard, may be unexpected but it is hardly fair. The unexpected murderer is dealt with below.
The ‘armchair detective’ and the application of pure reasoning
In 1842, Poe’s story ‘The Mystery of Marie Roget’ was an example both of ‘faction’, the fictionalisation of a true event, and of ‘armchair detection’, an exercise in pure reasoning. Although set in Paris, the story is actually an account, complete with newspaper reports, of the murder, in New York some years earlier, of Mary Cecilia Rogers. In this story Dupin seeks to arrive at a solution based on close examination of newspaper reports of the relevant facts, without visiting the scene of the crime. The clearest equivalent in Christie is The Thirteen Problems, the Marple collection in which a group of people meets regularly to solve a series of mysteries including murder, robbery, forgery and smuggling. Miss Marple also solves the murders in The Mirror Crack’d from Side to Side basing her solution on the observations of others, and visiting the scene of the crime only at the conclusion of the book; she undertakes a similar challenge in 4.50 from Paddington when Lucy Eyelesbarrow acts as her eyes and ears. Poirot solves ‘The Mystery of Hunter’s Lodge’, in Poirot Investigates, without leaving his sick-bed; and in The Clocks, making what amounts to a cameo appearance, he bases his deductions on the reports of Colin Lamb. For the novels of Christie’s most prolific and ingenious period (roughly 1930 to 1950), the application of pure reasoning applies. From the mid 1950s onwards there was a loosening of the form – Destination Unknown, Cat among the Pigeons, The Pale Horse, Endless Night – and she wrote fewer formal detective stories. But as late as 1964 and A Caribbean Mystery she was still defying her readers to interpret a daring and blatant clue.
The interpretation of a code
Poe’s ‘The Gold Bug’, not a Dupin story, appeared in 1843, and could be considered the least important of his contributions to the detective genre. It involves the solution to a cipher in an effort to find a treasure. A variation on this can be found in the Christie short stories ‘The Case of the Missing Will’ and ‘Strange Jest’, both of which involve the interpretation of a deceased person’s last cryptic wishes. Although the code concept was only a minor part of Christie’s output it is the subject of the short story ‘The Four Suspects’ in The Thirteen Problems. On a more elaborate canvas, the interpretation of a code could be seen as the basis of The A.B.C. Murders; and it is the starting-point of Christie’s final novel, Postern of Fate.
The Trail of false clues laid by the murderer
‘Thou Art the Man’, published in 1844, is not as well known as the other Poe stories but it includes at least two influential concepts, the trail of false clues and the unmasking of the most unlikely suspect. Although a minor theme in many Christie novels, the idea of a murderer leaving a trail of false clues is a major plot device in The A.B.C. Murders and Murder is Easy; and in Towards Zero it is taken to new heights of triple-bluff ingenuity.
The unmasking of the least likely suspect
Like its counterpart above, the unexpected solution, this was a career-long theme for Christie and appears at its most stunning in The Murder of Roger Ackroyd, Hercule Poirot’s Christmas, Crooked House and Curtain. The double-bluff, a regular feature of Christie’s output from her first novel onwards, also comes into this category.
Psychological deduction
Poe’s ‘The Purloined Letter’ pioneered the ideas of psychological deduction and the ‘obvious’ solution. In this type of story, the deductions depend as much on knowledge of the human heart as on interpretation of the physical clues. In Poe’s story Dupin’s psychological interpretation of the suspect allows him to deduce the whereabouts of the missing letter of the title. The Foreword to Christie’s Cards on the Table explains that the deductions in that book will be entirely psychological due to the lack of physical clues apart from the bridge scorecards. And Appointment with Death, set in distant Petra, sees Poirot dependent almost entirely on the psychological approach. Five Little Pigs and The Hollow each have similar emotional and psychological content, although both novels also involve physical clues.
The most obvious solution
Poe’s employment of the ‘obvious solution’ of hiding in plain sight (using a letter-rack as the hiding place of a letter) is adopted, though not as a solution, by Christie in ‘The Nemean Lion’, the first of The Labours of Hercules. The solutions to, for example, The Murder at the Vicarage, Death on the Nile, Evil under the Sun and The Hollow, among others, all unmask the most obvious culprits even though it seems that they have been cleared early in the story and have been dismissed by both detective and reader. In her Autobiography, Christie writes: ‘The whole point of a good detective story is that it must be somebody obvious but at the same time, for some reason, you would find that it was not obvious, that he could not possibly have done it. Though really, of course, he had done it.’
So, Christie’s output adhered to most of the conditions of Poe’s initial model, while simultaneously expanding and experimenting with them. Although Poe created the template for later writers of detective fiction to follow, early in the twentieth century two practitioners formalised the ‘rules’ for the construction of successful detective fiction. But these formalisations, by S.S. Van Dine and Ronald Knox, writing almost simultaneously on opposite sides of the Atlantic, merely acted as a challenge to Agatha Christie’s ingenuity.
S.S. Van Dine’s ‘Twenty Rules for Writing Detective Stories’
Willard Huntington Wright (1888–1939) was an American literary figure and art critic who, between 1929 and 1939, wrote a dozen detective novels under the pen name S.S. Van Dine. Featuring his detective creation Philo Vance, they were phenomenally successful and popular at the time but are almost completely – and deservedly, many would add – forgotten nowadays. Vance is an intensely irritating creation, with an encyclopaedic knowledge of seemingly every subject under the sun and with a correspondingly condescending manner of communication. In The American Magazine for September 1928 Wright published his ‘Twenty Rules for Writing Detective Stories’. Christie knew of S.S.