There simply must be a corpse in a detective novel, and the deader the corpse the better.
We can probably all agree with this rule from S.S. Van Dine’s 1928 Twenty rules for writing detective stories. Van Dine also frowned on love interests, master criminals, secret societies, twins, hypodermic syringes, knockout drops, seances, coincidence, or servants as the criminal.
And, he says sternly,
A detective novel should contain no long descriptive passages, no literary dallying with side-issues, no subtly worked-out character analyses, no “atmospheric” preoccupations.
Take that, P.D. James, Ruth Rendell and Patricia Highsmith!
Agatha Christie, that unabashed wielder of coincidence and plots cobbled together from the most unlikely chains of events, was a member of The Detection Club, which also included Dorothy L. Sayers, Freeman Wills Crofts and Ronald Knox. Knox was responsible for the club’s “Ten Commandments”, which also ruled out twin brothers, as well as supernatural powers, trapdoors, undiscovered poisons and ‘Chinamen’ (shorthand for exotic foreigners who play by different rules). Writers, take note: no more than one secret room is allowed.
No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right, says Knox. http://www.classiccrimefiction.com/commandments.htm
Does anyone remember the wonderful Derrick in the classic German TV show, whose method was to observe criminals soulfully with his basset-hound brown eyes and read the secrets of their souls? No clues required.
Put Knox’s rule against “unaccountable intuition” with Van Dine’s edict against character analysis and “atmospheric preoccupations,”and you cut quite a swathe through present day detective novels.
Raymond Chandler was a bit dour on the subject. Not a mention of Chinamen, trapdoors or seances.
It must be realistic in character, setting and atmosphere. It must be about real people in a real world.
It must have a sound story value apart from the mystery element: i.e., the investigation itself must be an adventure worth reading.
But by far the most entertaining reading on the subject is G.K. Chesterton’s How To Write a Detective Story:
…the detective story is only a game; and in that game the reader is not really wrestling with the criminal but with the author….
The climax must not be an anti-climax; it must not merely consist of leading the reader a dance and leaving him in a ditch….
The secret may appear complex, but it must be simple…The writer is there to explain the mystery; but he ought not to be needed to explain the explanation. The explanation should explain itself; it should be something that can be hissed (by the villain, of course) in a few whispered words or shrieked preferably by the heroine before she swoons under the shock of the belated realization that two and two make four. Now some literary detectives make the solution more complicated than the mystery, and the crime more complicated than the solution….
What all this goes to show is that it doesn’t much matter what the so-called rules are. Short of the crime of leaving the reader in a ditch, you can get away, literally, with murder.