The Ten Commandments of Detective Fiction

• 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.
• All supernatural or preternatural agencies are ruled out as a matter of course.
• Not more than one secret room or passage is allowable.
• No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
• No Chinaman must figure in the story.
• No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
• The detective must not himself commit the crime.
• The detective must not light on any clues which are not instantly produced for the inspection of the reader.
• The stupid friend of the detective, the Watson, must not conceal any thoughts which pass through his mind; his intelligence must be slightly, but very slightly, below that of the average reader.
• Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.

PS: Here is the oath, composed by G. K. Chesterton, of membership in the famous British Detection Club: "Do you promise that your detectives shall well and truly detect the crimes presented to them using those wits which it may please you to bestow upon them and not placing reliance on nor making use of Divine Revelation, Feminine Intuition, Mumbo Jumbo, Jiggery-Pokery, Coincidence, or Act of God?"

REVISED VERSION
This is presumptuous, but here is Grobius Shortling's Revised Version:

• The criminal must be somebody mentioned in the story. (This is absolutely essential, otherwise the book cannot be called a detective story. The other bit about 'sharing thoughts' is too strict, but a writer should still be cautious because an outright authorial deception must be avoided.)
• Supernatural elements are allowable for atmospheric or plot reasons, but they must play no part in the actual solution of the mystery.
• Secret passages or hidden rooms are all right (if the setting allows it), but do not deserve to be used as an explanation of the murder method.
• Avoid unknown Amazonian arrow poisons or newly invented Death-Ray machines, unless as an author you are qualified (scientifically) to justify it (i.e., if Newton had written a mystery based on his laws of Optics, that would be OK, but don't presume to invent a poison if you don't even know that aspirin can be fatal.)
• Do not use 'foreigners' or other aliens as major characters unless you have some real understanding of their culture and mind-set, and they have some relevance to the plot beyond exotic obfuscation.
• Avoid accidental solutions, as they are hardly fair in a story of deduction and the presentation of real clues. And please do not inflict on the poor reader one of those mid-book "Mon dieu, how could I not have seen that before" exclamations which sit like undigested food until the end of the mystery.
• The criminal should not be someone you have intentionally presented as totally trustworthy. (If he/she is a liar, at least provide some clue to give the reader a chance to spot that.)
• All clues must be revealed, although it is perfectly legitimate to disguise them. (But I would draw the line at basing a clue on some misspelling of a word, American vs. British usage, for example, because most books are hardly proofread any more.)
• There should but doesn't have to be a 'Watson' or some observing point of view that sees but misinterprets the events under investigation. (Only common sense, otherwise where is the drama?)
• Do not try to fool the reader with improbable impersonations, such as a woman posing as a man or vice versa and getting away with it by consummate acting ability, especially when they are deceiving people who know them well. (This doesn't even work in Shakespeare.) Especially avoid wigs and false whiskers!

TEN MORE COMMANDMENTS
A few more caveats based on this reviewer's prejudices (another 10 Commandments):

• Do not try to confuse the reader with elaborate timetables based on train schedules, etc., as there is no guarantee that things like that would ever work out for even the carefullest murderer. (Sod's or Murphy's Law.)
• Avoid having your Prime Suspect turn out to be the culprit after all, because this is ultimately disappointing (unless you are clever enough to totally reshuffle motives and alibis).
• Do not present an 'impossible crime' situation without at least attempting to verify its plausibility by experiment. Also try to avoid using an accomplice to abet the criminal's illusion. (That's OK for stage magicians with their assistants, but spoils a mystery plot where the villain has to deceive the detective, almost, but without cheating. It makes a lot of sense, too, if you are a villain, not to risk collaboration.)
• The murderer should never turn out to be somebody incapable of committing the crime, at least as presented in the lead-up (i.e., invalids in wheelchairs, morons, a person in an intensive-care ward, an astronaut who happened to be in orbit at the time).
• A conspiracy involving a hired hit-man, or a mysterious Illuminati cartel, does not belong in a true detective novel. This also includes situations where several suspects are independently up to no good and just happen to be on the scene at the relevant time. (Sod's Law, again, and a very mechanical manipulation of coincidence for supposedly dramatic purposes -- this won't fool anybody and should be dismissed as mere padding.)
• No faking of fingerprints or other forensic details. In spite of their portrayal, even the police a hundred years ago were not as incompetent as they were made out to be. Nowadays, if you want to commit a murder, forget trying such a thing, unless you can afford a good lawyer to screw up the expert witnesses at your trial!
• If you are going to talk down to the reader (who is an ignoramus, whereas you are a genius), via your detective, make sure your facts are correct. Twaddle about Egyptology (curse of the pharaoh, etc.) is unacceptable. Informative facts about some obscure subject, however, are beneficial.
• Do not present your detective as an ineffectual fool or allow him or her to show any signs of not being superior to the reader or the 'Watson' (except to the extent that the detective can have misjudgements and miscalculations for the sake of 'bonding' with the reader). An incompetent detective is an actor in a comedy, not a detective story.
• Get your details of real police policies and forensic science up to date as far as you can. Unless the book takes place in the classic stranded house-party tradition, there is no way an author can get away with ignoring public procedures, no matter how gifted the detective.
• Finally, a personal peeve: Don't have a large cast of characters and refer to them all by their Christian names, such as Evelyn, Jane, Meg, Charles, and Chris. Who in the hell are you talking about?

Grobius Shortling (July 4, 2001)

HOWARD HAYCRAFT'S RULES
A classic readers' guide was published in 1941 (Murder for Pleasure © renewed 1968 Howard Haycraft) and while dated is one of the best treatises on the subject. Haycraft's "Rules of the Game" chapter expounds in greater detail than a simple decalogue. Here are the sub-sections (paraphrased or reinterpreted, not quoted in full -- just to provide the flavor):

• Structure and Sources: Mainly keep in mind that the plot comes first and that the actions of the characters are 'retrofitted' into it, which is how a detective story differs from a crime novel where of course the characters themselves drive the plot. Any central pivot, such as an expertise about some unusual subject, is up to the author -- as long as it is accurate.
• The Need for Unity: In other words, make the story fit the devised crime. A person -- detective, suspect, witness -- should not act out of 'character' just because the plot demands it. In that case, it is better just to redesign the character.
• The Detective: This is almost axiomatic -- one must have a detective who is distinctively defined, preferably a series detective (which saves having to create a new one for each book -- easier that way both for the writer and the reader and engenders a familiarity that ensures comfort and a market for new books). Initially defining a detective whom readers can 'identify' with as a familiar friend is one of the hardest things, apart from plotting, for a detective novelist to do, but once done removes the burden of re-explication.
• Watson or Not?: Discouraged now because it is trite, but if you have to have one, make him a total opposite of the detective -- e.g., Archie Goodwin vs Nero Wolfe.
• Viewpoint: Standard literary practice, whatever the genre. There has to be a consistency of delivery for the story, no matter what technique is used (first person, omniscient, point-of-view, whatever).
• The Crime: There really must be a murder, or at least a major felony -- otherwise, what's the point? Who's ripping off the hand towels at the Dorchester Hotel is hardly the business of a mystery novel.
• The Title: "The best advice to the author faced with the selection of a title is not to worry about it." Having a good title and basing the book on it is like the tail wagging the dog. 'Nuff said.
• The Plot: Keep it flowing from one thing to another and don't get sidetracked into dead-ends. Well, that's common sense for all fiction.
• "Had I But Known": That has always been a bugaboo among mystery fans since Mary Roberts Rinehart and earlier. It is the ditzy heroine sneaking into Bluebeard's chamber even if she has been repeatedly warned not to. It is the kid's action when told "Whatever you do, don't climb on the railway tressle." Does not belong in a detective story. (Can be fun enough in a gothic romance or horror novel or something of the sort.)
• Emotion and Drama: Of course for dramatic reasons there has to be some of this for the sake of interesting the reader, but for the most part remember that this is a novel of detection, not a love story.
• The Puzzle Element: Don't make that the whole story; this is not a crossword puzzle.
• Background and Setting: Basically, the author should be familiar personally with the location. If you were in Aruba for three hours on a cruise ship trip, don't set your novel in Aruba based on that. Use real settings when possible, for verisimilitude, and be accurate. And, PS, don't borrow somebody else's setting, such as Wuthering Heights.
• Characters and Characterization: Not all of the players need to be fully defined -- puppet roles are fine (cops, servants, etc.) -- but at least the detective, the murderer, and preferably the victim should be convincingly realized. Is this obvious or what? But a lot of formula mysteries totally ignore this precept.
• Style: Avoid corniness, pretentiousness, and overwriting. (Duh...)
• The Devices of Detection: Don't be so elaborate as to make the dénouement incomprehensible. Beware of ignorance of the simple rules of evidence and forensics. (Then follows a whole list of things to avoid, like tobacco ashes, locked rooms, footprints, etc., but that is just HH's judgment based on what were clichés then. If it works, then it's OK, right?)
• Physical Boundaries: This is basically advice on how long a mystery novel or story should be. Times change -- sometimes very lengthy, sometimes very short, now lengthy again (because of the high cover cost of a book these days -- padding out an extra couple hundred pages, which isn't that more expensive production-wise, makes the reader think it's worth the money).
• Some General Considerations: Basically extols the existence of bodies like The Detection Club in England, which encouraged new ventures in this genre, and was a professional forum for both established and hopeful writers. MWA encourages this now in the US (but not so much back then).

THE DETECTIVE story is a kind of intellectual game. It is more -- it is a sporting event. And for the writing of detective stories there are very definite laws -- unwritten, perhaps, but none the less binding; and every respectable and self-respecting concocter of literary mysteries lives up to them. Herewith, then, is a sort Credo, based partly on the practice of all the great writers of detective stories, and partly on the promptings of the honest author's inner conscience. To wit:

1. The reader must have equal opportunity with the detective for solving the mystery. All clues must be plainly stated and described.
2. No willful tricks or deceptions may be placed on the reader other than those played legitimately by the criminal on the detective himself.
3. There must be no love interest. The business in hand is to bring a criminal to the bar of justice, not to bring a lovelorn couple to the hymeneal altar.
4. The detective himself, or one of the official investigators, should never turn out to be the culprit. This is bald trickery, on a par with offering some one a bright penny for a five-dollar gold piece. It's false pretenses.
5. The culprit must be determined by logical deductions -- not by accident or coincidence or unmotivated confession. To solve a criminal problem in this latter fashion is like sending the reader on a deliberate wild-goose chase, and then telling him, after he has failed, that you had the object of his search up your sleeve all the time. Such an author is no better than a practical joker.
6. The detective novel must have a detective in it; and a detective is not a detective unless he detects. His function is to gather clues that will eventually lead to the person who did the dirty work in the first chapter; and if the detective does not reach his conclusions through an analysis of those clues, he has no more solved his problem than the schoolboy who gets his answer out of the back of the arithmetic.
7. There simply must be a corpse in a detective novel, and the deader the corpse the better. No lesser crime than murder will suffice. Three hundred pages is far too much pother for a crime other than murder. After all, the reader's trouble and expenditure of energy must be rewarded.
8. The problem of the crime must he solved by strictly naturalistic means. Such methods for learning the truth as slate-writing, ouija-boards, mind-reading, spiritualistic seances, crystal-gazing, and the like, are taboo. A reader has a chance when matching his wits with a rationalistic detective, but if he must compete with the world of spirits and go chasing about the fourth dimension of metaphysics, he is defeated ab initio.
9. There must be but one detective -- that is, but one protagonist of deduction -- one deus ex machina. To bring the minds of three or four, or sometimes a gang of detectives to bear on a problem, is not only to disperse the interest and break the direct thread of logic, but to take an unfair advantage of the reader. If there is more than one detective the reader doesn't know who his codeductor is. It's like making the reader run a race with a relay team.
10. The culprit must turn out to be a person who has played a more or less prominent part in the story -- that is, a person with whom the reader is familiar and in whom he takes an interest.
11. A servant must not be chosen by the author as the culprit. This is begging a noble question. It is a too easy solution. The culprit must be a decidedly worth-while person -- one that wouldn't ordinarily come under suspicion.
12. There must be but one culprit, no matter how many murders are committed. The culprit may, of course, have a minor helper or co-plotter; but the entire onus must rest on one pair of shoulders: the entire indignation of the reader must be permitted to concentrate on a single black nature.
13. Secret societies, camorras, mafias, et al., have no place in a detective story. A fascinating and truly beautiful murder is irremediably spoiled by any such wholesale culpability. To be sure, the murderer in a detective novel should be given a sporting chance; but it is going too far to grant him a secret society to fall back on. No high-class, self-respecting murderer would want such odds.
14. The method of murder, and the means of detecting it, must be be rational and scientific. That is to say, pseudo-science and purely imaginative and speculative devices are not to be tolerated in the roman policier. Once an author soars into the realm of fantasy, in the Jules Verne manner, he is outside the bounds of detective fiction, cavorting in the uncharted reaches of adventure.
15. The truth of the problem must at all times be apparent -- provided the reader is shrewd enough to see it. By this I mean that if the reader, after learning the explanation for the crime, should reread the book, he would see that the solution had, in a sense, been staring him in the face -- that all the clues really pointed to the culprit -- and that, if he had been as clever as the detective, he could have solved the mystery himself without going on to the final chapter. That the clever reader does often thus solve the problem goes without saying.
16. A detective novel should contain no long descriptive passages, no literary dallying with side-issues, no subtly worked-out character analyses, no "atmospheric" preoccupations. Such matters have no vital place in a record of crime and deduction. They hold up the action and introduce issues irrelevant to the main purpose, which is to state a problem, analyze it, and bring it to a successful conclusion. To be sure, there must be a sufficient descriptiveness and character delineation to give the novel verisimilitude.
17. A professional criminal must never be shouldered with the guilt of a crime in a detective story. Crimes by housebreakers and bandits are the province of the police departments -- not of authors and brilliant amateur detectives. A really fascinating crime is one committed by a pillar of a church, or a spinster noted for her charities.
18. A crime in a detective story must never turn out to be an accident or a suicide. To end an odyssey of sleuthing with such an anti-climax is to hoodwink the trusting and kind-hearted reader.
19. The motives for all crimes in detective stories should be personal. International plottings and war politics belong in a different category of fiction -- in secret-service tales, for instance. But a murder story must be kept gemuctlich, so to speak. It must reflect the reader's everyday experiences, and give him a certain outlet for his own repressed desires and emotions.
20. And (to give my Credo an even score of items) I herewith list a few of the devices which no self-respecting detective story writer will now avail himself of. They have been employed too often, and are familiar to all true lovers of literary crime. To use them is a confession of the author's ineptitude and lack of originality. (a) Determining the identity of the culprit by comparing the butt of a cigarette left at the scene of the crime with the brand smoked by a suspect. (b) The bogus spiritualistic seance to frighten the culprit into giving himself away. (c) Forged fingerprints. (d) The dummy-figure alibi. (e) The dog that does not bark and thereby reveals the fact that the intruder is familiar. (f)The final pinning of the crime on a twin, or a relative who looks exactly like the suspected, but innocent, person. (g) The hypodermic syringe and the knockout drops. (h) The commission of the murder in a locked room after the police have actually broken in. (i) The word association test for guilt. (j) The cipher, or code letter, which is eventually unraveled by the sleuth.