1. The reader must always have an equal chance along with the detective to solving the mystery. All clues must be openly declared.
2. No willful tricks or pretences may be applied to the reader other than those enacted legitimately by the offender/fugitive on the detective.
3. There can not be a love affair. The job in hand is to apprehend criminal to the bar of justice, not to bring a lovelorn couple to marriage.
4. The detective or investigator themselves should never turn out to be the culprit. This is open deception, on a par with giving some one a penny for a five-pound note. It’s false claims.
5. The accused should be concluded by logical reasoning—not by or assisted by accident or coincidence or unambitious admission. To solve an unlawful enigma in this last fashion is not unlike propelling the reader on a predetermined wild-goose chase, then telling them, after they have failed, that you had the object of their search behind your back all the time. An author like this is no better than a comic.
6. The investigator novel must have a detective in it. An investigator is not an investigator unless he investigates. Their purpose is to gather clues that will eventually lead to the person who did the dirty work in the first chapter. If the investigator does not reach their judgments through an interpretation of those signs, they have not solved the quandary any more than a schoolchild who gets their answers to the time’s table from the side of their pencil case; just like I did.
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 are far too much bother for a misdemeanour other than murder or preferably many murders. The reader’s task and expenditure of energy must be remunerated.
8. The predicament of the offence must be solved by naturalistic means. Methods for discovering the truth as slate-writing, ouija-boards, mind-reading, spiritualistic seances, crystal-gazing, and the like, are all a no-no. A reader has a chance when matching their wits with a rationalistic investigator, but if they must battle with the world of spirits and go chasing about the fourth dimension of metaphysics, they are already defeated before they start.
9. There must be only one investigator—i.e. one protagonist of the deduction. To bring the talents of three or four, or sometimes a gang of investigators to bear on a dilemma, is not only to scatter the interest and break the primary thread of logic but to take an unreasonable advantage of the reader. If there is more than one inspector, how can the reader know who is the protagonist.—I intend to write in First Person Point Of View, as a narration from the protagonist
10. The offender must be a character who has played a noticeable role in the narrative—a person with whom the reader identifies and in whom they take an interest.
11. A servant or butler must not be chosen as the culprit. This is leading to the worst cliche of all “The Butler did it!”
12. There must only be one offender, even if many murders are committed. The accused may, of course, have an insignificant assistant; but the complete onus must rest on one pair of shoulders.
13. The murderer in a detective novel must be given a sporting chance, but it is moving too far to grant them a secret society to drop back on. No self-respecting murderer would desire such odds.
14. The method of killing and the means of detecting it must be intelligent and scientific. Pseudo-science and purely imaginative and speculative devices are not to be allowed. Once an author flies into the kingdom of fantasy, in the Jules Verne manner, they are outside the genre of detective fiction, playing in the undiscovered reaches of adventure.
15. The truth of the puzzle must at all times be plausible—provided the reader is intelligent enough to see it. If the reader, after discovering the explanation for the offence, should reread the book, he would see that the solution had, in a sense, been staring them in the face-that all the evidence pointed to the culprit. That, if he had been as clever as the investigator, he could have solved the mystery crime himself without going on to the final chapter. The fact that a talented reader does often thus determine the problem goes without saying.
16. A detective novel should include no long descriptive paragraphs, no literary dallying with side-issues, no subtly worked-out character analyses, no “mysterious” daydreamings. Such things have no vital place in a record of misconduct and reasoning. They hold up the action and include issues irrelevant to the central purpose, which is to state a quandary, analyse it, and bring it to a victorious conclusion. To be sure, there must be a satisfactory descriptiveness and part delineation to give the novel plausibility.
17. A professional offender must never be shouldered with the guilt of a felony in a detective story. Offenses by housebreakers are the province of the police departments—not of authors and brilliant private investigators. A fascinating crime is one performed by a pillar of a church, or a spinster noted for her compassion.
18. Crime in a detective story need never be an accident or suicide. To end an odyssey of sleuthing with such an anti-climax is to hoodwink the trusting and kind-hearted reader.
19. The goals for all crimes in detective stories should be personal. International plottings and war politics belong in the different category of fiction—in secret-service tales, for example. It must reflect the reader’s everyday experiences, and give them a certain outlet for their own repressed desires and emotions.