Rosso agrodolce

    Mystery writer S. S. Van Dine’s twenty rules for writing a good detective novel

1. The reader must have an equal chance with the detective at solving the mystery. All clues must be plainly stated and described.
2. No willful tricks or deceptions may be played on the reader other than those legitimately put over on the detective himself by the criminal.
3. There must not be a love interest that is too engaging. The objective is to bring a criminal before Justice, not two lovers to the altar.
4. Neither the investigator nor any other official police officer must ever turn out to be the culprit. That is foul play: it is like offering someone a shiny copper penny for a gold coin; it is false witness.
5. The culprit must be discovered through logical deduction: not by chance, coincidence, or an unmotivated confession. Solving a criminal problem in such a way is like deliberately sending the reader on a wild goose chase, only to tell them afterward that you had the missing object hidden up your sleeve all along. An author who behaves in this manner is nothing more than a tasteless prankster.
6. In a detective novel, there must be an investigator, and an investigator is no investigator at all if they do not investigate and deduce. Their job is to gather the clues that lead to the capture of the person responsible for the crime committed in Chapter I. If the detective fails to achieve this through such painstaking effort, they have not truly solved the problem—no more than a schoolboy who copies the answer from the back of the math textbook.
7. There must be a corpse in a detective novel, and the deader the corpse the better. No lesser crime than murder will do. Three hundred pages are far too much pother for a lesser crime. The reader’s time and energy must be rewarded!
8. The problem of the crime must be solved by strictly naturalistic means. Such methods for learning the truth as slate-writing, ouija-boards, mind-reading, spiritualistic seances, and crystal-gazing are taboo. A reader has a chance when matching his wits with a rational detective, but if he must compete with the world of spirits and metaphysics, he is defeated ab initio.
9. There must be only one detective in the novel, a single "deducer," a single deus ex machina. Bringing three, four, or an entire pack of sleuths onto the stage to solve the case not only scatters interest and breaks the thread of logic, but also claims an unfair advantage over the reader. If there is more than one detective, the reader no longer knows whom they are competing against; it would be like entering a lone runner into a relay race.
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 a rule, as the culprit. That is too easy a solution. The culprit must decidedly be a worthwhile person—someone who would not ordinarily come under suspicion.
12. In the novel, there must be only one culprit, regardless of the number of murders. The culprit may naturally make use of accomplices, but the guilt and the reader’s indignation must fall upon a single villain.
13. Secret societies, criminal syndicates, and the like have no place in a true detective novel. A compelling crime is irreparably ruined by collective guilt. To be sure, the culprit must be granted a "sporting chance"; but granting them an entire secret society is far too much. No high-class criminal would ever accept it.
14. The criminal's methods and the systems of investigation must be rational and scientific. That is to say, pseudoscience and purely fantastical devices in the style of Jules Verne must be entirely ruled out. When an author resorts to such measures, they may consider themselves to have broken out from the bounds of the detective novel and fled into the uncharted realms of the adventure story.
15. The truth of the problem must be apparent at all times, provided a reader is shrewd enough to see it. By this I mean that if the reader, after reaching the explanation, should reread the book, he would see that the solution had, in a sense, stared him in the face—that all clues pointed to the culprit, and that, had he been as clever as the detective, he could have solved the mystery himself without going on to the final chapter. And that, needless to say, often happens to the well-read reader.
16. A detective novel must not contain overly sprawling descriptions, literary flourishes, excessively labored psychological analyses, or atmospheric scene-setting: these are all matters of no vital importance to a detective novel. They slow down the action and distract from the primary purpose, which is to pose a problem, analyze it, and bring it to a successful conclusion. Naturally, there must be just enough description and character study to lend verisimilitude to the story.
17. A professional criminal must never be chosen as the culprit in a detective novel. The crimes of housebreakers and bandits belong to the police department, not to authors and brilliant amateur detectives. A truly fascinating crime is one committed by a pillar of the church, or an old maid known for her charitable deeds.
18. The crime in a detective novel must never turn out to be an accident, nor should it ever be revealed as a suicide. To wind up an odyssey of an investigation with such an anti-climax is to play an unforgivable trick on the trusting and gentle reader.
19. The motives for all crimes in detective stories should be personal. International plots and the like belong to a different genre of fiction. A detective story must reflect the reader's everyday experiences, serving as a safety valve for his own emotions.
20. And here, in conclusion, to properly round out this "credo," is a list of devices that no self-respecting detective writer will ever resort to again, because they have been overused and are now familiar to every detective fiction enthusiast. To employ them is a confession of ineptitude and a lack of originality:
    • Determining the culprit by comparing a cigarette butt left at the scene of the crime with the brand smoked by a suspect;
    • The bogus spiritualistic seance to frighten the culprit into giving himself away;
    • Forged fingerprints;
    • The dummy-figure alibi;
    • The dog that does not bark, thereby revealing that the culprit is a familiar member of the household;
    • The culprit turning out to be a twin, or a look-alike relative of a suspected but innocent person;
    • Hypodermic syringes and knock-out drops;
    • The commission of the murder in a locked room after the police have already broken in;
    • Word association tests that reveal guilt;
    • A cipher or code letter that the detective deciphers.