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I just was reading S.S. Van Dine's 1928 manifesto on "Twenty rules for writing detective stories" and immediately parallels to adventure writing/running sprang to mind for DMs. I am an admitted fan of the whole mystery genre, but as I'm sure many DMs and players will attest they don't always play smoothly at the table. The players misinterpret, ignore, or utterly miss clues, and generally lolly gag while forgetting key NPC names and refusing to write anything down. The DM railroads the players to get back on track, and is indignant that the players could have missed something "so obvious" or is left scratching his or head when the genre-savvy players guess the villain fresh out of the gate.
Do any of these ring true for your group?
Obviously, D&D is not GUMSHOE. It's fantasy adventure, not hardboiled detective roleplay. But that doesn't mean a DM can't learn from the likes of the Canary Murder Case.
Here is an interpretation of the twenty points (from http://gaslight.mtroyal.ca/vandine.htm) for DMs:
A more appropriate analogue might be that the murder/crime must be definable in game terms. If it was murder-by-spell, then that spell needs to be written up and should be able to be guessed at thru examining effect, component remnants, etc.

For example, (f) is clearly the use of a doppelgänger or other shapeshifter as the villain disguised as another NPC / PC.
Do any of these ring true for your group?
Obviously, D&D is not GUMSHOE. It's fantasy adventure, not hardboiled detective roleplay. But that doesn't mean a DM can't learn from the likes of the Canary Murder Case.
Here is an interpretation of the twenty points (from http://gaslight.mtroyal.ca/vandine.htm) for DMs:
This brings to mind Robin Laws in GUMSHOE where the core clues are automatically delivered when the PCs investigate a certain scene or witness. Substitute player for 'reader' and character for 'detective' and it is clear that a mystery needs to challenge the players and not just their characters.1. The reader must have equal opportunity with the detective for solving the mystery. All clues must be plainly stated and described.
This one is pretty straight-forward. In D&D terms I would say you also want to avoid red herrings in adventure prep.2. No willful tricks or deceptions may be placed on the reader other than those played legitimately by the criminal on the detective himself.
Another straight-forward one that is more a reflection of S.S. Van Dine's personal biases.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.
This one makes sense, and frankly it would be hard to pull off an investigation of a PC-committed crime unless extraordinary measures were taken or it's the old "evil PC in a party of good PCs" schtick. Probably both are best avoided.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.
I interpret this as the DM should allow that failure is possible, and not just lead the rambling and confused players to the truth with a throwaway encounter. The PCs may fail to solve the mystery, and that has to be prepared for with a Fail Forward. Without the risk of failure, success is less meaningful.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.
Maybe the closest analogy in a D&D session is to having player buy-in that they're going to be playing in a mystery adventure. It's not to say that players should abandon their out-of-the-box ideas to sacrifice them on some altar of "genre appropriateness", but realizing that brute force won't solve a mystery is a good realization that will guide how they approach the session.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.
Good old S.S. Van Dine shows another of his biases here. In D&D, if there's a corpse in a mystery scenario, you can bet that the PCs will bring some kind of forensic magic to bear, so a DM needs to know what sorts of spells/rituals are common and at the party's disposal, and be prepared to answer those. This ties into a later point about understanding how the crime was executed in vivid detail.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.
The takeaway from this is that a mystery needs to be constructed so that no single divination spell will ruin the entire mystery, and even better that no battery of Divinations will reveal the whole mystery. Let them be a useful tool in the players' toolbox, but not an "I win" button. Accomplish this by understanding the Divinations available at the party's level and what their limitations are. For example, a speak with dead spell will learn little from a man struck from behind or shot at range or stabbed in the dark or who faced a masked assailant.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 se'ances, 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.
Obviously, D&D breaks this rule by its very nature. However, just as old dungeon crawls used to designate one player as the "caller", one as the "mapper", and so on, you might have one player be the "detective" who takes notes on the investigation. This could be a player who is more naturally drawn to mysteries or it could be a player whose PC is intimately connected to the crime or victim.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.
I take this one to imply the PCs need to meet the villain at some point before they know he or she is the villain, and have a chance to interrogate him or her. The important thing he is not to tip your hand and remember what the mystery is about. If the villain is noble and the mystery is about the methods and proving a case in court, then knowing who the villain is won't do the players much good - they still need to figure out how he did it and get that evidence. OTOH if the mystery is about identifying the villain and the PCs have carte blanche to deal with him/her as they see fit, then be very careful with the villain's answers. Dissembling - evading the truth by answering a different question than was asked, or bating the or distracting the PCs - is an exceptional tactic during any kind of questioning. Truth detecting magic should bear a social onus; and if done without permission should be grounds for hostility or legal action. Also bear in mind that the more convoluted the mystery is, the harder it is to know which are the right questions to ask until one has investigated it to a certain depth.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.
Another curious bias that reflects the time S.S. Van Dine was writing in! I would say be aware of any biases or suspicions the players bring to the table. For example, if your last game featured a noble as the doppelgänger, they are going to be suspicious of nobles. It doesn't make sense. That's how players are. They will game the DM, so be aware of your patterns and break them with relish.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.
There needs to be a villain, that's pretty much always true. Where this gets fun is when the person doing the wetwork/crime is different than the one ordering the hit/crime. In D&D this could even include crimes committed while under a charm spell.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.
Another curious bias. Certainly mafias and secret societies can be used to great effect as potential suspects for the PCs to investigate. And they can feature as main villains too. I think the point here is that if you have just one really bad guy or organization, then it's easy for the players to glom onto that one as THE BBEG of the adventure. One solution is to have a whole network of scheming NPCs who operate in a morally grey setting. This makes anyone who is wholly altruistic or honest immediately suspect.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.
Of course, D&D thrives in the uncharted reaches of adventure!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.

This gets back to the idea that the clues need to absolutely point to the conclusions that need to be drawn to solve the mystery. As a corallarly, the Three-Clue Rule is a good point to remember; for every conclusion you want the players to reach, there need to be three clues scattered in the adventure because the players will miss the first, ignore the second, and misinterpret the third15. 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.

To me, this is a call against boxed text or the DM stealing the limelight from the players. Good advice, in general.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.
This is a really good point. While a professional criminal may be included in the list of suspects, the players' quarry needs to be someone who wouldn't normally be suspected or who is above the law (but not above getting taken down by adventurers).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.
This one makes sense and seems straight-forward enough to me. Ancillary deaths connected to the main crime could certainly be accidental or tragic, but the main crime needs a certain cruel intention behind it to evoke pathos in the players & make them want to solve it.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.
I had to look up gemütlich - basically it means personal, or human-scale. And even if there are war politics behind the crime, there should always be something personal behind it. That's how you assemble a list of suspects, from some common motive. A slight terseness in an NPC's voice alerts the PCs that they don't care for the Duke. It's the human/emotional element that engages players and makes the villain more believable and either sympathetic, tragic, or hated.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 gemütlich, so to speak. It must reflect the reader's everyday experiences, and give him a certain outlet for his own repressed desires and emotions.
This is a great list! It would be fun to come up with something analogous for D&D adventures, a sort of collection of trite stereotypes that immediately alert the players to foul play.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 se'ance 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.
For example, (f) is clearly the use of a doppelgänger or other shapeshifter as the villain disguised as another NPC / PC.