RPG Evolution: The Fair-Play Whodunnit

The rules for a fair-play whodunnit can make for a fun investigative adventure.

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Who Done What?​

Although they've since fallen out of vogue, fair-play whodunnits were quite popular with early detective fiction of the 1930s. The term refers to mystery stories where the reader or audience is given all the necessary clues and information to solve the crime alongside the detective. In a fair-play whodunnit, the emphasis is on the puzzle-solving aspect of the mystery. The term "fair-play" indicates that the mystery adheres to a set of rules that ensure the reader has a fair chance of deducing the identity of the culprit before the big reveal.

Fair-play whodunnits lend themselves to role-playing campaigns because they are meant to be solvable. The detectives, whether amateur or professional, must use their intellect, observational skills, and logical reasoning to piece together the clues and unravel the truth behind the crime. The story presents a series of tantalizing clues, hidden motives, and potential suspects, inviting players to engage in the investigation themselves.

The Ten Commandments of Fair-Play​

In 1928, the writer Father Ronald Knox created a list of plot devices known as Knox's Decalogue. These rules still apply today, but require some tweaking to apply them to fantasy campaigns.
  1. The Criminal: In the Fair-play Whodunnit, the culprit must be introduced early in the story, but their inner thoughts should remain hidden from the reader or players. In a D&D campaign, DMs can introduce NPCs who become suspects in the mystery. However, the true perpetrator should be hidden, with their motives obscured until the climactic reveal.
  2. No Supernatural Agencies: The use of supernatural or preternatural elements is discouraged in Fair-play Whodunnits. In a fantasy D&D setting, this translates to avoiding the use of overtly magical means to commit the crime. Instead, focus on mundane methods amplified by magical twists or disguise spells. In other words, internal logic is a must -- if a spell is used, the PCs should have access to it or known how it's cast. Some older movies exercise several plot contortions to avoid breaking this rule, but for fantasy campaigns the game's rules provide something of a guideline. Conversely, a villain shouldn't use a spell that isn't in the rules.
  3. Limited Secret Passages: Fair-play whodunnits relied heavily on sneaking around, providing seemingly magical routes for villain to appear and disappear from the screen. While only one secret passage is allowed in the Fair-play Whodunnit, DMs can adapt this rule by introducing enchanted doorways or teleportation circles within suitable locations. And remember, if the villain can use it, so can the PCs!
  4. No Undiscovered Poisons: Like secret passages, mystery authors were fond of adding undetectable, instantly lethal poisons to their plots to make it nearly impossible for authorities to determine the identity of the killer. In a fantasy setting, DMs can use rare or magical poisons that already exist in the rules, but should avoid creating new poisons that nobody's ever heard of.
  5. Avoid Clichés and Stereotypes: The original Knox's Decalogue prohibits the use of certain ethnic stereotypes. In a D&D campaign, avoid using fantasy equivalents, such as clichéd species, to prevent perpetuating harmful tropes. This is often played against type (everyone suspects the dwarf of poisoning someone, or the elf of casting a spell).
  6. No Detective Accidents: Ensure that the detective's discoveries are the result of clever deduction and not fortunate accidents. In a D&D campaign, the detective skills of a player character should lead to the uncovering of vital clues rather than coincidental discoveries -- or DM fiat.
  7. No Detective as the Culprit: As in the original rules, the detective cannot be the culprit in a Fair-play Whodunnit. In a D&D campaign, this means keeping player characters free from suspicion, allowing them to focus on solving the mystery. It's tough to make them out to secretly be villains in any case.
  8. Instant Clue Reveal: Clues should be readily available for players to inspect. In a D&D campaign, ensure that players have access to all the clues needed to solve the mystery, but challenge them with cleverly hidden or magically disguised information.
  9. The NPC's Mind: The "Watson" character, typically a foil for the lead detective, should be open and transparent in their thoughts. In a D&D campaign, this can be an NPC or a player character who assists the party. Their capabilities should be slightly below the average player's, allowing players to feel engaged and challenged by the investigation.
  10. Prepare for Doubles: In a fantasy setting, "doubles" can take the form of doppelgangers or magical clones. Ensure that their existence is foreshadowed to avoid surprising players with unexpected duplications.
We discuss fifty of these types of dramas in our recently-released podcast, 50 Date Night Screams, along with D&D statistics for each major villain. Although these rules are decades old, they still apply to fashioning a mystery that heroes (and by proxy, their players) can figure out on their own.

Your Turn: What guidelines do you use for solving mysteries in your game?
 

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Michael Tresca

Michael Tresca


EzekielRaiden

Follower of the Way
I did more or less this (much less formally, of course) with a whodunnit mystery. The one "not quite there" thing I did was that I said the victim--whom the party Ranger(with Cleric spells) revived--wouldn't be able to help identify the killer because the manner of their death had scrambled their memories of the time before said death. (Also, because the player rolled only a partial success, it would take the victim time to fully revive.)

There were clues hidden in plain sight, and difficulties to overcome. For example, I leveraged the fact that one of my players studied physical anthropology. Player knows that bodies take time before they achieve livor mortis--the pooling of the blood in the lower extremities. But the body, mere minutes after being found with a knife in its back, had not bled all over the place. Indicating, as this player (and character) well knew, that the body had been staged and the death occurred several hours earlier. But that was contradictory information--people had seen the victim at the masquerade ball only an hour before, getting into a row with a visiting dignitary! Clearly all was not as it seemed...and someone had the ability to disguise themselves as the victim in order to throw them off the scent.

Things proceeded from there and the players were able to get all of the information and catch the true culprit. All in all, an excellent little adventure along the way. I haven't done any "murder mystery" type adventures since--feels like it would be a bit repetitive if I did. But there are other investigations that can be similarly "whodunnit" without being murders.
 


In addition to Knox's Decalogue, I would be remiss as an Umineko fan if I didn't also recommend the (significantly more verbose) Twenty Rules for Writing Detective Stories by S. S. Van Dine:

  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 someone 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 conclusion through an analysis of those clues, he has no more solved the 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 be 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 co-dedutcor 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 too easy a 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 irredeemably spoiled by any such wholesome 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 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 house-breakers and bandits are the province of police departments - not of authors and brilliant amateur detectives. A really fascinating crime in 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 of a suicide. To end an odyssey of sleuthing with such and 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 gemuetlich, 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 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 the 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 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.

Which reminds me, I need to go see a witch about some gold...
 


EzekielRaiden

Follower of the Way
I think the biggest sin in may adventures, mystery or otherwise, is the "Roll to Countinue". Something vital requires the players succeed on a roll otherwise the adventure can't be completed. This might be a clue, a secret door, tracks, etc.
Frankly, it's one of the bigger sins in GMing generally.
 

EzekielRaiden

Follower of the Way
Rule 7 and 9: I guess no one told Agatha Christie...
It's worth noting, she only did #7 once, and it was rather clearly a major subversion. It received good reviews, to be fair, but it's also a controversial move.

Not sure when she violated #9 though? Unless you mean the same story, which would mean it couldn't be #7 (since the Watson-alike, the Detective's Assistant, is distinct from the Detective character.)
 

It's worth noting, she only did #7 once, and it was rather clearly a major subversion. It received good reviews, to be fair, but it's also a controversial move.
Twice.
Not sure when she violated #9 though? Unless you mean the same story, which would mean it couldn't be #7 (since the Watson-alike, the Detective's Assistant, is distinct from the Detective character.)
Spoiler: a certain long running play that I'm not allowed to talk about.

Gladys Mitchell broke that one too.
 

Rule 7 and 9: I guess no one told Agatha Christie...
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Additionally, the Agatha Christie book in question (or the predominant one that comes to mind...my collection is far from complete) - The Murder of Roger Ackroyd - was published in 1926, while Knox's Decalogue is generally dated to around 1929 (and Van Dine's Rules to 1928), so it's likely that on some level those rules were created in response to Christie, rather than Christie deliberately subverting them.
 
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payn

He'll flip ya...Flip ya for real...
I follow many of the guidelines above, but I also give much thought to the culprit. The best way to show my method is to point to a Law and Order: Criminal Intent episode. For those unfamiliar, a crime is shown being committed, then the investigators begin, and the culprits react until caught. In many traditional portrayals, the audience is only given the experience of the investigator. In RPGs, IME, many GMs leave things static as the PCs solve the crime. Its a different medium than literature or film, so I do not, of course, give the PCs the NPC culprits mind. However, the culprit will be taking either proactive or reactive measures, and often both, as the puzzle unfolds.
 

talien

Community Supporter
One of the biggest problems I have with a lot of expansive fiction, like Star Trek or the Marvel Cinematic Universe, is that when there are god-like characters, I begin to question fundamentals and therefore anything is possible. That is, once I know doppelgangers exist, they can be behind everything and everyone. Once I know you can create an undetectable poison once, I assume it can be every time.

You'll often see that there's some sort of scan to "prove" that this isn't the case, and that's basically a fictional backstop so the audience can stop guessing if magic/aliens/etc. are the reason behind the mystery. Similarly, D&D's best bet is trueseeing in some form (be it spell or ability), but players have to take it on faith that if the DM says "this is not the result of time travel or shapeshifitng" that they believe it.

Murder mysteries work because there's logic to the universe. Push it too far and PCs don't know what to believe anymore and aren't particularly vested in determining the outcome because anything is possible.
 

payn

He'll flip ya...Flip ya for real...
One of the biggest problems I have with a lot of expansive fiction, like Star Trek or the Marvel Cinematic Universe, is that when there are god-like characters, I begin to question fundamentals and therefore anything is possible. That is, once I know doppelgangers exist, they can be behind everything and everyone. Once I know you can create an undetectable poison once, I assume it can be every time.

You'll often see that there's some sort of scan to "prove" that this isn't the case, and that's basically a fictional backstop so the audience can stop guessing if magic/aliens/etc. are the reason behind the mystery. Similarly, D&D's best bet is trueseeing in some form (be it spell or ability), but players have to take it on faith that if the DM says "this is not the result of time travel or shapeshifitng" that they believe it.

Murder mysteries work because there's logic to the universe. Push it too far and PCs don't know what to believe anymore and aren't particularly vested in determining the outcome because anything is possible.
I think thats why I took a moment to say literature/film is different than RPGs. Where McGuffins and God like characters are usually contained by the narrative of the storytelling, RPGs dont exist in a vacuum. It's also why I dont tend to like high level play because it makes classic themes like whodunnit a total PITA to pull off on the table.
 


rknop

Adventurer
I think the biggest sin in may adventures, mystery or otherwise, is the "Roll to Countinue". Something vital requires the players succeed on a roll otherwise the adventure can't be completed. This might be a clue, a secret door, tracks, etc.

The recognition of that sin in investigative scenarios is cited as one of the driving forces behind the creation of Pelgrane's "Gumshoe" system (used in Trail of Cthulhu, Swords of the Serpentine, Timewatch, Night's Black Agents, and others).
 

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Additionally, the Agatha Christie book in question (or the predominant one that comes to mind...my collection is far from complete) - The Murder of Roger Ackroyd - was published in 1926, while Knox's Decalogue is generally dated to around 1929 (and Van Dine's Rules to 1928), so it's likely that on some level those rules were created in response to Christie, rather than Christie deliberately subverting them.
There can be little doubt that they where written in response to the huge success of Agatha Christie's first novel. "These women have no business writing about murder, don't they know it's a man's subject!? The don't even play by the rules! The should stick to soppy romance!"

I think Christie's view of them can be surmised by the fact that she used the same ploy again in Endless Night (1967).
 

Are Agatha Christie novels supposed to be Fair-Play Whodunnits? I thought they were regular crime novels, but I've never read any so I don't know.
I don't think any of the top mystery writers took these rules seriously. And of course Doyle, Collins and Poe predate them.

All of the Christie mysteries* are "solvable by the reader" before the detective announces the correct solution though.


*Not all her stories are mysteries. Some are more action/adventure/spy/comedy/romance.
 
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There can be little doubt that they where written in response to the huge success of Agatha Christie's first novel. "These women have no business writing about murder, don't they know it's a man's subject!? The don't even play by the rules! The should stick to soppy romance!"

I think Christie's view of them can be surmised by the fact that she used the same ploy again in Endless Night (1967).
Considering Christie is the one of the most published authors to have ever lived, on par with Shakespeare, I think she got the last laugh on that.

I don't think any of the top mystery writers took these rules seriously. And of course Doyle, Collins and Poe predate them.
I think the rules themselves are less important than the "problem" they were created to address. Classic mystery novels are a kind of game, a puzzle intended for the reader to attempt to solve, but much like a DM pitting a table of fresh level 1 PCs against a horde of CR 20+ monsters, it's absolutely within the power of the author to make their puzzle highly unfair, if not completely unsolvable, to the reader based solely on what they choose to reveal and what they choose to keep hidden - particularly for new and inexperienced mystery authors who may not have a solid grasp on the craft yet.

A mystery that hinges on the existence of a secret passage isn't a problem in and of itself, but only if that secret passage is either shown to the reader in-story or can be reasonably inferred to exist. A plot-critical secret passage that is never so much as hinted at until the big reveal at the end of the book isn't fair to the reader, in much the same way as setting up a compelling list of suspects then pinning the blame on a random, heretofore unseen burglar at the last minute is unfair. It's a rug-pull - it cheapens the experience and risks potentially turning new readers off the genre.

Whether strict adherence to Knox/Van Dine is necessary or not for a would-be mystery author, I do think striving to make your story "fair" to the reader is a laudable goal.

One of my favorite mystery stories proudly bears the tagline "No Knox. No Dine. No Fair." and centers on a witch trapping eighteen people on an isolated island in a time-loop to relive variations of a Japanese "And Then There Were None" over and over again with an ever-growing cast of witches and demons popping in to murder people in increasingly elaborate ways, all the while she and the protagonist propose/debunk theoretical solutions to the mystery by shouting colored text at one another for 100+ hours to one of the best visual novel soundtracks out there, and in spite of all of that, it nonetheless manages to be remarkably fair and completely solvable at the end of the day, so... shrugs
 
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talien

Community Supporter
I think the rules themselves are less important than the "problem" they were created to address. Classic mystery novels are a kind of game, a puzzle intended for the reader to attempt to solve, but much like a DM pitting a table of fresh level 1 PCs against a horde of CR 20+ monsters, it's absolutely within the power of the author to make their puzzle highly unfair, if not completely unsolvable, to the reader based solely on what they choose to reveal and what they choose to keep hidden - particularly for new and inexperienced mystery authors who may not have a solid grasp on the craft yet.
Yes, this.

Or to put it another way, tabletop games have a level of interactivity that makes this "fairness" more important if you want PCs to be engaged. It's can be tough to get them to even care about mundane events ("what's this NPC's name again?") much less follow the clues for a murder mystery. I'm amazed by the number of published adventures we've played that are theoretically mysteries to solve, but break so many of the above rules that PCs just wait for the next clue to pop-up and the mystery isn't much of a mystery at all.
 

Considering Christie is the one of the most published authors to have ever lived, on par with Shakespeare, I think she got the last laugh on that.


I think the rules themselves are less important than the "problem" they were created to address. Classic mystery novels are a kind of game, a puzzle intended for the reader to attempt to solve, but much like a DM pitting a table of fresh level 1 PCs against a horde of CR 20+ monsters, it's absolutely within the power of the author to make their puzzle highly unfair, if not completely unsolvable, to the reader based solely on what they choose to reveal and what they choose to keep hidden - particularly for new and inexperienced mystery authors who may not have a solid grasp on the craft yet.

A mystery that hinges on the existence of a secret passage isn't a problem in and of itself, but only if that secret passage is either shown to the reader in-story or can be reasonably inferred to exist. A plot-critical secret passage that is never so much as hinted at until the big reveal at the end of the book isn't fair to the reader, in much the same way as setting up a compelling list of suspects then pinning the blame on a random, heretofore unseen burglar at the last minute is unfair. It's a rug-pull - it cheapens the experience and risks potentially turning new readers off the genre.

Whether strict adherence to Knox/Van Dine is necessary or not for a would-be mystery author, I do think striving to make your story "fair" to the reader is a laudable goal.

One of my favorite mystery stories proudly bears the tagline "No Knox. No Dine. No Fair." and centers on a witch trapping eighteen people on an isolated island in a time-loop to relive variations of a Japanese "And Then There Were None" over and over again with an ever-growing cast of witches and demons popping in to murder people in increasingly elaborate ways, all the while she and the protagonist propose/debunk theoretical solutions to the mystery by shouting colored text at one another for 100+ hours to one of the best visual novel soundtracks out there, and in spite of all of that, it nonetheless manages to be remarkably fair and completely solvable at the end of the day, so... shrugs
I think the rules where created to address a problem that did not exist (and bash Agatha Christie). Excessive secret passages might be tiresome, as anyone who has played an early D&D module can testify, but they are not inherently unfair.

But the thing is, not every crime novel is designed to be a puzzle soluble by the reader. If it is, then fairness matters. But it doesn't matter if the killer is the narrator, or the detective, or a player character, or has special powers, or has forgotten due to a laudanum overdose, or whatever, so long as the clues that point to that are in the text. If there were novels written that were intended as a solvable puzzle, and the the clues were not there (which tends to be the problem with a D&D adventure - it's impossible to guarantee the clues will be found), then those novels have been pretty much forgotten.

But many genre novels are not intended to be puzzles that the reader can solve. Most of the Sherlock Holmes stories for example (The Hound of the Baskervilles is the exception). Frequently, Rule 1 is broken - we do not meet the perpetrator until the end. See The Sign of Four for example. This does not make them bad mysteries, and the format is a better one to aim for within D&D rules. Agatha Christie always started with the resolution and worked backwards. This is not a good model for an RPG if you want player agency. An inevitable pre-set ending is not good design.

Another model you could use in D&D is the Columbo. The players start out with a good idea who the villain is, but they need to find enough evidence to convince the authorities.
 
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