Writing Philosophy: Fair-Play Whodunnit

“The Butler did it!”

“B-but… that would go against Rule 5 of Ronald Knox’s 10 Commandments of Detective Fiction!”


Today’s topic:
Fair-Play Whodunnit

It’s pretty clear I’m a huge fan of Detective Fiction, and Detective Fiction tends to have many forms.

I’m a fan of all of them, be they Hardboiled (Film Noir), Great Detectives (Sherlock Holmes), Cozy Mysteries (Murder She Wrote), “Scooby Doo” Hoaxes (Obviously… Scooby Doo…).


But my most favourite of all of those forms are when they are “Fair-Play Whodunnits”.

The thing with Fair-Play Whodunnits is that it’s not a specific subgenre of Detective Fiction, it’s more of a form of writing.

The general idea is simple, that the viewer SHOULD have the same chances to figure out the mystery as the main character had THEY been in that position.

Sure, SOME stuff would be difficult to apply to EVERYONE, Hardboiled would imply they’d know how to fire a gun in the seedy underbelly of a corrupt world, Great Detectives would imply they’d have some kind of mind palace where they’re able to store all kinds of information, Cozy Mysteries… well you better have a lot of connections with gossipy old ladies and “Scooby Doo” Hoaxes would imply you would have a chase scene through a hallway with doors.

But in the end, whether something is a Fair-Play Whodunnit or not boils down to 10 particular rules. Ronald Knox’s “Ten Commandments of Detective Fiction”, also known as:

Knox’s Decalogue

  1. 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.
  2. All supernatural or preternatural agencies are ruled out as a matter of course.
  3. Not more than one secret room or passage is allowable.
  4. No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
  5. No Chinaman must figure in the story.
  6. No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
  7. The detective must not himself commit the crime.
  8. The detective must not light on any clues which are not instantly produced for the inspection of the reader.
  9. 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.
  10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.

I’ll dissect each of those rules soon.

Like the Bechdel Test however, people seem to misinterpret these rules as “if you stick to these rules blindly, your mystery is automatically good!” or worse “if you deviate from these rules, your mystery is automatically bad!”.

It IS possible to do female characters right WITHOUT beating the Bechdel Test. The same can be said for Detective Fiction.

Another thing to keep in mind is the time that these 10 Rules of Detective Fiction were written in the first place.

The rules were written in the 1920’s and it was written with the political culture in mind.

That’s why Rule 5 is there, and I will go more deeply about this later. But yeah, if we had to literally follow the rules blindly, that means any Detective Fiction that has a Chinese person in it is automatically a bad mystery, which is ridiculous.

The reason why I love a Fair-Play Whodunnit is the same reason why I love good gameplay in video games; it gives you a reason to go through the whole thing AGAIN.

I guess not so much “replayability” so much as “rewatchability”.

I like movies that encourage me to watch it again and again, that’s why I’m such a huge fan of William Shakespeare Plays, Disney Movies, Kung Fu Movies and yes of course I can’t NOT mention this; Rosencrantz and Guildenstern Are Dead.

“Will this guy ever shut up about us?” “I’m afraid not…”

But the thing with a Fair-Play Whodunnit is that it engages you to think alongside the heroes to figure out the mystery. You’re not just passively letting the movie move on in the background, you’re THINKING as you’re watching the movie.

Every scene gives you something to think about, whether it’s because they just lighted on a clue you didn’t think would be important, or because they mentioned something that you think has a bigger meaning behind it.

Thus when you rewatch the movie AFTER knowing where it will lead, it gives you more appreciation for the stuff you’ve missed.

Not to mention, if you’ve done everything right, it means the whole story is consistent lore-wise. Everything fits in together.

But yeah, let’s dissect all 10 rules and figure out what each of those rules ACTUALLY mean or encourage.

Rule 1:
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.

Now, these rules are kind of written like a contract, so to avoid confusion, let me make something clear.

“The Criminal” simply means the one behind the mystery. You’re allowed to have multiple characters who ARE criminals, but “The Criminal” mentioned in the rule set SPECIFICALLY points to the one behind the mystery the story’s about. Just because someone IS a criminal doesn’t mean they’re THE criminal.

Vincent Price, you are missed.

Either way, hope that clears things up.

The reasoning behind this rule is simple, it wouldn’t be satisfying if a suspect that enters LATE in the story to suddenly be the criminal in the end. It just doesn’t work well in a dramatic sense as you’ve barely gotten a rapport on the character before you suddenly find out they’re the villain.

Plus it feels like a bit of a cop-out if you’ve been suspecting a different character since the early part of the story only to suddenly find out it’s this newly revealed character who did it. Kinda ruins the fun.

The second part of this rule simply states that you shouldn’t be able to look into the mind of the eventual criminal, which has more to do with the fact that the criminal shouldn’t break the fourth wall and selectively edit their own thoughts to avoid spoilers.

As viewers, we’re supposed to constantly be outsiders so that we’d have an as objective (or close to the main character’s) point of view as possible, and it’s difficult to do that when we as viewers gets a peek into the mind of the villain that the main character doesn’t get to experience (which works just as much FOR us as AGAINST us, as the villain would then be able to selectively edit their thoughts to trick us as viewers).

Players of the game Heavy Rain should have some experience with that.

But, it IS possible to stick to the SPIRIT of the rule while at the same time kind of breaking it.

Say the main character breaks into the house of the suspect (who will turn out to be the criminal) and gets to read their diary. Afterward the main character finds evidence that the diary may have been planted there specifically for the main character to find. This means they’ll be able to “read” the thoughts of the suspect while at the same time giving the villain a PLAUSIBLE way to “edit” their thoughts.

Also note that it says “The criminal must be someone MENTIONED in the early part of the story”. I personally think it’s best if they actually got an APPEARANCE early on, but having the character be mentioned or have their presence felt early on works too.

The point is that the viewer can easily CLASSIFY them as a suspect as early as possible.

Rule 2:
All supernatural or preternatural agencies are ruled out as a matter of course.

On one hand I find this to be slightly elitist as I think good detective stories CAN have supernatural stuff in them.

But in general what it says is that there shouldn’t be divine intervention or have some kind of magical thing be part of the solution. I mean when you think about it, it’s kind of unfair to have a Locked Room Mystery where the whole point of the mystery is that two people got murdered in a locked room and the only clue is a sword OUTSIDE the room and then in the end it turns out the sword was simply teleported out of the room by a ghost or something.

However it really does depend on what kind of story you’re telling, really. The point of this rule is to not have unexpected stuff that don’t fit with the established rules of the current story.

A Sherlock Holmes story just wouldn’t fit with Luke Skywalker suddenly dropping in to use the Force for example.

But you CAN have supernatural or preternatural stuff in your Mystery if you simply establish them as part of the world in the first place. You kind of have to see a Mystery story as a court case where all the evidence are presented in advance for both parties to see.

Is teleportation a part of the mystery? Then give us a little arc where the limits of teleportation are explained. Can ANYONE teleport stuff? If not, then that gives you a limited amount of suspects to work with! How far CAN you teleport stuff? If not far enough for the sword to reach it’s eventual destination compared to the room, that means maybe more than teleportation was needed. Can you teleport stuff FROM a distance? If not, then you can suspect the people who were CLOSE to the locked room when the murder happened!

The big thing to think about is that there should be rules to everything. It’s by figuring OUT the rules in relation to the clues that you figure out how it all lines up.

Rule 3:
Not more than one secret room or passage is allowable.

So we’ve all known this trope where there’s a secret room somewhere where the hero will find more clues. So why is no more than one allowed? Well, the way I see it, it’s more of a “patch” rule to fix up the can of worms a secret room inherently gives to a mystery.

BECAUSE it’s such a famous trope, people LIKE having such a scene in their story, but they don’t want the can of worms opened so they patch up the rule by saying you can’t have MORE than one.

What ARE those can of worms? The fact that once you’ve found ONE secret room, your mind will kinda go all over the place and go “maybe THAT’s a secret room!” about EVERYTHING! It kinda takes you out of the mystery as you no longer look at the clues and look at the background most of the time.

Personally I think it’s best to just not bother with secret rooms altogether. The reason being that FINDING a secret room tends to be accidental which goes in conflict with Rule 6.

Rule 4:
No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.

In all honesty I kinda consider this an extension of Rule 2. Long scientific explanations tend to kill a story right in it’s tracks, but I personally think that if it’s done well in the story arc it can be kind of forgiven, the same way that magic can be forgiven.

That said, though, I’d advice not doing too many of those things one after another. You still have to think about the engagement of the viewers and it’s kind of difficult to do that if they pretty much have to have an essay in their mind on how everything works to figure out the mystery.

At the very least simplify the poison or magic to have one simple effect with MAYBE a side-effect. And if you’re gonna do that, just use a well-known poison and be done with it.

Rule 5:
No Chinaman must figure in the story.

So yeah, there’s something of a political thing with this rule. You see, these rules were written during the Chinese Exclusion Act which ran from 1882 to 1943. The American People in power kinda chased out Chinese Americans and Chinese people in general were antagonized, characterized as a lazy, opium-addicted menacing horde called the “Yellow Peril” (ignoring that Americans GOT Chinese people addicted to Opium in the first place…).

Of course the people in power immediately sucked UP to the Asian people during the Cold War when they needed their help, creating the positive discrimination that Asian People are SO SMART!

Funnily enough it was made to talk DOWN to the African Americans by stereotyping them as uncultured and dumb, so it’s not like Asian Americans were exactly PROUD of the image. Yeah, now you know the history of THAT…

Either way, the point is that during the writing of these rules, Chinese people were generally frowned upon from the start, meaning that when you watch a movie during the time of the Chinese Exclusion Act, the viewer will inherently be biased AGAINST the “Chinaman”, whether they deserve it or not. It colours the objectiveness of it, which would kill the Fair-Play Whodunnit angle.

Nowadays there’s no reason NOT to include a Chinese character or even Asian Characters as a whole as there’s generally no negative or positive bias against them.

But knowing the world, there’s ALWAYS going to be a group of people for whom there will be cultural bias against, and that’s what “The Chinaman” in this rule pretty much means.

Personally I would prefer if I could just ignore this rule altogether, but the truth of the matter is that cultural biases will ALWAYS be a thing and there’s no way to control it, so the best way to handle this is to just figure out in advance what WOULD be the current “Chinaman” so to speak and just avoid putting them in the story altogether to keep the mystery from being buried by controversy over it’s actual… you know… mystery.

By the way, this rule is ALSO the reason why Butlers, Maids or servants in general aren’t allowed to be the criminal either, because it’s been done SO MUCH TO DEATH (EVEN IN THE TIMES THIS WAS WRITTEN MIND YOU!) that butlers are already inherent suspects.

That said I wouldn’t mind the appearance of a Butler, Maid or Servant as long as they IMMEDIATELY get cleared out of being suspects from the get-go.

Rule 6:
No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.

This rule is mainly the reason why MOST Sherlock Holmes stories AREN’T Fair-Play Whodunnits. When you have a detective who’s SO smart and SO clever that he can come to conclusions that no earthly being can follow, then it’s kind of impossible to posit that any viewer in his position could have solved the murder themselves.

That’s kind of the difficulty with Fair-Play Whodunnits, the fact that you have to distance from the Escapist Fiction where the main character is a badass you look up to like Sherlock Holmes or Batman. Instead the best Fair-Play Whodunnits work when the detective is ABOUT as smart as the viewer themselves (or at least the target audience).

Accidents kind of work in the same way, as a fortunate accident would not be based on the skill of the detective but instead it’s just something that the plot demands. This is kind of a mirror of the previous thing where instead of the detective being SMARTER than the viewer, here he’s just LUCKIER than the viewer.

Mind you I’m personally a bit more lenient on the second one, because in the end I think the main point of this rule is that there should be INTENT on finding the clues to solve the mysteries.

There should be a cause and effect where the detective finds Clue A and as a result does an action to find Clue B.

Say if a detective thinks someone walked AWAY from somewhere, so he looks for footprints, which is why he looks around a muddy area. Then it turns out that walking INTO the muddy area he doesn’t find footprints but instead finds a cut off cable.

Did he “accidentally” find a clue he wasn’t looking for? Yeah, kinda, but on the other hand it was his own action and deduction that LED him to that clue to begin with.

Rule 7:
The detective must not himself commit the crime.

Similar to “The Criminal”, “The Detective” particularly means the character (usually the protagonist) who’s actively seeking to solve the mystery.

It is possible to have characters who ARE detectives in your whodunnit, and it is also possible for “The Detective” to NOT be a detective. For example, Miss Marple is “The Detective” even though she’s not officially a detective. By contrast Inspector Lestrade of Sherlock Holmes IS a detective, but he’s not THE Detective. So you ARE allowed to have A detective be the one who committed the crime so long as “THE Detective” was not the one who did it.

This is kind of a mixture of Rule 1 and Rule 5, so I’ll keep this short. The detective inherently is a character you trust because you get to hear their thoughts. If they WERE the criminal in the end, that would be okay in a THRILLER (or comedy like in Clue), but NOT in a Fair-Play Whodunnit, because that means they’ve been manipulating your ability to have an objective view of the mystery.

In Death Note’s case, though, we knew from the start that Light is Kira and it’s a thriller about whether he’ll be caught or not.

Again, it’s acceptable if there were TWO detectives, of which the detective that committed the crime would be something like the Rival or Mentor or whatever whom you’re unable to truly read their minds while THE Detective keeps being the one who’s SOLVING the crime rather than COMMITING the crime.

But to keep it safe, just don’t make the detectives themselves the criminal when it comes to a Fair-Play Whodunnit.

Keep it in thrillers where it’s about shock rather than deduction.

Rule 8:
The detective must not light on any clues which are not instantly produced for the inspection of the reader.

It’s worded in a bit of a double negative here, but the point of the matter is that when there IS a clue, the detective (or in a movie the director themselves) should highlight it AS a clue.

Like I said earlier a Fair-Play Whodunnit is like a court case where all the evidence/clues are put on the table so everyone can make a narrative out of it.

It would thus be unfair if the detective noticed something while the viewer didn’t. That’s not how it works in a court case either, both sides are aware of all evidence (don’t believe what Phoenix Wright does all the time).

Of course, in a movie it would be pretty annoying if a detective would constantly point to every clue and say “Hey! This is a clue! It’s a clue because X and Y! I will now put this clue in the clue folder!”. That’s where the directing comes into play. You can instead highlight the detective noticing something with a zoom in of the clue, close-up of the detective thinking about it or maybe have them note it down.

Movies are a visual medium after all. It’s actually kind of an advantage the medium has when it comes to representing Detective Fiction, seeing how in books every single event that happens is pretty much in the text itself.

Rule 9:
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.

Now personally I find it a bit unfair to call Watson the “stupid friend” as he’s more like the straight man to Sherlock Holmes who is a genius, but it IS a trope for a mystery for the detective to have a friend/ally/colleague who isn’t AS smart as the detective.

This rule is also kind of an extension of Rule 7, the so-called “stupid friend” would generally be someone that the viewer would be able to hear their thoughts about. They are usually the audience surrogate after all, constantly asking the questions to get more of an understanding of the world.

Bottom-line is that AS an audience surrogate, they shouldn’t hide anything from the viewers. As viewers we’re supposed to be able to put ourselves in their position and figure out the mystery FROM that position, and it’s difficult to do that if there’s a plot twist that they knew something we don’t.

Rule 10:
Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.

And finally we end… with an extension of Rule 2 and Rule 4. Yeah you know this cliché, “it wasn’t ME! IT WAS MY EVIL TWIN!”. But as it’s noted in the rule itself; “unless we have been duly prepared for them”.

That’s pretty much what I said about Rule 2 and 4, in the end it’s okay if enough time was given to the viewer to plausibly take all of these information into account.

Sure, it may spoil the “SHOCKING TWIST” that there’s an evil twin if literally in the early part of the story it’s mentioned “Oh yeah, I have a twin brother… I don’t like him…”, but again that’s what a thriller is for.

A Fair-Play Whodunnit is NOT about shocking plot twists, it’s about being able to figure out everything alongside the detective. And twins or doubles are just so easy of a cop-out solution that unless you’ve prepared the audience for it in advance (and it’s VERY hard NOT to do it clumsily) it’s gonna be just that… a cop-out.

The Summation

So yeah, that’s my dissection of the 10 Rules of Detective Fiction.
I would like to note that the quality of a mystery does NOT rely on whether it’s a Fair-Play Whodunnit or not. In the end there are many different ways a mystery can be engaging.

Most Film Noir movies are generally about the exciting chase towards the truth like the Maltese Falcon over actual clues.

Great Detective movies are generally about presenting the detective as a genius over actually being fair.

“Scooby Doo” Hoaxes are generally about funny hijinks while just occasionally delving into the clues.

Heck I think Cozy Mysteries are the only subgenre of Mysteries where you can pretty confidently say that they’re most LIKELY Fair-Play Whodunnits, since it doesn’t tend to engage people through chases, the genius of the hero or funny hijinks.

That said, it is possible to make a Fair-Play Whodunnit out of all Mystery Subgenres.

And I just have my reasons to love Fair-Play Whodunnits. Most likely it’s because I grew up with video games where replay value is key, and thus I kind of put that importance in movies too.

Published by Huy Minh Le

Huy Minh Le is a Video Game Enthusiast, Movie Lover, Writer, Content Marketeer and regular TvTropes reader! His studies in Game Design, Art, and Writing has led to a very creative, yet analytical mind.

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