There’s a certain amount of artifice to crafting a mystery in a story. Okay, the whole process of crafting a mystery is basically artifice, but let’s set that aside for a second.
The most important resource to balance is information. How much to give the reader, when to give it, and how to provide it. These are probably the most important decisions that affect the plot of any given mystery. When are the characters provided a vital clue? When does that clue become available to the reader? It varies from writer to writer. For some, the reader is never provided with all the puzzle pieces, leaving them in the dark until the story’s Great Detective pieces them all together from an armchair or a drawing-room. For others, the reader is given each clue, every step of the way, and if they’re quick on their feet, they can beat the characters to the solution.
But something I feel like writers should never do in the context of a mystery is lie to the reader. Omissions are fine. Half-truths are occasionally acceptable. Misinterpretations of evidence as reinforced by earnest characters are always permitted. But writers should not lie to the reader over the course of a mystery story. This is why you will rarely, if ever, see an unreliable narrator at the heart of such a story.
As proof of my thesis, I present two scenarios. Brace yourselves for spoilers for BBC’s Sherlock and Gainax’s Neon Genesis Evangelion.
At the conclusion of the second series of Sherlock, our titular high-functioning sociopath apparently plummeted to his death from the top of St. Bart’s Hospital. His death was confirmed by his compatriot John, who had been conveniently clocked in the head shortly after the evidently fatal jump. It is swiftly revealed that Sherlock did not, in fact, perish, and fans of the series were left to writhe in agony for a positively intolerable quantity of time while trying to figure out how Sherlock managed to fool goddamn near everybody.
In the third series, Sherlock provides Anderson (formerly of Scotland Yard, now professional wacko-cuckoopants) a bizarre and weirdly ungainly explanation for his faked suicide and obvious survival.
During this conversation, it should be noted that Anderson is effectively acting as an audience surrogate, and Sherlock is more or less a mouthpiece for Steven Moffat and Mark Gatiss, the show’s creators.
At the conclusion of Sherlock’s explanation, which seems wildly improbable, given the number of people who were required and the fact that they all somehow managed to keep their mouths shut about helping fake a suicide, Anderson doesn’t buy it. As a consequence, neither does the audience.
But neither the audience nor Anderson gets any more out of Sherlock. As baffled Anderson-viewers, we have been offered utter horseshit by an insufferably smug Sherlock-as-Moffat-and-Gatiss with no recourse. Understandably, this made a lot of people extraordinarily unhappy. If I’m honest, I’m still fairly irritated that there was never a straight explanation given for Sherlock’s survival.
This is what happens when you lie to your audience. They get pissed. Moffat and Gatiss deserve a smack on the wrist for that one, at a minimum. It was calculated, it was deliberate, and it was a dick move, bro.
Contrast this, however, with a scene from the later half of the run of Neon Genesis Evangelion. One of the characters, a man with an incredibly mercurial sense of allegiance named Ryoji Kaji, is caught trying to infiltrate a top-secret area called Terminal Dogma. It’s just his luck that Katsuragi Misato, his off-and-on lover who is ranking military, is the one who caught him.
She descends into Terminal Dogma with Kaji, however. There, in Terminal Dogma, Kaji introduces Misato to Adam: the first of a series of horrific monsters called Angels.
There’s only one problem: Kaji is dead wrong. The creature in Terminal Dogma is not Adam. It is, in fact, Lilith, the second Angel.
So now we have two situations where a character has uttered an untruth: Sherlock’s explanation of his faked suicide, and Kaji’s identification of Lilith as Adam.
What makes Kaji’s false assertion okay with the audience—and by extension, an acceptable move on the writer’s part—is that the audience is aware that Ryoji Kaji is working with the intel he has on hand. He’s as blind as the audience is, trying to piece together the machinations of madmen using scraps of data and his wits. With what he’s cobbled together, the best hypothesis he can formulate is that the creature in Terminal Dogma is Adam. It’s just unfortunate that his best hypothesis is incorrect.
Kaji also has the added advantage of not being a mouthpiece for Anno Hideaki, the show’s writer.
So there you have it. My thesis: your characters (so long as they are not the reader’s only POV and so long as they are not author stand-ins) can fuck up, make bad guesses, prevaricate, or outright lie all they want. That is acceptable to the audience. But what is never okay is for you, as a writer, to deliberately, directly feed your audience bad information.
That’s a real fast way to chase readers off. And a lot of the time, they sure as hell won’t be coming back.