One of the pleasures of a mystery is the contest between the reader and the sleuth as to who will solve the puzzle first. The reader wants to lose this game, but he doesn't want to find out he was duped by not being given all the information along with the detective.
The reader isn't your enemy. He's playing the game with you, so play fair. Don't purposely withhold information. Nothing puts the teeth on edge more than reading, "And suddenly, I realized what those dying words 'X' had meant." And then—silence.
The detective knows and you don't, and it's as infuriating as a playground taunt. It's just as unfair to lie by omission—to have the sleuth say nothing about something relevant she's noticed or learned. And it's unfair, to have the mystery's solution depend on esoteric information you never explain in the text.
In order to play fair and yet keep the reader mystified, borrow the tricks of another performer who hides things in plain sight: the magician. For both of us, it's a matter of distracting the eye, diverting attention. elsewhere.
One tactic is to emphasize one thing while the actual item of importance, the clue-in-waiting, is given less or incorrect emphasis. If this is done, the reader is apt to glide right over the important item and miss its significance. Consider this example:
"Wow," Gladys said. "That vase must have cost a million dollars."
I had no idea what she was looking at. I checked the mantelpiece, but it was filled with photographs—generations worth—of the Smythe family, all of whom were homely. I looked at the cluttered whatnot in the corner, but that was stuffed with Mrs. Smythe's collection of porcelain birds, mostly raptors—hawks and one Maltese falcon. Finally, I spotted the vase, and I can't imagine why it took me that long to see it—it was four feet tall and filled with peacock feathers.
If I hadn't put a Maltese falcon on that whatnot, would you have noticed it at all? It's the clue-in-waiting, but the reader would be looking for that vase, and would skim over it. Still—the reader "saw" it and the writer played fair.
A clue can be nearly anything—an action, a gesture, a speech pattern, attire—particularly if, in a subtle manner the sleuth notices (but the reader doesn't necessarily), that the item doesn't "fit" with the way the person presents himself or his history.
One good way of hiding important information is to plant it before it can be applied. Suppose we learn something about a character before he turns into a killer or a corpse. At that point, we lack a frame of reference with which to realize its significance. Only in retrospect can the dots be connected, and that's why fictional sleuths seem to have total recall, a gift few readers share.
Give the item spin. Make the fact seem to serve a different purpose than you know it does. Or have your protagonist misinterpret (at least for a while) the meaning of the clue. After all, clues are merely facts plucked out of the blizzard of sensory data that bombards us. Therefore, if the sleuth makes note of the fact, but not of its real meaning, you've played fair.
Another technique is to break your clue into several parts and scatter the pieces. In one part of the novel, we might get a fact that doesn't seem to mean much. In another, another fact that actually will relate to that first one, but doesn't seem to until later. And so on. (And of course, don't put them in their logical order. Mix them up.)
Sometimes, the clue is what isn't there or doesn't happen, e.g., Conan Doyle's dog that didn't bark in the night. Dorothy Sayers' Five Red Herrings likewise has a scene where she lists the paint tubes on the ground of a studio. What we won't register is that white isn't one of the colors catalogued, and since the painting on the easel is filled with clouds, it possibly wasn't done there, or done by that artist.
You can also hide clues in plain sight. Suppose your victim was killed by a blunt instrument which seems missing from the scene. Plunk a lot of blunt instruments within the grasp of suspects throughout the novel: ball peen hammers, a granite countertop waiting to be installed; a rolling pin (the frozen leg of lamb from the classic Roald Dahl script on Alfred Hitchcock Presents.) Show, perhaps, something that's endured a blunt instrument: a piece of hammered metal art in a workshop, or tenderized beef. (And scatter those pieces—the piece of art is in one place, given little significance, the fact that someone is an artist is in another place, the idea that that particular artist uses hammers, etc., on metal, is in another place and context.)
Add a time problem—where was that granite countertop at the time of the murders, who had that rolling pin, that ball peen hammer, when—you'll produce lots of smoke and mirrors in which to bury the real weapon, and it will feel both honest and cleverly deceptive.
Something hidden in plain sight can be an incongruous element that's given simply, then reconsidered—a sort of "wait a minute!" realization. On an early episode of Homicide: Life on the Street a blond suspect was missing, and only upon reconsideration (after we'd seen mug shots) did the detective realize that one man's eyebrows were too light. His hair had been dyed dark, but not the brows. They had their suspect.
Another trick: If you tell somebody to watch out for something, he'll seldom remember whatever preceded the watched-for item. Suppose your detective says it's important to notice who is left-handed in a group. Then you show a suspect using his left hand to write—but immediately before that happens, you put in what you want to have slip past your reader's notice.
Another distractor would be to have major action immediately after a clue's been presented. In the chaos that follows, your clue will fade in the reader's mind.
Housekeeping tip: If you're writing from more than one point of view, be careful about who knows what. It's possible that you're increasing tension by having the reader aware of something the sleuth doesn't know. That's good—but make sure the sleuth isn't basing anything on that information.
Also, it's sometimes helpful to take a printout of your manuscript and highlight clues you've planted and need to follow up on our explain. This might make it easier to be sure you've done so.
Happy sleight of hand!
Adapted from: You Can Write a Mystery, by Gillian Roberts.
© Gillian Roberts.