On my very first reading of Prisoner of Azkaban, I never guessed that Professor Lupin was a werewolf. (GOSH, DID I GIVE IT AWAY?) Later, I would wonder how I didn't put more thought into the silvery-white orb that was Lupin's Boggart. Not that I would necessarily have guessed anything, but why didn't I think more about it?
Why? Because Rowling DELIBERATELY AND BRILLIANTLY THREW ME OFF. I'd forgotten one line, right after the scene wherein Lupin's Boggart appears: "'I wonder why Professor Lupin's frightened of crystal balls?' said Lavender thoughtfully."
When writing a story with an element of mystery, or one that's supposed to have a surprising twist, it can be helpful to employ what I suppose is just a special kind of red herring: making your characters work from flawed assumptions. Basically, if you leave something totally open - e.g. having Harry and friends wonder what that silvery-white orb could possibly be - then readers may solve the mystery before you want them to. If, on the other hand, you provide a plausible conclusion to which your characters can jump, then readers are less likely to poke around the clues too much and figure things out.
There are, of course, some caveats. Which means it is LIST TIME!
- Don't feel like you have to clarify that there are other possibilities. (Imagine Hermione saying, "Crystal balls? Are you sure that's what that was? Couldn't it have been something else?") The strength of this technique comes from the fact that it can prevent readers from thinking there are other possibilities. This can be hard, because you don't want readers to think your characters are blinded or stupid. They won't, though, if you . . .
- Make sure the assumption is plausible. This is key. It should seem perfectly natural for the characters to assume this - so natural that the reader assumes it, too, and spends her/his time wondering about other things. Of course, it helps if you . . .
- Downplay the whole thing. You don't have to do this, but if your characters have a lot of conversations, plans, etc. based explicitly around their flawed assumption, readers may spot a possible alternative and become frustrated with the characters for not checking their facts when something important is at stake. If, on the other hand, you have characters just shrug something off with a wrong guess - no one besides Lavender ever mentions anything about Lupin being afraid of crystal balls - then the reader is likely not to think too much about it, either.
Mysteries and surprise twists are hard, because it's difficult to know how much the average reader will have figured out at any point and what s/he will suspect or expect. Naturally, even if you have your average reader pegged pretty well, there will always be those freakish people who guess right based solely on reading Lupin's name before he even wakes up on the train. Then, too, you'll have people who don't get it even after the characters finally do. I haven't written a lot of mysteriousness, and suspect it gets easier with practice to guess what people will be thinking as they read. It also helps, as with other aspects of editing, to set the story aside for awhile and get fresher eyes.
In highly related news, I'm not too far from the end of this edit of The Dogwatchers! Soon, I will be ready to find out how successful the mystery/surprise elements are for some of my wonderful reader-friends!