If you need to hide a truth in a truth, double-meaning is your best friend. I know that doesn’t sound like it makes sense, but I promise it actually does.
A double meaning (also known as a double entendre) has a pretty accurate name – it’s when a statement or action has multiple meanings (or truths). The only part of the name that’s misleading is “double”: you don’t have to stop at 2. And you probably won’t want to – but we’ll get to that.
Now, let’s say you have a scene in a book where a character has to tell the truth, but you need that truth to serve multiple tasks. First, it needs to have an interpretation that the reader (and possibly the characters) can believe in. The sort of truth that gives them an understanding of what’s going on and what’s going to happen. Let’s call that Truth A. Truth A could easily be a plot option that you might’ve considered and decided not to go with (They’re often more predictable or obvious, but they don’t have to be.).
Then, you need that same statement or action to tell a truth that can lead to a whole different interpretation of the plot. Truth B. That truth (or possibly even Truth G) is what is really happening. By giving the reader a more obvious truth to focus on, you can keep their attention off what’s really going on – lead them astray without actually lying. Most of the time, you don’t want to straight-out lie to the readers: you simply want them to interpret the facts differently than you intend to at the end.
Think about how theologians can argue about interpretation – if this word actually means that, it changes the entire meaning! That’s the sort of opportunity you want to set up. But it’s not enough to set it up. You also have to set it up in a way that emphasizes certain truths over others.
Like a stage magician, it’s all about misdirection. In film and television, for example, they do a lot of misdirection with camera shots. The audience puts emphasis on different characters and actions by the amount of camera time they get (and the angle, focus, etc.). A great example of that is the pilot episode of Firefly. By emphasizing certain characters over others, they make you think you know who leaked the information simply because that’s how most series would have slipped you clues beforehand (Important characters get more camera time. Duh.). By breaking those rules, Joss Whedon misled the audience and surprised a lot of people who aren’t used to being surprised by tv anymore (admit it).
In writing, you can swing the interpretation the direction you want with the same basic technique of shifting the focus. Some authors even have their characters dismiss Truth A to reveal Truth B beneath – and to disguise the fact that Truth C is concealed under that. It can get very complicated, and it takes a very sneaky brain to trick someone with a truth. Luckily, we have a very sneaky language (rife with double meaning) to help us out.