'the incongruity created when the (tragic) significance of a character's speech or actions is revealed to the audience but unknown to the character concerned; the literary device so used, orig. in Greek tragedy'Yes, I have been 'researching', 'rinos.
But what's alla that jargon got to do with anything? After all, we're not writing no Greek tragedy, no we ain't.
Well, dramatic irony is just plain awesome, when used right. If there's a bit in a book or film or TV show where you're jumping up and down and going, 'No, Bob, don't look in the wardrobe! There's a spider in there!' then you are watching a lovely bit of dramatic irony.
This is easier in film and TV, where all you need is a short scene of a spider lying in wait in a wardrobe before Bob starts to walk up to the wardrobe. But in books? In books, it's a bit harder -- when you're writing in a limited PoV, at least. How do you tell your readers something that your narrator doesn't know when you see and hear everything through your narrator, when everything is twisted by their perspective? Well, of course, you could always use the plot -- by which I mean that, for example, if a blonde girl in a horror film is walking around on her own, you know she's going to get killed whether or not you've seen the aforementioned spider (or unmentioned murderer) hiding around the next corner. However, that is one of the biggest, most boring cliches in the world.
What you need is red herrings. This use of dramatic irony is a tough line to walk across, 'rinos, but I trust you to be able to do it. What you have to do is add things in that your character won't see as important -- a handkerchief that turns out to be the solution to everything. I don't know, something like that. Of course, if that handkerchief is just thrown into the story, put in the bin, and then forgotten about by everyone, it will be too obvious, and you'll look like a fool. Have your handkerchief as a thing on a table, maybe. Have your MC use it because of the nosebleeds they're having that are realative to the story, and then tuck it into their pocket. Then have a sidekick mention the special spider-destroying cloth, and have the MC point out that they wouldn't find the thing in this dump. Make it obvious, but not enough that it screams, 'this is a book and I am giving you, the reader, a clue'.
But most of all, make it cooler than a special handkerchief.