Nothing affects you quite like a truly great twist ending. Famous examples include Shutter Island, Fight Club and Agatha Christie's And Then There Were None. But nothing is quite as infuriating as a twist ending done badly. You're the author, so the ending isn't supposed to surprise you...so how do you know when your ending is a surprise to someone else?
Twist endings, by definition, completely change the plot of the story. They come as a surprise. Something unexpected happens, and everything is different. This can be done for dramatic or comedic effect...and it can be done poorly either way, too.
Bad twist endings can appear pretty much anywhere, and you can blame all sorts of culprits. It's much easier to learn how to recognize the elements that make a twist ending good, because lots of stuff can make it bad.
- Logic. Good twist endings don't ignore logic. If I read your book for 300 pages and I'm trying to figure out whether the girl and the guy will end up together or if the mean ex-girlfriend and stepmother will be successful in their plot to unhinge the romance and all of a sudden a serial killer with a chainsaw comes along and kills everyone and there's been no previous reference to a chainsaw killer in the book...well, I'm not going to write you a very nice review. Crazy serial killer is a twist ending, but when it's totally random it is not a good one.
- Reveal. A really juicy twist ending often reveals some new piece of information about a character that was kept secret for the whole of the book (until now). Revealing that the main character is actually a woman disguised as a man and she's the one who was having the affair with Steve -- not Carol, who was killed for the aforementioned affair in Chapter 2 -- is an example of this technique.
- New development. The new development is a classic type of twist ending. A letter arrives in the mail, a rich relative dies, someone gets killed -- some brand-new plot happens that completely changes someone's circumstances. This is a tricky method, because you have to maintain the logic. The relative must be mentioned in the book, the victim must be introduced early...it has to make sense.
- Really? It's hard to do this, but shock and awe can also be used as a twist ending. Unexpectedly killing the main character (or several characters) will leave readers with their mouths hanging open. A catastrophic event is certainly a memorable ending, but make sure it brings some resolution. You have to provide satisfaction when you dole out chaos.
After you write your twist ending, run it through a couple of beta readers to see how they feel about it. Read it yourself, and check for the elements that make endings good. A well-done twist ending will leave readers feeling something about your book, and that's a good way to leave them.