From Crime Reads:
The word “twist” exerts a strange power over crime fiction addicts like me. Publishers know this all too well, which is why the promise of a twist is often used to advertise books that don’t have twists at all. “You’ll never see the breathtaking twist coming!” screams the press release. Well, no, you won’t, because it doesn’t exist. And so many people think a brilliant resolution is the same thing as a twist. It isn’t. Agatha Christie’s Murder on the Orient Expressoffers the most impressive puzzle solution in all of detective fiction. But, however ingenious and surprising, it’s not a twist ending.
So what is a bona fide twist? In my view, it has to be something that overturns or negates an already drawn conclusion or a firmly entrenched and reasonable assumption (Orient Express overturns an unreasonable assumption on the part of the reader, which is why I wouldn’t call it a twist).
Writing a twist isn’t an exact science, but part of what makes the brilliant ones so attractive in fiction is that feeling of having everything you thought you knew reversed, inverted or demolished; the fictional equivalent of being on a rollercoaster that suddenly turns upside down, leaving everything looking and feeling very different for the rest of the ride. And the new picture created by the shake-up of the twist has to be one that makes sense and is not risible. For example, if you find out at the end of the novel that the murderer is not the person whose fingerprints were on the knife, but rather his long-dead second cousin who developed marvelous fingerprint-forging technology unknown to science or the reader—that’s not a twist, it’s a travesty.
Link to the rest at Crime Reads
For me, the best twist is when a piece of information toward the end changes your entire perspective of the whole book. THE SIXTH SENSE is the perfect example. As to Agatha Christie, I’d say THE MURDER OF ROGER ACKROYD has that twist.
There’s a book from the “Golden Age” of detective novels, titled “Trent’s Last Case” which has the sort of twist this writer is talking about. But I can’t think of many others in any genre I’ve read.