I've just finished reading a book and briefly I was upset. I felt manipulated by the author - cheated. At first sight, this is a pretty feeble reaction. The whole business of writing fiction is a matter of manipulation. To transfer the reader from their comfy chair to a different place, into danger, into someone else's head - it's all manipulation. But the good author does this in such a way that you don't notice. You mustn't ever see them pulling the strings.
Now in this case it was puzzling that I felt like this, because it's a very good author indeed. So what was happening? I won't tell you who, or which book, or this will turn into a spoiler. But it was a crime novel. When I'd bought it, Amazon had splashed after its name 'an X Y crime novel', where X Y is the name of the writer's detective. Yet by the time I got 3/4 way through the book it was very obvious that X Y only had a bit part - another detective was the main character.
Here's where the strings become visible. If you say it's an X Y crime novel, but the main character is a colleague of X Y's then it's almost inevitable that main character is going to be killed. Otherwise, why isn't it an A B crime novel instead? And sure enough, she was. My immediate response was irritation. I had been manipulated into getting into the head of A B, so I would be more shocked when she died.
Yet after some thought, I realized it's not the author's fault. Taken as a standalone book, this is a very effective plot device. And it was brilliantly handled - I literally had a tear in my at A B's funeral scene. It's only because I was expecting an X Y crime novel - because Amazon told me that's what it was - that I felt manipulated.
I think there's a lesson in there somewhere about the difference between an exciting plot twist and something that irritates the reader. Not in the plot but in the way just that simple sentence 'an X Y crime novel' could so alter expectations.