I went on an Agatha Christie binge a number of years ago until I realized that in most cases I was able to figure out who did it in the first couple of pages. I’m sure she didn’t do this in all of her stories, but quite often:
A character – whether major or minor – is introduced at the very beginning of the story and immediately given an airtight alibi as to why he or she couldn’t possibly be the killer. At the end of the book, you discover that the person’s alibi isn’t really as airtight as we were led to believe, and he or she is, in fact, the killer.
Regards,
Barry