With the movie of Curtain at last broadcast, I will now explain that Greatest Agatha Christie Clue Ever.(If you still haven't either read the book or seen the film and don't want anything given away, it's best to avoid reading any further at this point. You can always come back here later. But for those ready, here we go...)
It starts with some background.
Agatha Christie wrote Curtain in the 1940s and put it away as a legacy for her family, to be released after her death. (As it happened, though, she was imposed upon to agree to release it early, not long before her death, because of the success of the movie of Murder on the Orient Express.)
Anyway, years back upon its publication, after reading Curtain I then went back to reading other Christie novels, in no particular order, just catching up on ones that I hadn’t gotten to yet. One of those was Dead Man’s Folly (which, as it oddly turns out, they made as part of this final series of five Poirot movies, too).
One of the minor characters in Dead Man’s Folly is the mystery writer Ariadne Oliver, who Christie used on rare occasion and is very clearly her alter-ego -- among other things having a French detective who has very annoying, pretentious habits and is arrogant, and Ariadne Oliver always talks about how much she hates him.
In Dead Man’s Folly, Adriadne Oliver and some other character are talking about all this again, and she once more repeats how much she hates her detective she created…and then adds something about how she really should kill him off one day. I laughed when I read that, having recently read Curtain -- and then a thought suddenly hit me. I went back and checked the publication date of Dead Man’s Folly -- and it was in the 1950s! That means that Agatha Christie had already written Curtain and knew that she had, in fact, actually killed off Poirot. And here she was, dropping the clue to readers that she had done so!
If I’d read the books in order, I’m sure I never would have remembered that off-handed comment by the time I got to Curtain. But having read them out of order and then, by total chance, getting to it shortly after reading Curtain, that’s the only way it leaped out to me.
As I said, to me, that’s the greatest Agatha Christie clue ever. Something that she set up but didn’t pay off for over 20 years.