"EVIL UNDER THE SUN" (1982), from the first time I saw it on HBO (I never even heard of it until then-- I suspect it didn't even run in my area at all, or if it did, that it vanished after 7 days) , has long been a close 2nd for me after DEATH ON THE NILE as my favorite AC or Poirot film. Unlike "...NILE", though, I had a much harder time remembering the details. I loved the locations, the cast, the dialogue, the music... but it seemed to me they picked that particular story to do because it was the most complex mystery they could find. At the end, it would always make sense, but I could never follow the details or logic of it.
Then, a few years ago, I almost fell asleep on the end. After, I got so annoyed, I went to get a snack, came back, re-ran the tape to exactly where Maggie Smith says, "You mean-- NOBODY did it!" and Poriot replied, "And yet... we STILL have... a body." --and watched the end again.
AND SUDDENLY, after more than 20 years, the WHOLE DAMN FILM made sense to me!!!!
I've seen it multiple times since, and unlike before, each time now, I KNOW exactly what's going on. And why. The why is important. And they don't really stress that in the film itself. But trust me, if you don't understand the motives, the actions are almost impossible to keep track of!!
I think "EVIL..." may have surpassed "...NILE" in my eyes these days. I just love it.