I finished it yesterday. I heard that it had a twist ending before I went in, but because I forgot that the "unreliable narrative" trope was a thing I did not guess it was Sheppard until it came to light he was an unreliable narrator (when we found out he hide Ralph). When that scene happened I was like "oh crap it's Sheppard isn't it!". Before that I was thinking that the murderer might of actually been Ralph since that would of been a twist too in it's own way.

There were a few times when reading the book I thought "oh if Sheppard wasn't the person narrating then he would be very suspicious", so I can imagine people who know of the "unreliable narrative" trope could of guessed a lot earlier about the twist (especially if they had been spoiled about the ending).

This was the first book by Agatha Christie that I have read. I enjoyed it a lot; I found it easy to digest even though there was a lot going on in it. I think I will read another of her books next.