Death on the Nile, by Agatha Christie, 1937.
I love Agatha Christie's writing, but this is not one of my favorite mysteries. For one thing, I missed Captain Hastings. Poirot has remarked in several mysteries how much he needs Captain Hastings because he can think like an "ordinary man". That may be true, but he also needs him because Hastings will mock him and will stand up to him. Of course, Poirot will solve the mystery and look terribly clever, but it is fun to laugh in a kind and loving way right along with Hastings.
There is much of "the psychology" in this book, possibly too much. The mystery itself is not too difficult to work out, it is the how that is complex, but there is so much muddying of the Nile waters in this story. And, even though I am told to like Mrs. Allington, Rosalie and Cornelia, I just didn't find them as engaging as some characters in other Christie books.