At our last literary coffee klatsch someone mentioned reading [b:Murder on the Orient Express|7269156|Murder on the Orient Express|François Rivière|https://images.gr-assets.com/books/1330556949s/7269156.jpg|19052226], and that led to a discussion of books about people in confined spaces. Our local library didn't have a copy of that, so I took this one out thinking that a boat, like a train, is a confined space. In a crime novel it limits the number of possible suspects.

Colonel Race, looking for a spy, teams up with Hercule Poirot to discover who murdered a wealthy tourist on a Nile steamer. After they have interviewed the main possible suspects Colonel Race made a list of "what we know so far", and it was at that point that I worked out whodunit, but not quite how it was done.

The bigger puzzle, for the first half of the book, was not trying to finger the perpetrator, but trying to work out who the victim would be.