A bit of a sophomore slump; the setting is highly Christie-an, and the collection of characters is nicely rounded between the horrific, the milksop and the average, but the Poirot insights often turn on very specific types of word selection that don't always seem to add up.  There's other interpretations that work just as well. The only reason Poirot can  solve it is because of the thumb of the author on the scale. You don't come out thinking Poirot is any too sharp. Mon dieu!