And Then There Were 38: Evil Under the Sun by Agatha Christie

While this one is something of a fan favorite, we were surprised by
the simplicity of the central mystery upon a reread, given all the
Christie puzzles we've solved thus far.... Add to that a number of
characters who are never really suspects, plus a few absurd
side-plots that don't quite hang onto the main action as they
should, and we come out a bit more critically on this one than we
expected, despite retaining a healthy affection for some of this
Poirot novel's better elements.