Unlike Books 2 and 3, where I somehow (disappointingly) managed to figure out the cases fairly early on, in this one I merely identified the murderer based on a short description of his eating habit, but not the motive.
So now my opinion of the series has changed completely. I love the characters and the settings; but the quality of the mysteries are somewhat lacking. I might be a mystery fan, but I shouldn't be able to guess 3 out of 4 of a series' whodunits. The enjoyment comes from the suspense of being completely surprised by the ending.
Having said that, I think this one was my favorite of the series. The tropical location, the classic Agatha Christie-esque crime in a big house with a dwindling number of suspects ... even if it ended on a sad note (the looming Second World War), it was still good fun to read.