I read this one for the "overseas travel" square because it gets Miss Marple out of St. Mary's Mead on a long vacation to the sunny climes of the West Indies. As is often the case with Christie, the reader must, rather uncomfortably, wade through some casual racism/colonialism/sexism to enjoy the mystery.
I don't think that this is one of Christie's best, though. Her mysteries often rely strongly on coincidence, but this one takes the use of coincidence to a whole new level of ridiculously unbelievable. I did enjoy the introduction to Mr. Rafiel, and would've liked to hear more about him. He made a nice counterpoint to Miss Marple.