More evil under the sun
This isn't one of Christie's greatest mysteries, but it's well constructed, and has a great new character in the eccentric and exceedingly grumpy millionaire, Jason Rafiel (who would feature, from beyond the grave, in the creepy Nemesis).
Written in 1964 it marked a definite return to form for the crime writer. Oddly some elements in the crime are closely related to the much earlier Sleeping murder (although published posthumously, it was written during the Second World War) with Christie's regular themes of murder and induced madness important here.
Caribbean mystery has also been immensely helpful to me in enabling me to tick off another country for my 666 Challenge. Sadly, it doesn't look as though I'm quite going to be able to complete the challenge this year, but there should be just a few countries to go to finish off the challenge in the New Year. The Christie thriller is set on the fictional West Indies island of St. Honore, but Christie had been inspired to set a mystery in the Caribbean following a holiday there in the company of some archaeologist friends. St. Honore is reputedly the real life island of St. Lucia, part of the Lesser Antilles, so it's another one to tick off my North American list.