This is the sort of book that Agatha Christie absolutely excels at. It's starting point is an absolutely over-the-top murder method designed to be perfect, and it combines a popular-at-the-time hint of the supernatural. What's great about this book is that at several points the reader has absolutely no idea how she is going to pull it all together and come up with a rational solution. And then she does, of course, because she is simply the best plotter in the mystery canon.
So who's in it? It doesn't matter, of course. Some young attractive people, a wily Inspector, and Ariadne Oliver, the mystery writer who shows up in a few of Christie's books. The Pale Horse is an old pub, now inhabited by three witch-like ladies. Local rumor has it that they can kill from a distance. A lot of fun, and I'm sure it would make a terrible movie.