Guy Hamilton does wonders here with this fairly far-fetched Agatha Christie story about the murder of an actress - a rather unlikeable creation of Diana Rigg - on an idyllic if somewhat ramshackle island paradise run by Maggie Smith. Peter Ustinov is on hand, luckily, to exercise his little grey cells and establish who did what to whom, and why! James Mason, Sylvia Miles and Roddy McDowall head the supporting list of suspects as "Monsieur Poirot" tries to suss it all out. It is quite an enjoyable affair with some attractive scenery and a few fun sub-plots to the main theme, but it doesn't…