You cannot find many movies of this genre that are worth seeing, usually because either the screenplay isn't that good or the actors performance is bad.luckily, in this movie everything works like a clock.Peter Ustinov gives us another great performance as he did in "EVIL UNDER THE SUN".The rest of the cast are not bad but some could have been a little bit better. The screenplay is very good but sometimes it loses control and the movie becomes a little bit boring, especially at the beginning, until the first death. To sum up, this is a movie that you see only once{knowing the plot ruins the whole movie that's why i'm not telling you it}, but is a thriller that everyone should see. I give it 10/10.