Yes, it's the classic slasher film premise, and it was Christie who started it all. Boy, did I have my pick of which one to do for this entry! Do I go with the classic black-and-white 1945 version directed by René Clair - not only did it use the "happy ending" Christie wrote in for the stage version, it also changed character names, crimes, identities, and levels of guilt? Maybe the groovy 1965 version with Bond Girl Shirley Eaton running about in a towel in a Swiss castle? The 1974 one with Charles Aznavour performing his real-life hit "The Old-Fashioned Way" in a hotel in Iraq? Bollywood's Gumnaam?
In the end, I went with the only film to preserve Christie's text word for word. Yes, this almost meant And Then There Were None, but that version included a lot of coke and alcohol and people being haunted by the Great War and secret lesbianism and whatnot. I'm talking about the only movie to film Agatha Christie as though they had no screenplay, just the book in everyone's hands. I'm talking about...
Desyat Negrityat (1987)
dir: Stanislav Govorukhin