Nove ospiti per un delitto(1977)

"Nove Ospiti per un Delitto" is a mediocre giallo in the tradition of Agatha Christie's "And Then They Were None". Nine members of the same family go to an island, where nobody lives - but the head of the family (Arthur Kennedy) owns a nice house there. Problem is that he and his three sons keep a dark secret, and this dark secret begins to haunt them as soon as they are on the island. One by one they fall victim to a mysterious killer... (IMDb)