In the Folds of the Flesh (1970)

Pascal Gorriot, an escaped criminal, accidentally witnesses Lucille disposing of her second husband Andre's body at sea. Thirteen years later, Andre's cousin turns up at Lucille's villa with his Alastian dog. It's not long before creepy Colin, Andre's son, strangles the unfortunate hound and Falaise, Andre's daughter, stabs their unwelcome family member to death. Another unwanted visitor friend arrives and rapidly seduces Falais. Colin is jealous and warns the Don Juan about the dangers of being a male praying mantis and it's not long before Falaise decapitates him. Pascal, the ex-convict who witnessed the murder of Andre is the next intruder. He takes the family hostage and demands blackmail money, prompting them to do away with him in an acid bath. The police investigate and a chain of deception and murder is revealed...