Triangle of Venus (1978)

Sun-soaked Seychelles: As a professional tennis player, Michael once had some success and made some money. As success went downhill, he began to gamble and lost all. On the last game he plays on his wife Julia and loses her to Howard, a casino owner and slave dealer. She goes with him happily and without hesitation and asks for a divorce. Her best friend Sylvia is Michael's mistress and she is happy with the situation. She persuades Michael to murder his rich aunt Lady Henriette for her millions. He is actually her illegitimate son, but he doesn't know this. Lady Henriette is killed by her servant, but her young private investigator Peggy gets involved and warns Michael about his mistress' and wife's plot to kill him.