Fan Casting Clue (AutobotSonicFan's version)

Mike Green and four other strangers are invited to millionaire Boddy Black's mansion. But he and his maid Mrs. White were mysteriously murdered, and nobody knows where it happened (because the killer messed up every room in the mansion to cover their tracks), how they killed them, or obviously who it is. Nobody else but six other people were inside. It could be Green. Or it could be the Oxford professor Peter L. Plum. Or Cold War veteran Col. Angus Mustard. Or the seductive and alluringly-beautiful Scarlett. Or the bird-watching Ava Peacock. Or even White's adoptive daughter Lillian Orchid. It could be any one of them. But who? With what? And where?