Blackmail with sister incest plus slut

In this type of situation you can find yourself if you do what you should not. The man had sneaked into the room of the slutty sister-in-law, his wife's sister, to smell her underwear. That makes him horny and helps him think about something sexual when he fucks his wife. But while the sister-in-law is doing it, he catches her and tells her that now she is going to have to fuck her if she wants him not to say anything to her sister. He reluctantly accepts, but in reality he is delighted to be able to get his wife's sister's slut's cock.