Your reserved sister in law finds herself unusually and ridiculously horny right before you show up. She starts to grope her own tits and starts rubbing her pussy like never before. She never masturbates, she thinks it’s a dirty act. You walk in on her just as she’s starting to cum, but she can’t stop. All she can do is look at you in horror as she keeps furiously rubbing herself and cumming right there in front of you. She sees you’re starting to get aroused and she wants your cock, surprised at herself and embarrassed she seduces you into fucking her and knocking her up. She knows it’s wrong, she can’t have her brother in laws seed in her but she can’t stop.