Pretending to Be Stepdad to Fuck Stepmom

You sneak into your step-parent's bedroom while stepmom's dozing, knowing your stepdad's not home tonight. You've had this wild idea in your mind and you finally decide to just go for it. Surely it'll never work, but it's worth a try. You quietly lift the bedsheet off and try to get into bed with step-stepmom, but she wakes up. Damn, how are you gonna explain this one? But hang on, it's pitch black and she's not even noticed it's you. She thinks you're her husband and invites you to get into bed with her! This is your chance, how far can you get this to go?