You are staying at your grandpa & grannies, but they only have one room so you are sharing with your sister. She only packed a tank top and knickers for pjamas so you are getting quite an eyeful. Perhaps that is what turns you on to begin watching porn and touching yourself in her presence. She catches you and is initially weirded out and tells you to stop,but she cant help but feel turned on hearing the porn. she begins rubbing herself and eventually asks to see your cock. She is so much into it , she feels so turned on seeing her brothers cock that she starts to show her body off and starts sucking your cock. Now you've started , you can't stop. You've unlocked something in each other as you penetrate her and she rides you in ecstasy on her brothers cock. Better not cum in her , or you two will be put into therapy for the rest of your lives!