I just started college and moved in with Mandy, my older sister, and Tom, her husband. They live closer to the school than my parents. Mandy thinks I don't know that she knows I'm now fucking Tom. She knows. I just want to work it into a threesome before discussing it. Mandy and I used to mess around a bit and talk about watching each other get fucked by some guy when we were kids. Now's our chance.