Curiosity piqued, a sister and brother find themselves alone, their hormones raging. She retreats to the bathroom, fingers exploring her slick folds, moans echoing off the cold tile. He stumbles in, catching her mid-act, his own body betraying him with a growing erection. They clash, words sharp, but later, they retreat to her room, naked, aroused. She watches, enraptured, as he strokes his thick length. Their mutual desire palpable, they inch closer, but a sudden knock at the door forces them to freeze, their forbidden game interrupted.