As the clock strikes midnight, the siblings creep into each other's rooms, hearts pounding with anticipation. She, clad in a silky nightgown, sits on his lap, feeling his growing erection through his pajamas. He, his hands trembling, lifts her gown to reveal her bare, ready sex. They grind against each other, their bodies slick with sweat, until they both climax, their moans muffled in the night, their secret safe, their desire insatiable.