Barging into the bathroom, I found my stepsister, a leggy teen in stockings, feverishly rubbing her wet pussy under the covers. She thought she was alone, but I'd caught her. Her eyes widened in shock, but I couldn't look away from her big ass bouncing as she fingered herself. She begged me to leave, but I was transfixed, my cock hard at the sight of her. When she finally noticed my bulge, she hesitated, then smiled, pushing her hips forward, inviting me to watch her finish.