The house echoes with emptiness as she leaves them once again. The boy, alone and horny, strips down to his socks, his cock throbbing with anticipation. He strokes himself, the sound of his hand moving up and down his shaft filling the silent room. His other hand plays with his balls, fondling them gently. He pictures her, his sister, her curves, her smile, her moans. His breathing quickens, his strokes become more urgent. He can feel his orgasm building, his cock swelling. With a final, desperate stroke, he comes, his cum shooting out, coating his hand, his belly, and his socks.