Your step-sister's secret smile hints at a shared naughtiness. She leads you to the pool's edge, her bikini bottoms already discarded. She shows you her vibrator, its sleek surface glinting in the sunlight. "Shh," she warns, as she turns it on, low and steady. She closes her eyes, her hips moving in tiny circles, her breath coming in short gasps. You watch, your own breath ragged, as she brings herself to the brink, her pussy swelling and pulsing. She reaches for you, guiding your hand to her clit, and you rub in time with her vibrator, feeling her tense and quiver as she comes, her orgasm silent but intense.