Stumbling upon my stepsister Kath's late-night porn habit, I find her flushed and breathless, her hand buried in her panties. Her eyes meet mine, wide with surprise, but I see the hunger there. I lock the door, joining her on the bed. 'Let me help,' I whisper, my hand replacing hers on her wet pussy. She gasps, her hips bucking as I finger her, my thumb circling her clit. Her moans fill the room as I bring her to a shuddering orgasm, her pussy clenching around my digits.