Books forgotten, the siblings' minds wander to forbidden desires. She suggests, 'A different kind of lesson?' They move to her room, her heart pounding as she feels his gaze on her body. He runs a finger along her spine, making her shiver. She bends over, offering herself to him. He takes her, slowly at first, then harder, their bodies meeting with each thrust. She gasps, feeling him fill her, their pleasure mounting until they climax together, their moans muffled by the closed door. They part, quietly, returning to their homework, their secret etched into the afternoon's silence.