In the dimly lit room, the boy lies back, his fingers dancing over his naked body, teasing his nipples and tracing the lines of his abs before wrapping around his throbbing length. His eyes are closed, lost in his own world of fantasy, until a creaking floorboard snaps him back to reality. His sister stands in the doorway, her eyes wide with surprise and something else - curiosity perhaps, or maybe even desire. The boy freezes, his hand still gripping his cock, as his sister steps closer, her gaze locked onto his most intimate moment.