The house is quiet, save for the muffled sounds of their parents' lovemaking next door. Step-sister and brother, left alone with their hormones and curiosity, find themselves drawn to the keyhole. He's hard, she's wet, and neither can look away. They watch, entranced, as their father's muscular body moves over their mother's lithe form. His hands grip her hips, pulling her onto him, making her gasp. The sister's hand finds her brother's, guiding it under her skirt, encouraging him to touch her, to feel how turned on she is. They're not just watching; they're participating, in their own forbidden way.