In a cramped, dimly lit bathroom, a brother and sister find themselves alone, their shared secret evident in the bulge in his pants and the flush on her cheeks. She leans back against the cool tiles, her eyes meeting his as she slowly pulls her shirt over her head, revealing her lacy bra. He swallows hard, his Adam's apple bobbing, before stepping closer, his hands finding her hips as he pulls her against him, their bodies fitting together like two pieces of a puzzle.