On a packed metro ride, a brother and sister, strangers to each other, find themselves pressed together in the crowded car. Their bodies brush, eyes meet, and a spark ignites. She's wearing a short skirt, he's sweaty from work. They exchange no words, but the tension is palpable. As the train lurches, she accidentally-on-purpose grinds against his growing bulge. He responds, his hand sliding up her thigh, teasing the edge of her panties. The journey is long, the stops frequent, but their connection intensifies, culminating in a secret, thrilling, public encounter.