A brother and sister, bound by blood and forbidden desires, find themselves alone in the house. The sister, clad in a thin nightgown, can't help but notice her brother's growing bulge as he sits on the bed. He shifts uncomfortably, trying to hide his arousal, but she's already seen it. She approaches him, her heart pounding in her chest, and whispers, "Let's do something bad." He hesitates, then nods, his eyes filled with a mix of fear and excitement. They begin to touch each other, their bodies trembling with anticipation, as they cross the line into territory they've both only fantasized about.