Under the guise of studying together, a sister and brother find themselves alone in the living room, their bodies inches apart on the couch. The room grows warmer, their breaths shallow. She looks at him, her eyes filled with a mix of fear and desire. He notices, his own heart pounding in his chest. She licks her lips, then reaches out, her hand resting on his thigh. He sucks in a breath as she inches closer, her fingers creeping towards his growing erection. He captures her wrist, their eyes locked. "We shouldn't," he whispers, but his body betrays him, his cock hardening at her touch. She smiles, a wicked glint in her eye, and leans in, ready to cross the line.