Checkbook presents a taboo tale of sisterly desire. She was always the 'good girl', claimed to be celibate, but her body betrayed her. Caught in the throes of self-pleasure, she can't resist the allure of her brother's unknowing display. As he enters, she's forced to confront her secret longings, her eyes drawn to his uncircumcised cock, her mind racing with visions of him fucking her deep and hard.