On the verge of exam season, a mother takes strict control of her son's ejaculation in hopes of improving his academic performance. Marking a calendar leading up to the test date, she enforces a rigid rule: only one ejaculation per day. To help him adhere to this rule, he receives special blowjobs as rewards from his young and attractive private tutor. However, if he ejaculates with anyone other than his mother, he is severely punished with a chastity belt. Gradually, the mother's own self-control reaches its limit, leading her to give in to incestuous desires. By the night before the exam, they end up having sex five times in a row.