A sister and her brother are bound by a deep bond. In order to take care of her brother, who is a graduate student, her husband agrees to live with her. However, her husband is a salesman and is often away on a business trip for the next three days. One day, her sister gets drunk! She mistakes her brother's erect penis for her husband's and has incestuous creampie sex with him at home! She fills her vagina with thick semen. "Let's have sex again while he's away on a business trip," said her sister... but wasn't she drunk?