Mitsue is asked to take care of her family while her daughter and daughter-in-law are away on a trip. Despite her age, she still has a vibrant and energetic body. Perhaps because of this, she comes up with a plan to enjoy a forbidden "oyakodon" with her son-in-law and grandson—engaging in illicit relations under the guise of looking after the house. What unfolds is a scandalous arrangement where the three indulge together in her daughter's absence.