Ai, a daughter-in-law, is begging her mother-in-law to see her grandchild. One day, her mother-in-law suggests they go on a trip to a hot spring. Ai is keen, but her mother-in-law orders her to conceive at the hot spring, and even makes her drink herbal tea that is said to increase sexual desire. On the day of the trip, the effects of the herbal tea make Ai so excited that she cannot be satisfied with sex with her husband. Meanwhile, her father-in-law is also full of energy and tries to make love to his mother-in-law, but she refuses. As they are both in a state of arousal, the father-in-law accidentally sees Ai naked and cannot control himself...