Umi has a happy marriage but grows depressed because she and her husband cannot have a child. When her lustful brother-in-law Kyoichi visits for a memorial service, he relentlessly probes the desire hidden deep inside her. Telling herself she was merely swept along, she gives in to a one-time encounter. His caresses and powerful thrusts bring pleasure unlike anything her husband has given her, and before long she is surrendering to a secret affair with him.