Yuka marries a man who already has an adult son, Shinichi, and the two maintain a warm, trouble-free relationship. Her life looks perfect from the outside, but sex with her low-libido husband has neither given her the child she wants nor satisfied her own desires. When her husband leaves on a long business trip, she suddenly finds herself living alone with Shinichi. Everything goes smoothly at first, but his physical contact gradually increases. Yuka dismisses her unease as imagination until his advances become unmistakably brazen.