Sayaka and Ikuo are a married couple in their second year of marriage. Sayaka is on the phone with a friend complaining that her husband has stopped inviting her out to the night recently, when her brother-in-law, Kiyoshi, who has just moved into the same apartment building, overhears them and pressures her into a physical relationship. Even though she knows it's wrong, she is swept away by her curiosity and Kiyoshi's aggressiveness, and falls into a swamp of pleasure...