Husband and wife haven't had sex in a long time, and Ritsuko fills her daily loneliness with masturbation. Known in the neighborhood as a beautiful wife, behind closed doors she secretly indulges in nightly self-pleasure. One day, her son accidentally catches her in the act and, developing a strong interest in his mother, begins blackmailing her. From that point on, the son starts pursuing his mother's mature body as a new pleasure, giving rise to an incestuous relationship.