Worried about her daughter who had returned to her parents' home after a fight with her husband, mother Reiko decides to stay at her son-in-law's house for a while. One night, while Reiko is taking a bath, her son-in-law accidentally opens the door and walks in, causing them to come face to face while both are naked. Awkwardness fills the air. That night, Reiko recalls the incident and indulges in masturbation, thinking about her son-in-law. Meanwhile, the son-in-law becomes obsessed with his stepmother's alluring figure and knocks on her door. A new, forbidden emotion begins to stir between them tonight.