Married for 25 years, Reiko feels uneasy as her husband starts caring more about his appearance. Feeling suspicious as his outings increase, she secretly follows him—only to find him meeting up with her own friend! While continuing her tailing in shock, she runs into Nakata, the friend's husband, who was also following them. They follow the pair into a hotel... and while listening through the wall of the neighboring room, resentment and lust swell within both of them. Thinking 'why not us too,' they finally give in to their desires and cross the line...