Mio Kimijima is a modest married woman living with her husband, both of them working full-time. On top of her regular five-day job, she also takes on part-time work to make ends meet. However, she secretly begins a hidden affair with an older male coworker from her part-time job, meeting him in public restrooms after work. Lured by the promise of "a raise in your hourly wage," she repeatedly meets the middle-aged man in the station bathroom, indulging in pleasure day after day. Her husband naively celebrates her increased income, completely unaware that his wife is being emotionally and physically consumed by these daily encounters, gradually succumbing to temptation and falling deeper into sin.