Ninomiya, a plain office lady. From her day to day life, she was a relatively inconspicuous presence at the company. One day, on her way home from a drinking party, she is accosted by Sato, a senior office worker, and she ends up having sex with Sato. Sato only thought of Ninomiya as a convenient woman for her, but she knew that Ninomiya had two secrets. That means being a slut and being a married woman...