Souko Sasaki has lived in an unhappy marriage for years and still remembers her former lover. Knowing about her husband's affair, she gets into one as well. During a trip with her lover, she meets a woman who looks exactly like her. To her surprise, this woman is also named Souko. She also discovers that her doppelganger is the wife of none other than her former love, Shunichi Kawami. Soon, dissatisfied with their plight, the women decide to use their striking resemblance and switch places once a month. However, they are unaware of how much the seemingly innocent game will cost them.