Nanami lives with her mother and lives with her husband at her parents' home. Recently, she has been having a hard time with her husband, who is so busy with work that he neglects his family. Then her older sister Keiko comes home to visit her husband Toru. After dinner, Nanami ends up alone with Toru and starts complaining about her husband, but Toru is also troubled by their cold relationship... The two of them grow closer as they share a common problem, and the two of them, who are in an unforgivable relationship, cannot suppress their desires and become immersed in a double affair.