Natsumi is an editor at a major publisher and her husband, Kazuhiro, works at a rival company. After 8 years of marriage, they have no children, and Natsumi still uses her maiden name. Little does she know that young postman Naruo stares longingly at her every time she comes by. One night, Kazuhiro makes a confession: He is having an affair with Fuyuko, a college student.

Natsumi is at work when she realizes she left her phone. At that very moment, Naruo rings her and Kazuhiro, who dropped by the house, picks up. Kazuhiro grows suspicious. Why was the "post office" calling Natsumi? Later that night, Natsumi dines with colleagues at the office as Kazuhiro strolls in unexpectedly with Shohei, an up-and-coming author.