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 and Kazuhiro, post-separation, bump into each other at an author's funeral. The two have dinner, reconnecting over work, books, and many, many drinks, ending with them in bed together.The next day, Natsumi's best friend Kyoko ask her why she'd get back with her husband despite having a new young lover. Natsumi makes a bold decision.

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.