Sodamdo is a tiny island with two hundred residents, two hours by boat from the mainland. Seo Eunha, who guards the red-roofed post office alone, knows the names and stories of everyone on the island. Guest, who came to the island after burning out, has no one to send them letters. Yet, every afternoon, Eunha stops by Guest's house and says: "You've got mail." As for the sender, she says it's a secret.