From the back cover:
Tsukiko, thirty-eight, works in an office and lives alone. One night, she happens to meet one of her former high school teacher, "Sensei," in a local bar. Tsukiko had only ever called him "Sensei" ("Teacher"). He is thirty years her senior, retired, and presumably a widower. Their relationship - traced by Kawakami's gentle hints at the changing seasons - develops from a perfunctory acknowledgment of each other as they eat and drink alone at the bar, to an enjoyable sense of companionship, and finally into a deeply sentimental love affair.