The title story in this collection describes a period of just over a year in the lives of a mother and her fifth-grader son, Makoto, in a small Hokkaido city. Having divorced her husband, the mother took Makoto to Hokkaido to live with her parents, but the two of them are now on their own. Makoto's classmates think his mother is cool: she drives fast and can change her own tires with ease. She holds a job as a city worker, collecting payments of the interest-free loans extended to residents for living purposes.
One day she tells Makoto that she is thinking of remarrying. When summer rolls around, she goes on a trip with the man, leaving Makoto behind. The day of her scheduled return passes with no sign of her, and he goes to look for her. The car she was riding in with the man had flipped over, but it turns out she emerged unscathed from the accident.
In September Makoto's grandmother passes away and his grandfather falls ill. Perhaps due to the car accident, the relationship between son and mother also deteriorates. Makoto worries that his mother left the man she was seeing not of her own will, but because of something that he had done. The work skillfully captures the subtle process by which a boy casts aside the yoke of a mother whom he respects in his search for emotional independence. This two-story collection pairs the prizewinning work with Saidoka ni inu (Dog in the Sidecar), a mid-length story describing, from the perspective of a primary-school-age daughter, the lover who comes to live with her father after the mother leaves home.