Mizue Nishio is a 50-year-old housewife living peacefully with her husband and son. However, she harbors a secret she can't tell her husband—their relationship has crossed the boundary of mother and child. One day, she sees her son walking arm-in-arm with a girl in front of the station. The sight strikes her deeply, shaking her to the core. After that moment, she can no longer focus on household chores, and her daily life begins to fall apart.