Yumiko takes her son, who attends university in Tokyo, on a hot spring trip during summer vacation. After her son moved to the city, she discovered her husband's infidelity, causing their marriage to rapidly deteriorate until it was essentially over—divorce was imminent. This trip was intended to inform her son about the divorce. During the journey, Yumiko confesses the truth. Realizing his mother is no longer bound to anyone, her son begins to desire her as a woman.