Saho lost her husband five years ago, but she is a sociable woman and now has a new boyfriend and is considering remarrying. Saho has a 40-year-old son, Shinichi, living with her. Although the mother-son relationship is not bad, Saho wants Shinichi to become independent and move out of the house as soon as possible, as he leads a self-indulgent lifestyle. In early autumn, the two of them went on a trip to a hot spring. They had originally planned to go with Saho's boyfriend, but he was suddenly unable to go, so she took her son instead. Little did they know that this trip would greatly change the fate of the two of them.