Four years into a happy marriage, Saki still struggles with her relationship with her husband's adult son Shota. After graduating from college, he moved to Tokyo as if avoiding her and stayed away for three years. One summer he suddenly returns to the family home just as her husband leaves on a week-long business trip. Alone together and seeing how withdrawn Shota has become, Saki resolves to support him as his stepmother, only for their closeness to turn into a forbidden summer affair.