Years after marrying and building a happy life in the city, wife Eriko still secretly harbors lingering feelings for her stepson, Kyō, whom her husband left behind in their hometown. During a summer of record-breaking heat, she returns with her husband to his rural roots. But for Eriko, accustomed to urban comforts, the sweltering, air-conditioner-free wooden house surrounded by dense forest proves far more oppressive than imagined. Unable to bear the heat, sweat pours from her neck, beads on her ample breasts, and drenches her entire body—this overwhelming sensation of sweat intensifying the twisted, forbidden bond between her and her stepson.