A sexy brother-in-law approached her? And he’s a younger man? Mi-yeon, who was adopted into her family when she was little, is living with her older sister, Si-yeon and Si-yeon’s husband. Mi-yeon’s desire towards her brother-in-law grows more and more every night when she gets to watch the affectionate interaction between her older sister and the brother-in-law. One day, Mi-yeon seduces her brother-in-law and the two end up crossing the line when they should not have. As the situation goes on, Mi-yeon finds out her older sister is also having affairs outside the marriage. Mi-yeon tries to clear up the relationship with her brother-in-law out of guilty feeling. However, she hears something shocking from the brother-in-law.