The day before her wedding, the female protagonist catches her fiancé cheating. To comfort her critically ill grandmother, she hastily changes groom and enters a flash marriage with the male protagonist, who has also been betrayed. Hiding his identity as a CEO and pretending to be an ordinary employee, the two agree to a secret marriage without developing feelings for each other. However, while pretending to be a couple in front of Grandma, the male protagonist realizes that she is the girl who saved him with her singing back in high school, and his frozen heart gradually melts. She also falls for him under his gentle protection. After his identity is exposed, he fights back for love and breaks free from family control. In the end, he makes up for the proposal in the piano room where they first met, fulfilling his promise to love her forever.
