Yeon-jung is an ordinary housewife living with her husband Jin-su, a typical family man. They have a daughter named Mina, a high school senior who has been pursuing her dreams of becoming a pianist. But it turns out, they have been deceiving one another as they quietly carry out their plans. Yeon-jung suddenly declares she’ll live her own life and jumps into the job market. Jin-su secretly spends his weekends in a secluded warehouse building something mysterious. Mina, who should be focusing on her piano lessons, suddenly shifts gears and starts to learn self-defense. As they continue their schemes under the radar, their secrets start to unravel, leading to disappointment and betrayal. In the end, they eventually realize each other‘s true motives. All three of them were trying to fulfill the promise they made to Seung-hyun, the elder son of the family, who also passed away in a tragic accident. With this truth, they rediscover their love for one another.