A man falls in love with his fiancée's friend, but be can't get off the feeling that someone is observing them.

Seong-jin, a conductor and Su-yeon, a cellist, are about to get married soon. But Su-yeon suddenly disappears, leaving just a farewell video. Mi-joo, who substitutes for Su-yeon as cellist, comes into Seong-jin's life. They start to get closer and have a secret relationship. But as their relationship grows deeper, they can't shake the feeling that someone is watching them. As the secrets reveal itself, the desires are unveiled.