When Minhyuk, a professor of the music faculty goes to the practice room to find the violin he left there, he finds a student playing an imperfect but alluring performance with Minhyuk's violin. Feeling charmed by the student, "Hanbin", he starts to pay more attention to him in class. When he overhears that Hanbin is looking to withdraw from school due to his family's circumstances, Minhyuk offers a room in his house. Yet a strange atmosphere begins to cloud Minhyuk's family of three after Hanbin begins to live with them. Not only does his son Hyunjae seem to have a bad past with Hanbin, Minhyuk starts to feel distant from his wife Minjoo. Will bringing Hanbin to his house have been the worst mistake of his life, or the best mistake?