Byun Baekhyun is known as one of the many young professors at the university, and he doesn't like to get himself romantically involved with his students. Why? Because he didn't want to end up like his younger sister, Bomi, and his now brother-in-law, Joonmyun. He takes the student-teacher relationship rule seriously and never once has he made an attempt to break those rules for anyone. 

But what happens when he becomes conflicted with someone that he met during his break in America? What happens when she happens to appear in his class? What happens when she's his sister's best friend?

How is Baekhyun suppose to react to all of this?