Original: 졸업
A secret and sweet real-life romance between veteran academy instructor Seo Hye-jin and her flirty student Lee Joon-ho, who returns after 10 years and stirs her heart.
Famous star instructor Seo Hye-jin works until midnight at the academy like any other day. As she stares at the Hall of Fame in the lobby, Joon-ho's name catches her eye. He is one of her proud boast as she did her best to teach him, and he made it into a prestigious university. At the same time, Joon-ho decides to resign from his company and make a new beginning as a rookie instructor.
Even though Hye-jin tries to dissuade Joon-ho, he already passed the first written exam and is getting ready for the test lecture. Therefore, Hye-jin privately asks Ji-seok to disapprove of him. Meanwhile, Sang-sub, the Korean language teacher at Chanyoung High, makes a declaration that creates huge confusion among the students and academies.
A clandestine endeavour dubbed "Teacher and Student Sally Forth" sparks a covert tutoring session led solely by Hye-jin for Joon-ho. Alone in an office after hours, they exchange determined gazes as they delve into a specialized lesson. Meanwhile, the renowned Director Choi, also known as the White Haired Witch, sets her sights on expanding her academy.
Hye-jin and Joon-ho's optimism for their collaborative lecture fades as they discover only one student has attended their free session. Shocked, Hye-jin collapses emotionally while Joon-ho supports her in regaining composure. They soon learn of a tactic by Choi Sun Academy to dissuade students from considering switching, but the lone attendee might just potentially change the game.
Director Choi Hyung-sun, the White Haired Witch, finds out that Hye-jin and Joon-ho taught the class even though there was only one student. She checks on Si-woo to see if he wants to switch academies and asks about the lecture. After hearing about the lecture, she calls Hye-jin to meet up. Meanwhile, Joon-ho asks Hye-jin not to leave the academy and stay with him for at least a year.
Joon-ho finds out that Hye-jin has been helping him out by taking a loss. He tells her that he'll work on his own, and Hye-jin gets strange feelings from his attitude. Meanwhile, the new class opens, and Director Kim gets in an awkward position because his plan to demote Hye-jin fails. He feels worried about Hye-jin leaving the academy. He calls Hye-jin out to talk about it. And Joon-ho tags along with her.
Joon-ho confesses his feelings for Hye-jin and he wants to know what she thinks about him. However, an unexpected visit takes his chance away. Joon-ho wants to talk about it the next day, but Hye-jin has to go and see the director who got hungover. Hye-jin decides to leave the academy and move to Choisun. But after running into Si-woo, she remembers something that she had forgotten about.
Hye-jin tells the director that she won’t leave the academy and teach the Heewon High class. Hye-jin goes to So Young’s office and talks about her decision and what she thinks about Joon-ho with her. After having some beer, she finally confronts her true feelings. Joon-ho comes to take her home, and the two finally confirm their feelings toward each other.
Hye-jin and Joon-ho become more intimate, and the two enjoy dating in secret at the academy. The exams are over, and the teachers are busy checking the results of the students. Si-woo comes to the academy and talks about his concerns. Joon-ho becomes more determined to help Si-woo get good grades in Korean. Meanwhile, an unexpected visitor comes to see Hye-jin.
Pyo Sang-seob tells Hye-jin that he will be teaching at Choisun Academy. He tells her that the mid-term incident made him think about being a teacher, and it led to quitting his job and starting a new career. Hye-jin is shocked to hear the news though she had an argument with him, she still had respect for him. Meanwhile, Joon-ho doesn’t have a clue why Hye-jin feels complicated about Sang-seob.
Joon-ho’s parents meddle in his work and try to help him become successful in their ways, but Joon-ho feels uncomfortable about it. Seung-hui feels threatened by Hye-jin who is getting all the support from the director. She meets up with Hyung-sun to talk about their future. Meanwhile, Jun-ho wants to open a class that teaches how to read to the students. However, Hye-jin finds it too idealistic.
Sang-seob tells Hye-jin that someone copied her teaching material to use it against her. Joon-ho and Hye-jin’s argument continues, and it gives Sang-seob food for thought. Hye-jin decides to support Joon-ho, but the academy doesn’t approve of opening a new class. Meanwhile, Seung-hui invites Hye-jin to dinner to talk about their future together.
Hye-jin decides to give up her teaching materials and turn down the vice-director’s offer to leave the academy with her. However, Hyung-sun reveals Hye-jin and Joon-ho’s relationship, and Seung-hui decides to use it to her advantage. Meanwhile, one of the instructors who found out about Hye-jin and Joon-ho gathers a meeting to talk about the spreading rumors.
Hye-jin and Joon-ho decide to face the situation with no lies, but they are worried and feel sorry for the people who will be harmed because of them. The other instructors are complaining about the possible privileges that Joon-ho might have earned from Hye-jin. The rumors spread to the students and parents, and it damaged Hye-jin’s reputation. To save the academy from falling apart, Hyun-tak suggests Joon-ho leave the academy.
Joon-ho talks about how frustrated he was when he realised that there was nothing he could do to help Hye-jin. Hyun-tak is worried about managing the academy as students are leaving after Hye-jin and Joon-ho’s scandal. Seung-hui meets up with other instructors to have them on her side, and Joon-ho decides to face Seung-hui himself to solve the matter.
Some instructors leave the academy, and some request to meet Hyun-tak to talk about their plans. Seung-hui reaches out to Min-jin and asks her to be her spy in Choi-sun and betray Hye-jin. After discovering what Seung-hui did, Hye-jin decides to face the one behind all the schemes around her. As she goes through the struggles, she thinks about what she really wants to do.
