What would you do if you discovered you were a character in a comic? And a supporting character at that? You’d change the course of the story, of course! It tells the story of Eun Dan-O (Kim Hye Yoon), a girl who realises she is a supporting character in the comic “Secret” and goes against the story, thwarting the author’s plans for her character by using the storyboard that only she can see, in order to win Ha-Roo’s (Rowoon) heart and change her life. Eun Dan-O is a pupil at a prestigious school. Her family is wealthy, but Eun Dan-O has a heart condition. Her boyfriend, Baek Kyung (Lee Jae-Wook), attends the same school. He is very keen on her, but she isn’t interested in him. Suddenly, Eun Dan-O suffers from short-term memory loss and finds herself able to see what will happen in the near future; she is confused. Then, Jinmiche (Lee Tae Ri), from the school canteen, tells Eun Dan-O that she is a character in the comic "Secret", just like everyone else. Eun Dan-O discovers that her character isn’t even a main character, but rather a supporting one, and that she doesn’t have much time left to live. Eun Dan-O is stunned, but decides she wants to find her real first love, not someone created by the writer. One day, she falls down the school stairs. She feels her back brush against the back of another pupil, amongst a group of boys. Her heart suddenly starts fluttering. Eun Dan-O wants to find the student who made her heart flutter. She eventually finds him (Ro Woon) and discovers he is her classmate. He is a character with no name, nicknamed "Number 13", and he too is a supporting character in the story. They approach each other and Eun Dan-O calls him "Ha-Roo". Meanwhile, Yeo Joo Da (Naeun) is a poor but optimistic girl with a pretty face and a kind heart. She is an energetic character who always has a smile on her face despite the privileged students around her (she is the comic’s protagonist). Oh Nam Joo (Kim Young Dae) is a second-generation chaebol and the nation’s number one wrestler, also known for his good looks. He has all the hallmarks of a devilish bad boy, including a rude personality and hidden inner pain (he is the comic’s protagonist). Lee Do Hwa (Jung Geon Joo) is a friendly and charming young man. He always smiles brightly and acts playfully in front of others, but in reality he is a character who hides his loneliness and sadness. Jin Mi Chae (Lee Tae-ri) is a mysterious student whose real name, age, nationality and background are all unknown. He is instead known as "Jinmichae" (jinmichae is a banchan made from dried squid). The nickname stems from his tendency to always turn up whenever jinmichae is on the canteen menu. Because of his good looks, he is sometimes referred to as the unofficial fourth member of the school’s "flower trio", known as ‘A3’.