Kang Tae-Joon (Minho) is a gold medalist in the high jump, but he has been mired in a slump due to an injury. In order to help her idol, a girl named Koo Jae-Hee (Sulli) disguises herself as a boy and enrolls at the same all male high school.
When Tae-Joon (Minho) is competiting at the World Junior Competition, Jae-Hee (Sulli) watches him on TV in America and becomes very touched.
Despite her friends telling her otherwise, Jae-Hee cuts her long hair by herself. She then flies to South Korea, with a plan to stay with Tae-Joon who is now injured. Jae-Hee disguises herself as a boy and enrolls at the all boys Genie Physical Education High School. On her first day at school, Jae-Hee goes up the stairs with her suitcase, but her suitcase bursts open and all her clothes fall out. A boy comes by and helps her pick up her stuff. Jae-Hee realizes that the boy helping her is none other than her idol Tae-Joon. In her excitement, Jae-Hee sits on her suitcase, which proceeds to slide down the stairs.
Jae-Hee gets to her first class and introduces herself. One of her classmaste, Jong-Min (Hwang Kwang-Hee), tells her that if she wants to become their classmate she will have to go pickup a ball that sits inside a doghouse located on campus. Jae-Hee goes to the doghouse and sees a warning sign about the dog. Nevertheless, the dog seems friendly to Jae-Hee and she goes inside to take out the ball. At that moment, Jae-Hee hears Tae-Joon voices and she hides in the doghouse. Tae-Joon starts to talk to the dog and tells the dog that he doesn't want to perform the high jump at tomorrow's commercial shooting. Tomorrow will be the first time Tae-Joon does the high jump after suffering from his injury. Jae-Hee comes out of the doghouse and asks Tae-Joon if he is ok after his injury. Tae-Joon becomes angry and leaves.
She goes back to the classroom and gives the ball to Jong-Min, who is very surprised. The dog is normally hostile to guys that come by. Eun-Gyeol (Lee Hyun-Woo), who is a soccer player, looks at her with a smile.
Later, Jae-Hee goes to her dorm room and learns that she is sharing her room with one other student. When she gets out of the shower, Jae-Hee sees her new roommate, who is Tae-Joon! Tae-Joon immediately kicks her out of the room, but with the help of Seung-Ri (Seo Jun-Young), the student dorm monitor, she is able to get back into the room.
The next day, students at Genie High School gather to play soccer. Tae-Joon tells Jae-Hee that if she makes a goal he will let her stay in his room. Jae-Hee tries hard to score a goal, but collides with Jong-Min and gets knocked out. Tae-Joon carries her to the school infirmary. Before she wakes up, Tae-Joon runs to the school gym where the high jump commercial will be filmed. Meanwhile, Tae-Hee wakes up and she knows that the school doctor knows that she is a girl.