It tells an unpredictable 24-hour love story of the four-dimensional innocent girl Jung Saet Byeol who was once a troublemaker and the adorkable caring male store manager, Choi Dae Hyun, in the context of a convenience store. They have met each other accidentally 4 years ago, back then Saet Byeol asked Dae Hyun to buy cigarettes for them. Until now, Saet Byeol comes to the convenience store Dae Hyun runs for a part-time job, their hilarious romantic story starts.
In the past, Dae-Hyun is a good looking, down-on-his luck man whose girlfriend has just broken up with him while Saet-Byul is a strong, charismatic schoolgirl who is good at fighting.
Yeon-Joo, Dae-Hyun's girlfriend, sees him drinking with Saet-Byul and her friends. The police arrive accusing Dae-Hyun of selling cigarettes to a minor.
Yeon-Joo's jealousy grows as she learns that Saet-Byul, the part timer Dae-Hyun hired, is good looking from a coworker. Angry with rude customers, Saet-Byul gets into a fight with them and is seen by Dal-Shik, Dae-Hyun's best friend.
Dae-Hyun misunderstood the situation between Yeon-Joo and Saet-Byul in the bathroom. Saet-Byul runs into the celebrity, and her old friend, Kang Ji-Wook, who her father used to train.
Though Yeon-Joo is jealous when she witnesses Saet-Byul getting a piggyback ride from Dae-Hyun, she still invites her out to eat with them.
Saet-Byul is attacked in retaliation. Dae-Hyun is close by and rushes to her aid. Despite that, Saet-Byul is fine but needs surgery for her appendicitis.
Saet-Byul tells Dae-Hyun she's quitting. Saet-Byul and Eun-Byul are forced from their apartment after they find out they and several others in the building have been scammed.
Saet-Byul winds up sleeping at the Choi family home for the night, startling Dae-Hyun. She's invited to stay until she finds another place.
Yeon-Joo is annoyed to find out that Saet-Byul is living with and well liked by the Choi family. Yeon-Joo and Dae-Hyun get into a fight.
Dae-Hyun is heartbroken when Yeon-Joo breaks up with him and leaves with Seung-Joon. While the two go out the drink, Dae-Hyun returns to the store for work. Eun-Byul is found out when Saet-Byul witnesses her with her girl group.
Saet-Byul confesses to a sleeping Dae-Hyun that her feelings for him go back longer than the 3 years he remembers.
Dae-Hyun is startled by Ji-Wook's easy confession about his feelings for Saet-Byul. He feels inferior compared to the celebrity Ji-Wook during the filming. He's happy to hear Saet-Byul call him handsome. Saet-Byul and her friends support Eun-Byul's debut. Meanwhile, Geum-Bi and Dal-Shik deal with the falling out from their almost dating. Eun-Byul seeks help from Ji-Wook.
Saet-Byul witnesses Yeon-Joo and Dae-Hyun outside of the store and gets jealous. She goes to see Eun-Byul but winds up in a fight. Dae-Hyun takes care of her injuries. Meanwhile, Dal-Shik and Geum-Bi run into each other.
Dae-Hyun gives Saet-Byul flowers to wish her luck on her upcoming GED exams. Yeon-Joo witnesses this but remains resolute in her intentions to get back together with Dae-Hyun, leading to a fight with her mother. Eun-Byul has a brief but welcomed reunion with Fancy Girls.
Saet-Byul turns Dae-Hyun down by telling him she give her answer later, after she passes the GED. Dae-Hyun meets Jang-Mi who is his father's first love. Saet-Byul gets good news. Meanwhile, Dal-Shik and Geum-Bi continue getting to know each other.
Dae-Hyun finds out that Saet-Byul moved out without saying anything and worries about her. She gets a job working at a greenhouse while Dae-Hyun searches for her.
