While delivering a student's dry cleaning, Geum Jan Di saves the life of a student at the most prestigious school in South Korea. Her actions soon became public and exposes the bullying within the school. To silence the public's attention, Jan Di is offered a swimming scholarship to Shinhwa High School which she declines but her family forces her to attend.
During her first day at Shinhwa, Jan Di learns of the famous F4 and of the other students' adoration and fixation with the boys in the group. Gu Jun Pyo, Yoon Ji Hoo, So Yi Jung, and Song Woo Bin are the richest and most powerful kids within Shinhwa and South Korea. Subsequently, they use their power to terrorize weaker students or those they do not like. Jan Di, instead of being impressed, becomes enraged and fantasizes about confronting Gu Jun Pyo, the leader and initiator of many of the bullying acts. She gains courage to confront him when a friend, Oh Min Ji, accidentally spills ice cream on his shoes and he demands the girl to lick it off. Jan Di defends her friend and attempts to reason with Jun Pyo's tyrannical demand. When he refuses to relent, Jan Di turns violent, knocking Jun Pyo to the ground. Engaged by this, Gu Jun Pyo declares war on Jan Di and encourages the other students to bully her. Jan Di, however, is resistant, refusing to apologize to Gu Jun Pyo, and stands by her decision to fight him.
Ironically, Gu Jun Pyo, having never been stood up to, begins to develop feelings for her. He tries unsuccessfully to woo her as she slowly begins to spend more time with Jun Pyo and his friends. Jan Di teaches Jun Pyo that money cannot buy everything and in order to have real friends, he himself must be real or use his heart, but Gu Jun Pyo still does not understand why someone like Jan Di should dislike him. As the story progresses, Jun Pyo falls deeper in love with Jan Di and she learns how to open herself to his love as well.
Jan Di's best friend, Ga Eul often finds herself in the same place as Yi Jung. Though she finds him attractive, she is initially annoyed by his arrogance. One day, Yi Jung finds Ga Eul crying after she is dumped by her boyfriend. He advises her to let him go, and later, to make her feel better, the two show up to a club in which he is attending. Yi Jung pretends to be in love with Ga Eul to make her ex jealous. He gives her his scarf and walks her home. After this, Ga Eul finds herself smitten with Yi Jung. On Valentine's Day, she waits outside his house, planning to give him chocolates. He shows up with two girls on his arm and on his table, he already has dozens of chocolates from other girls. When Ga Eul is upset, Yi Jung reminds her that their night at the club was only an act, and it's not his fault if she took it too seriously. Yi Jung feels bad, and gives Ga Eul a cake and flowers, when he mistakenly thinks it's her birthday. The two become friendly again.
As love begins to blossom between Jan Di and Jun Pyo, Jun Pyo's mother discovers them and deems it unsuitable. She does everything in her power to keep the two apart, even arranging a marriage for Jun Pyo. The other F4 members and Ga Eul try to bring them back together. Yi Jung and Song Woo Bin came up with a few plans, but they fail. They resort to So Yi Jung and Ga Eul pretending to go on a fake date, which upsets Jan Di because she doesn't consider Yi Jung good enough for her friend. She follows the two around with Jun Pyo by her side, making sure Yi Jung is treating Ga Eul appropriately. At first their plan was successful but because of Jun Pyo's mother, their relationship became strained again.
After their date, Ga Eul finds her self falling for Yi Jung again. Yi Jung feels the same way, but he can't bring himself to admit it, due to his doubt in true love. After a talk with the first girl Yi Jung loved, Ga Eul admits to Yi Jung how she feels about him and asks if he'll go on a real date with her. He rejects her, saying he doesn't date nice girls, foolish girls, or girls connected to his friends. He later changes his mind, and takes her out, though he spends all his time ignoring Ga Eul, and talking to other women. Their date ends with Ga Eul throwing water in Yi Jung's face, but Ga Eul still helps Yi Jung to get safely home when he is too drunk to do it himself.
Other factors keep arising as another member of the group falls in love with Jan Di (which was Yoon Ji Hoo) and in a twist of fate, Jun Pyo loses his memory. A girl named Jang Yu Mi which was on the same hospital where Jun Pyo was confined, takes advantage on him to make him fall in love with her. Geum Jan Di never gives up for Jun Pyo to remember his love for her, she falls in the swimming pool letting Jun Pyo reminise his love for her. On Jan Di's graduation, Jun Pyo proposes to her on the cable car at the NamSan Tower where their first date was held. Gu Jun Pyo told Jan Di that he needs to study abroad to fix problems regarding Shinhwa. Jun Pyo asks Jan Di to accompany him as his wife but Jan Di refuses because she has also plans for her future becoming a doctor. The two agreed but Jan Di told Jun Pyo that she will be waiting for 4 years in one condition--if Jun Pyo comes back as a handsome and charming man.
After Ga Eul helps Yi Jung decipher the message his first love tried to send him, Yi Jung has a change of heart about their relationship. At his home, Yi Jung warns Ga Eul that he's not a nice guy, and Ga Eul tells him that not every nice girl wants a nice guy. The two almost kiss, though they get interrupted. Later, Yi Jung visits Ga Eul to talk about their relationship. Before Yi Jung can confess how he feels for Ga Eul, she cuts him off, thanking him for giving her the chance to not have any regrets about the two of them, since she gave it her all. She leaves him before he ever gets the chance to say he loves her.
The story ends with F4 four years later with each cast revealing happenings on their current life--Yi Jung coming back form Sweden for helding his art exhibit and visits Ga Eul to a kindergarten teacher, where it's revealed that the two are now dating, Ji Hoo who just opened his Grandpa's clinic, and Woo Bin becoming a happy man but his career was never mentioned in the story. Lastly, Geum Jan Di went to the beach to see Jun Pyo.He then proposes to Jan Di but the answer was still a question among viewers because when Jan Di was about to answer--Ji Hoo, Yi Jung and Woo Bin arrives saying that they object to the proposal because Jun Pyo and Jan Di didn't ask for their permission first....and they live peacefully.