1 Cha Eun Sang, the 17-year-old daughter of a mute housekeeper, travels to the United States to find her ne'er-do-well sister, and meets Kim Tan, the 17-year-old son of the wealthy family her mother works for.

2 Left stranded by her sister and stripped of her passport, Eun Sang accepts Kim Tan's offer to stay at his house.

3 Trying to delay Eun Sang's return to Korea, Tan takes her along to meet his half-brother Won, who has arrived in the U.S. on a business trip. Meanwhile Eun Sang's mother, Hee Nam, overhears her employer's mistress, Ki Ae, talking about getting rid of his second wife.

4 Eun Sang and Rachel, Tan's fiancée, return to Korea. Back home Eun Sang finds that her mother has been evicted and has moved into her employer's house. Missing his family and Eun Sang, Tan follows them back, much to Won's dismay.

5 Tan discovers that he and Eun Sang are living under the same roof, and shadows her as she helps her mother with the housework. Unknown to either brother, their father has been keeping tabs on their relationships with Eun Sang and Hyun Joo — and has offered Eun Sang a scholarship to Jeguk High School.

6 Eun Sang and Tan start their first day at Jeguk High. She is introduced to the school's social pecking order while Tan clashes with his former best friend, Young Do. Tan and Won's relationship worsens as their father decides to present Tan to the company's board.

7 Young Do grows suspicious of Eun Sang's standing and her closeness to Tan as he bullies a boy from a lower class, and the two come to blows. He threatens to expose Tan's secret unless he transfers to another school.

8 Tan tells Eun Sang he likes her, but she holds back because of the gap between them. She wants to tell the other students the truth about her background; Chan Young advises against it. Young Do disrupts his family's photo shoot by inviting one of his father's lovers.

9 Furious at the way Young Do treats Eun Sang, Tan picks another fight with him. Eun Sang skips school the next day, upset at the trouble she has caused him. Ki Ae poses as her mother at a parents' meeting, inadvertently cementing Eun Sang's lie.

10 Young Do meets Ki Ae, Tan's real mother, for the first time, and is surprised to see Eun Sang arriving at Tan's house after school. Midterm results are released as the students prepare for school camp. Rachel asks to end her engagement to Tan in front of both sets of parents.

11 Despite meaning to skip the school camp, Tan turns up to see Eun Sang, to Young Do's annoyance. The engagement between Rachel's mother and Young Do's father is announced. Won is warned by his stepmother that Tan becomes a majority shareholder on his coming birthday, and Ki Ae works out that Tan and Eun Sang are dating.

12 Eun Sang leaves the Kim residence as her mother prepares to resign. Young Do learns that Eun Sang's mother is the family's maid. Tan reveals his own secret — that he is an illegitimate child — to Rachel in front of their parents, ending the engagement. Won is warned by his father not to pursue Hyun Joo.

13 Tan leaves home after telling Rachel and her mother the family secret. As word spreads that he and Eun Sang are dating, he sets out to stop the school's bullying ritual. Young Do tells Eun Sang he likes her, and threatens to tell the whole school about Tan.

14 Tan and Young Do are forced to face their past when they fight again. Visiting Tan's mother to insist she does not want the engagement called off, Rachel discovers Eun Sang's secret and plots to expose her at Chan Young and Bo Na's party.

15 Eun Sang deals with the fallout of telling the other students the truth about her family. Ki Ae blackmails Rachel's mother into calling off the engagement, and Tan's father puts him under house arrest. As rumours of Tan's illegitimacy spread, his father gives Eun Sang two choices: leave now and go anywhere she likes, or leave in two weeks and let him decide where.

16 To Tan's frustration, Eun Sang accepts his father's ultimatum without a fight, while Young Do is troubled by the way the other students treat her. Tan's father asserts control over his sons by calling a shareholders' vote on Won's position in the company.

17 Everyone but Tan's father is surprised by Eun Sang's sudden disappearance. She and her mother settle in Gangwon-do and begin a new life. Tan and Young Do each set about tracking her down their own way.

18 Young Do and Tan's family watch helplessly as Tan sinks into despondency after giving in to his father and letting Eun Sang go. Ki Ae and Tan's father argue, and she decides to separate. Moved by his brother's pain, Won helps Eun Sang overcome her fear of returning to Seoul.

19 Against his father's wishes, Tan invites Eun Sang as his date to his eighteenth birthday party. Ki Ae moves in with Eun Sang's mother, who is coaxed into approving of Tan. Young Do finds his mother as the authorities prepare to prosecute his father. When Tan's father falls into a coma, his stepmother seizes the chance to take over the company.

20 Tan and Won's stepmother gathers her allies to vote their father out of the company. To win a vote for his father, Won chooses an arranged marriage with a major shareholder's daughter over Hyun Joo. Young Do is reunited with his mother as his father is arrested. Tan's father wakes from his coma as Tan and Eun Sang reflect on how far they have come.