Heirs

Cha Eun Sang is a 17-year-old daughter of a mute housemaid of a wealthy family whose 17-year-old son, Kim Tan, she meets while looking for her never-do-well sister in the United States.

After being left stranded by her sister and having her passport taken away by the police, Cha Eun Sang accepts Kim Tan's offer of staying at his house.

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

Eun Sang and Ra Hael, Tan's fiancee who came to visit him in the U.S., return to Korea. Upon returning home, Eun Sang discovers that her mother has been evicted and has moved into her employer's home. Missing his family and Eun Sang, Tan returns to Korea, much to Won's dismay.

To his shock, Tan discovers that Eun Sang and he are living under the same roof. He shadows her as she helps her mother with her household duties. Unbeknownst to him and his brother, their father is keeping taps on their respective relationships with Eun Sang and Hyun Joo, and in response, has offered Eun Sang a scholarship to Jeguk High School, a school for the elite and wealthy.

Eun Sang and Tan begin their first day at Jeguk High School. While Eun Sang is introduced to the social class system of the school, Tan clashes with his former best friend, Young Do. Meanwhile, Tan and Won's relationship worsens as their father decides to introduce Tan to his company's board.

Young Do becomes suspicious of Eun Sang's social status and her relationship with Tan as he bullies a boy of a lower social class, leading to a physical fight between him and Tan. He threatens to expose Tan's secret of being an illegitimate child if he doesn't transfer to another school.

Tan confesses to Eun Sang that he likes her but she is reluctant to reciprocate because of their class differences. Eun Sang wants to reveal the truth about her poor background to the other students but is advised otherwise by her best friend, Chan Young. Meanwhile, Young Do disrupts his family's photo shoot by inviting one of the women his father is having a dalliance with.

Furious over Young Do's behavior towards Eun Sang, Tan initiates another physical fight with him. Eun Sang skips school the next day, upset over the trouble that Tan has got into because of her. Meanwhile, Ki Ae pretends to be Eun Sang's mother to attend a parent's meeting at the school, inadvertently helping to cement Eun Sang's lie about her family.

Young Do meets Ki Ae, Tan's real mother, for the first time and is surprised to also see Eun Sang arriving at Tan's home after school. The midterm exam results are released as the students prepare for school camp. Ra Hael requests for an end to her engagement with Tan in front of their parents in retaliation against his relationship with Eun Sang.

Despite his intention of not attending the school camp, Tan arrives to see Eun Sang, much to Young Do's annoyance. As the students return to school, the engagement between Ra Hael's mother and Young Do's father is announced. Meanwhile, Won is warned by his step-mother that Tan will become a majority shareholder on his coming birthday. Ki Ae discovers that Tan and Eun Sang are dating.

Eun Sang leaves the Kims' residence as her mother prepares to resign. Young Do discovers Eun Sang's secret about her mother working as a maid for Tan's family. Tan reveals his own secret about being an illegitimate child to Ra Hael in front of their parents, effectively ending their engagement. Meanwhile, Won is warned by his father to not pursue a relationship with Hyun Joo.

Tan leaves home after surprising his parents by revealing their family secret of his illegitimacy to Ra Hael and her mother. As the other students find out about Tan and Eun Sang dating, Tan decides to put a stop to the bullying ritual of the lower social class students. Young Do confesses to Eun Sang that he likes her and threatens to reveal Tan's secret to the entire school.

Tan and Young Do are forced to confront their past as they are caught up in a fight yet again. While visiting Tan's mother to assure her that she doesn't want the engagement to be canceled, Ra Hael discovers Eun Sang's secret and plots to expose her in front of the other students during Chan Young and Bo Na's party.

Eun Sang deals with the aftermath of telling the other students the truth about her poor family. Meanwhile, Ki Ae blackmails Ra Hael's mother to cancel their children's engagement, which results in Tan's father placing Tan under house arrest. Rumors of Tan's illegitimacy spreads at school as Tan's father offers Eun Sang two choices.

To Tan's frustration, Eun Sang accepts the ultimatum set out by his father without a fight, while Young Do is upset by the other students' treatment of Eun Sang. Tan's father asserts control over his sons' lives by calling a stockholders vote to decide the fate of Won's position in the company.

Everyone is surprised by Eun Sang's sudden disappearance except for Tan's father. Eun Sang and her mother settle down at Gangwon-do and start to build a new life. Using their own methods, Tan and Young Do track Eun Sang down.

Young Do and Tan's family watch helplessly as Tan becomes despondent after deciding to give in to his father's wishes and let Eun Sang go. Ki Ae and Tan's father argue, resulting in Ki Ae's decision to separate. Moved by his brother's pain, Won helps Eun Sang to overcome her fear of returning to Seoul.

To his father's disapproval, Tan invites Eun Sang as his date to his 18th birthday party. Ki Ae moves in with Eun Sang's mother who is coaxed into approving Tan dating her daughter. Young Do locates his mother as the authorities prepare to prosecute against his father for improper business practices.

Tan and Won's stepmother gathers her allies to vote their father out of the company. To gain a vote for his father, Won chooses an arranged marriage with one of the major shareholders' daughter over Hyun Joo. Young Do reunites with his mother as his father is arrested. Tan's father wakes up from his coma as Tan and Eun Sang reflect on the past year and how far they've come together.