"The Heirs" depicts the friendships, rivalries and love lives of young, rich heirs led by Kim Tan (Lee Min-Ho) and a girl named Cha Eun-Sang (Park Shin-Hye). Unlike the others, Cha Eun-Sang is considered ordinary and comes from a poor background.
18-year-old Cha Eun-Sang lives with her mother who is mute. Her mother works as a housekeeper and Eun-Sang also works part-time jobs to help out. One day, Eun-Sang's older sister (Yoon Jin-Seo) calls from the U.S. and informs them that she will marry. Eun-Sang's mother then asks Eun-Sang to send her older sister some money from her savings account. Eun-Sang isn't happy with her situation and decides to go to the U.S. herself to see if she can start a better life with her sister.
When Eun-Sang arrives in California she is in for a shock. Her older sister lives in a filthy home with a deadbeat boyfriend who seems violent. Her sister is also not getting married or going to school and works full-time as a waitress. When Eun-Sang finally tracks down her sister working at a beach front restaurant, she takes the money Eun-Sang brought for her wedding and leaves without even saying goodbye. Eun-Sang's dreams of starting a better life in America quickly vanishes and she crumbles to the ground in tears.
Meanwhile, Kim Tan is not your typical high school student, but a handsome and wealthy Korean heir to a large conglomeration. He is sitting out on the patio of the beach front restaurant, watching everything unfold between Eun-Sang and her sister.
Kim Tan's American friend then sees a ziplock bag with a powdery substance fall out of Eun-Sang's suitcase and runs over to scoop it up. Kim Tan knows immediately that the ziplock bag doesn't contain drugs, but rather powder grain to make traditional Korean drinks. Soon, Eun-Sang runs off after Kim Tan's friend and Kim Tan goes to help Eun-Sang.
When the dust is settled, Eun-Sang walks out of a police station and her passport is temporarily confiscated. With nowhere to go for Eun-Sang, Kim Tan offers to let her stay at his home. Although they seem to come from different worlds, they quickly develop a rapport for each other. But, when Kim Tan is at school, Eun-Sang meets a girl named Rachel (Kim Ji-Won). Rachel informs Eun-Sang that she is Kim Tan's fiance and she demands that Eun-Sang leaves his home immediately. Eventually, Eun-Sang returns to South Korea.
Kim Tan now feels nothing but emptiness after Eun-Sang's departure. He decides to go back to Korea even though his older stepbrother Won (Choi Jin-Hyuk) strongly opposes his return. When Kim Tan gets back to his luxurious mansion like home, he sees someone briefly that resembles Eun-Sang. Kim Tan goes to his mother Ki-Ae (Kim Sung-Ryoung) and asks about the unfamiliar, but familiar girl that he briefly saw.
His mother tells him that the girl is their housekeeper's daughter and her name is Cha Eun-Sang. She's also staying in their home.
Kim Tan is heir to the Empire Group sent to study abroad in the U.S. In reality it's a form of exile, as his elder half-brother back home schemes to take over the family business. While in the States, Kim Tan bumps into Cha Eun Sang, who arrived from Korea in search of her older sister. He feels himself falling for her, never realizing that she's the daughter of his family's housekeeper. When his fiancée Rachel Yoo arrives to bring him back to Korea, his heart is torn between love and duty.
