Han Jung-suh (Park Shin-hye) and Cha Song-joo (Baek Sung-hyun) are childhood friends and have a special bond that blossoms into love. They both share the pain of losing a loved one: Song-joo’s father died in a traffic accident and Jung-suh’s mother died of eye cancer. Jung-suh’s father (Ha Jae-young) marries an actress named Tae Mi-ra (Lee Hui-hyang), who brings her real daughter, Han Yoo-ri (Park Ji-Mi), and son, Han Tae-hwa (Lee Wan) into the household. Yoo-ri is jealous of Jung-suh, making her look terrible in front of her mother, who begins to turn on Jung-suh. When Jung-suh’s father leaves for work, her stepmother assaults her. She thwarts Jung-suh’s attempts to study abroad with Song-joo, who then leaves for America alone. Mi-ra plots for Yoo-ri to win the affections of Song-joo who is the heir of his family fortune. All the while, Jung-suh tries to be nice to Tae-hwa, but he mistakes her friendship for something more, and falls in love with her.
Three years later, Song-joo (Kwon Sang-woo) comes back from America, and Jung-suh (Choi Ji-woo) rushes to greet him. A jealous Yoo-ri (Kim Tae-hee) tries to stop them from reuniting. As they race to the airport, Yoo-ri intentionally hits Jung-suh with her car. Jung-suh is taken to the hospital where a group of people had just died in fire. Yoo-ri swaps Jung-suh’s ID with one of the people to fake her death. She takes the real Jung-suh to her biological father’s home. Tae-hwa (Shin Hyun-joon), still in love with Jung-suh, finds out what Yoo-ri has done, but seizes the opportunity to run away with Jung-suh. Jung-suh loses her memory, and Tae-hwa moves them away and changes their names.
Five years later, Yoo-ri is soon to be engaged to Song-joo. Song-joo decides that he needs to let go of Jung-suh and goes to the carousel they used to ride as children. He wishes to see Jung-suh just once more, looks up, and sees her on the carousel. Jung-suh, now named Kim Ji-soo, works at a small clothing shop while living with Tae-hwa (now Chul-soo). Song-joo rushes to Ji-soo and tells her that she is Jung-suh, but she doesn’t believe him. Song-joo is determined to make her remember her past, and through a series of events, he and Jung-suh become close.
Jung-suh regains her memory when Yoo-ri nearly hits her with her car again and rushes to tell Song-joo. She forgives Tae-hwa as she knew he did it out of love. Jung-suh and Song-joo are happy together, until she discovers she has eye cancer. She asks Tae-hwa to take her away from Song-joo, since she can’t bear to see him in pain. Gradually, Jung-suh’s vision deteriorates into blindness. Tae-hwa tells Song-joo and his family the truth starting from the accident. Yoo-ri is arrested, and her mother goes insane and is admitted to a mental hospital.
Song-joo marries Jung-suh, who is now blind, with the blessing of his mother and her father. Jung-suh tells Tae-hwa that her one wish is to see Song-joo’s face one last time. Both Song-joo and Tae-hwa ask a doctor to let them give Jung-suh one of their corneas, but the doctor tells them that they can’t take corneas from live donors. Tae-hwa wants to grant her wish at all cost and commits suicide via car crash in order to donate his cornea to her. After his death, Jung-suh has the operation and is able to see again. However, Song-joo finds out about Tae-hwa’s death and later on tells Jung-suh. She starts to feel sick again, and the doctor states that the tumor has spread to her brain and is inoperable; the same incurable illness that killed her mother. Jung-suh, realizing this, forgives Tae Mi-ra and Yoo-ri because of Tae-hwa. Both Yoo-ri and Tae Mi-ra feel remorse for their sins against Jung-suh, and apologize to her. Jung-suh dies a few days later at the seaside near her childhood home, in the arms of Song-joo. The ending scene reverts to the beginning scene where Song-joo is playing his piano by the ocean of the memorable beach house. He says, “Perhaps, that person (Tae-hwa) might have loved that girl (Jung-suh) more than I. But even though I say this, that doesn’t mean that I loved her any less.”