Kim Sun-yi, an elderly woman in her sixties living in the US, receives a phone call about the sale of her old family home back in South Korea.
Returning to her homeland, she's met by granddaughter Eun-joo, and they drive back to the house in the country. Sun-yi recalls how 47 years ago, when she was a 17-year-old girl in 1965, she moved from Seoul
along with her widowed mother and sister Sun-ja to a remote valley to undergo a period of convalescence after suffering problems with her lungs.
The Kims lived in genteel poverty at the mercy of their arrogant landlord, Ji-tae, son of the business partner of Sun-yi's late father. Because of her delicate health, the beautiful yet introverted Sun-yi lives an isolated life without any friends.
One day, Sun-yi discovers a feral boy of about 19 in their yard. His blood type is unidentifiable, and he can neither read nor speak. Even though he behaves like a wild beast, Sun-yi's kindhearted mother adopts him and names him Chul-soo, assuming he's one of more than 60,000 children orphaned in the korean war.
At first, Sun-yi considers him a nuisance, but eventually has fun taming him according to a dog-training manual. She teaches him how to wait patiently before a meal, how to wear clothes, speak, write, and other human behavior so that he could one day live like a normal man. Chul-soo demonstrates unswerving loyalty and superhuman brawn, inspiring the envy of Ji-tae, who lusts after Sun-yi.
The two eventually become close; as Sun-yi opens her heart to Chul-soo, he in turn falls in love with her, the only person to ever show him affection. But their relationship is fraught with difficulties as Ji-tae begins to cause trouble. Feeling threatened, Chul-soo lets loose his bestial instincts and in their fear, the town villagers turn on him. In order to save the boy who risked his life to be with her, Sun-yi leaves him with a promise: "Wait for me. I'll come back for you.''.
In present day, Sun-yi walks into the shed to find Chul-soo sitting there, still as young as he was 47 years ago. He hands her the note that she wrote. She realizes that he's been waiting all along. He reads her a book she had asked him to read all those years ago, as she falls asleep. The next day, she wakes up with Chul-soo nowhere in sight, and leaves with her granddaughter. They receive a call from the county asking about the property. Sun-yi tells him that she's not selling the place. Chul-soo stares from afar as the car drives away.
