This drama portrays the life of the 19th king of Goguryeo, Hwanwoong, who was sent from the heavens to make the world a better place. He falls in love with Saeoh and gives her the joojak necklace; however, Kajin becomes jealous since Saeoh has given birth to Hwanwoong's son. She takes the baby and throws him off a cliff. Saeoh, thinking that her son had died, is overcome with grief and turns into the black joojak to destroy the world. Hwanwoong is the only one who could stop her. Afterwards, Hwanwoong returns to the Heavens and prophecizes that 2000 years later, the true Joo Shin king will come to Earth. With the help of the four gods, he will rebuild Joo Shin.

Winter Sonata begins when Joon-sang (Bae Yong Jun) moves to a new high school in search for his biological father. Yu-jin (Choi Ji Woo) and Sang-hyuk (Park Yong Ha) have been close childhood friends; though Sang-hyuk wants to be more than a friend, Yu-jin sees him merely as a brother. On a trip together with some other high school mates, Oh Chelin (Park Sol Mi), Jin-suk (Lee Hye Eun) and Yong-kuk (Ryu Seung Soo), Yu-jin is saved after an accident by Joon-sang and after that they get to be really close and she opens up his cold heart. However, circumstances and fate dictate that their love will never be. He abruptly disappears from their lives.

Ten years later the old High School buddies get together to celebrate Yu-jin and Sang-hyuk's soon to be wedding. Yu-jin who was deeply in love with Joon-sang, still has this fire in her heart for him, even though he's been out of her life for a decade. But at this party Oh Chelin's new boyfriend arrives, and he looks just the same as Joon-sang. Could it be him or is Yu-jin only dreaming?