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?