Yu-Jin is your regular "Little Miss Tardy" who too often finds herself in trouble for her lateness. Today seems no different and once again it is another rush to school for Yu-Jin with her childhood friend; Sang-Hyuk. Unbeknownst to her, this day is different. Fate intervenes as she makes the acquaintance of a mysterious new student.

Jun-sang and You-jin's love begins to blossom as they keep on running into each other. In the meantime, Jun-sang becomes confused and shocked to find the same picture he has in You-jin's house.

You-jin waits for Jun-sang until late at night, but he never appears. The next day, she hears the shocking news that Jun-sang was killed in a car accident. Ten years later, You-jin is engaged to Sang-hyuk. She meets her friend Chae-rin's boyfriend Min-hyung, who looks just like Jun-sang.

Sang-hyun is unhappy that You-jin is working with Min-hyung but realizes that he cannot make her quit the work. When Chae-rin finds out that You-jin and her boyfriend work together, she feels threatened and makes up lies about her to Min-hyung.

Min-hyung takes the drunk You-jin to his hotel room and is surprised when she calls him "Jun-sang". The misunderstanding between the two deepens and Chae-rin sets fire to Min-hyung's anger towards You-jin.

You-jin is injured while trying to save Min-hyung, and her boyfriend Sang-hyuk is infuriated. When Min-hyung realizes that his girlfriend Chae-rin lied to him about You-jin, he asks her for some space in their relationship. Min-hyung and You-jin go together to a pond where she shared beautiful memories with Jun-sang when they were in high school.

Min-hyung and You-jin spend the night at the ski resort and Sang-hyuk and Chae-rin wait for them anxiously. The next morning, Sang-hyuk questions You-jin whether she truly loves him. When she is unable to answer him, Sang-hyuk coldly turns away from her.

You-jin tells Sang-hyuk that she cannot marry him, and at the same time, she assures Min-hyung that she cannot have a relationship with him. She begs Sang-hyuk to give her a chance to stand on her own. Sang-hyuk does everything he can to change her mind, while stepping up to Min-hyung and warning him to not shake her heart.

You-jin finally breaks up with Sang-hyuk when she realizes that she is completely in love with Min-hyung. Although everybody around her opposes her love, she tells herself that she can be happy as long as she is with Min-hyung. Meanwhile, Sang-hyuk refuses to eat or sleep.

You Jin

Min-hyung goes to Jun-sang's old house and meets Kang Mi-hee. Mi-hee assures him that Min-hyung is actually Jun-sang. Sang-hyuk calls Min-hyung as Jun-sang and warns him to stay away from You-jin. Meanwhile, Min-hyung takes You-jin to his car by force, and tells her that he is Jun-sang. Unable to believe his words, You-jin only looks into his eyes with sad tears.

Despite Min-hyung's confession that he is Jun-sang, You-jin does not believe him, thinking that he is only doing that to get her back. Meanwhile, seeing You-jin even in his missing pieces of memories, Min-hyung sadly sheds tears. Min-hyung decides to leave as he realizes that as long as he cannot fully remember his past, he can no longer linger around You-jin.

When You-jin finds out that Min-hyung is Jun-sang, she desperately runs out to find him and stop him from leaving. During her attempt, she nearly gets into a car accident, and Min-hyung jumps in and gets hurt instead.

Jun-sang recovers his lost memories partially, and shares them with You-jin. Although You-jin and Jun-sang spend a happy time together for the first time in ten years, they both have heavy hearts as they are unable to erase the pain they have caused their friends.

Jun-sang and You-jin finally make up with their friend. One day, Jun-sang realizes that the last missing piece of his memories concerns his father. Meanwhile, when Jin-woo hears that Min-hyung is Jun-sang, he cannot help but question whether Min-hyung is his long lost son.

You-jin and Jun-sang decide to get married and head for Chuncheon to her mother's house to get her approval. However, when You-jin's mother finds out that Jun-sang is Mi-hee's son, she firmly disapproves of them getting married.

Unable to change You-jin's mother's mind, You-jin and Jun-sang decide to have a secret wedding by themselves. However, their plan is shattered when Sang-hyuk chases after them.

You-jin discovers a shocking secret from Kang Mi-hee. Meanwhile, Jun-sang treats You-jin coldly, knowing that he should cut ties with her. Realizing how difficult it must be for him, You-jin suggests to Jun-sang that they go their separate ways.

Jin-woo finds out that Jun-sang is his lost son. Jun-sang hears shocking news from the doctor that unless he undergoes brain surgery, he will have a very slim chance of living due to the aftermath of his car accident.