The drama starts with Han Tae-Woong (Hyun Bin), a quiet, 17 yr-old math genius, entering a prestigious high school. There he meets Kim Jeong-Kyu, also a genius in mathematics. The two immediately develop rivalry and tension, but later become best friends. Through their conversations, we learn that Jeong-Kyu is a big boxing enthusiast. Meanwhile, Tae-Woong stumbles upon a little girl being bullied in the street and saves her. The girl develops a crush on him and gives him her pager so that she can see him again, but they never exchange names or contacts. They promise to meet again soon, but this never happens.
In a highly anticipated International Math Olympiad, Jeong-Kyu fails to fulfill his father’s expectations, and commits suicide in shame. Tae-Woong, who wins the gold medal, struggles from guilt, as he feels like he is partly responsible for Jeong-Kyu’s death. From guilt, Tae-Woong quits school, leaves home, and disappears.
Eight years later, Tae Woong, now 25, is a nameless boxer, living a completely different life. He abandoned mathematics and pursued boxing in honor of Jeong-Kyu, but he still bears painful memories of his past. In a chain of events he meets Bo-Ra (Sung Yu Ri), a beautiful, but cold-hearted young lady. She is the daughter of a rich businessman, but has an incurable disease. After a chain of events, Tae Woong is hired as her chauffer. They end up falling in love, but Tae Woong discovers that she was the little girl that he met eight years earlier, and that she is Jeong-Kyu’s little sister. Tae-Woong struggles in pain about his relationship with Bo-Ra, and his returning memories of Jeong-Kyu.
Throughout the story the two learn to find true happiness by helping each other. Tae-Woong melts Bo-Ra’s heart with love and helps her open up her heart. In return Bo-Ra helps Tae-Woong with his painful memories of the past.