In 2002, on the night of Korea's momentous World Cup win, high school sweethearts Jang Guk (Lee So-yeon) and Yu Jun-su (Namkoong Min) sleep together and Jang Guk ends up pregnant. They are given permission to marry by Jun-su's father, but after a horrible accident, Jang Guk loses the baby. Their mothers who were against the relationship from the beginning, take advantage of the situation and split them up. Jang Guk then leaves Korea to live in the U.S. and changes her name to Jang Dal-rae. Twelve years later, they reunite and get entangled in each other's lives again. The only problem is that Yu Jun-su doesn't know it's her and Jang Guk doesn't want him to know.