Yoon Joon-suh (Song Seung Heon) and Yoon Eun-suh (Song Hye Gyo) grew up as siblings but Eun-suh was in fact from a different family as there was a mixed up at the hospital where she was borned.The switch came to light when Eun-suh was involved in a car accident and it was discovered that her blood type was different from her parents. Eun-suh's life took a complete turn when the 2 girls were returned to their respective families. Soon after, the Yoon family left for the States and Eun-suh was left living in sordid condition with her real family in Korea. Years after, Joon-suh returned to Korea and by chance the two former siblings were reunited.