There were two girls who were born in October. They had same birthday and were raised in the same village and in the same class. One led a happy life with loving parents and a brother. Her name was Yoon Eunseo. However, the other was raised by a single parent and was living in poverty. Her name was Choi Shinae. One day Eunseo has a car accident and by a blood test it is found that Eunseo and Shinae were swapped at birth. Girls were returned to their original places. Eunseo's brother Yoon Joonseo is especially confused and saddened by this. Some years later, Choi Eunseo and Yoon Shinae bump into each other at hotel. Eunseo is a poor worker and Shinae is a hotel manager. Meanwhile, Joonseo has become an artist and has a fiancée. One day he's introduced to his friend's girlfriend, and she was his long-lost sister, Eunseo. Now all the relationships start to twist around and Eunseo and Joonseo's sad love begins.