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 Eun Seo. However, the other was raised by a single parent and was living in poverty. Her name was Choi Sin Ae. One day Eun Seo has a car accident and by a blood test it is found that Eun Seo and Sin Ae were swapped at birth. Girls were returned to their original places. Eun Seo's brother Yoon Jun Seo is especially confused and saddened by this. Some years later, Choi Eun Seo and Yoon Sin Ae bump into each other at hotel. Eun Seo is a poor worker and Sin Ae is a hotel manager. Meanwhile, Jun Seo 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, Eun Seo. Now all the relationships start to twist around and Eun Seo and Jun Seo's sad love begins.