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 Shin-ae. One day Eun-seo has a car accident and by a blood test it is found that Eun-seo and Shin-ae were swapped at birth. Girls were returned to their original places. Eun-seo's brother Yoon Joon-seo is especially confused and saddened by this. Some years later, Choi Eun-seo and Yoon Shin-ae bump into each other at hotel. Eun-seo is a poor worker and Shin-ae is a hotel manager. Meanwhile, Joon-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 Joon-seo's sad love begins.