Ho Goo has a twin sister Ho Gyeong. He has tried to pass the civil service examination, but has failed for 7 years. He also has never dated in his life. One day, he meets Do Hee. She was the most popular girl back in his high school days. She is a member of the national swimming team and has a burning desire to win. She also talks like one of the guys. They spend the night together, but the next morning he finds a baby next next to him and Do Hee is gone. After Ho Goo meets Do Hee again, he becomes involved in a complicated romantic relationship and a dangerous friendship.