Na-ra hopes to marry Seung-woo, but after he returns from a business trip, he unexpectedly breaks up with her on their anniversary, telling her that not only did he have an affair, but he fell in love with the other woman, a cosmetics manager named Cha Mi-rae.

To drown her sorrows, Na-ra drinks a large amount of alcohol and unknowingly drops the ring Seung-woo once gave her into a shot glass of soju.

Later, Na-ra decides to confront the woman who stole her boyfriend, but while at Mi-rae's cosmetics company, a job ad catches her eye.

With nothing to lose, Na-ra fakes being her 20-year-old sister Na-kyung, a high school graduate, and starts working as a sales clerk at the company.

But what she doesn't know is that In-jae is actually the son of the company's vice president who was forced by his mother to learn the ropes by starting from the bottom.