Go Eun Sung (Han Hyo Joo) has always had an easy life. The daughter of a wealthy, adoring father, she is encouraged to pursue her dreams and goes abroad to study. The only cloud on her horizon is the fact that her much-loved little brother is autistic. But in a single night she loses her entire world.
When her father suddenly dies under mysterious circumstances, the family discovers that his company has crashed and he left behind a huge number of debts. Her stepmother promptly throws her and her brother out of the house in favor of her own daughter, Seung Mi (Moon Chae Won).
Homeless and penniless, Eun Sung takes a job as a waitress at a night club to support herself and her brother, only to have her brother Eun-woo disappear one day. Eun Sung has hit rock bottom. Her fortunes turn, however, when she takes in an amnesiac old woman she finds at the bottom of some stairs after a fall. When the old woman recovers her memory, she turns out to be Jang Sook Ja, the wealthy CEO of a large food company.
Sook Ja takes Eun Sung in and gives her a job at her company, where she clashes constantly with Sun Woo Hwan (Lee Seung Ki), Sook Ja's spoiled grandson (and heir to the company). Eun Sung's sunny disposition and hardworking principles quickly win everyone over, however, and even begin to thaw the heart of selfish Hwan. What Eun Sung doesn't know is that her stepsister Seung Mi and Hwan are childhood friends, and that her evil stepmother is determined to have Seung Mi marry Hwan...
Han Hyo Joo as Go Eun Sung
Lee Seung Gi as Sun Woo Hwan (Eun Sung's enemy & boyfriend)
Bae Soo Bin as Park Jun Se (Eun Sung's friend)
Moon Chae Won as Yoo Seung Mi (Eun Sung's step-sister)
Kim Mi Sook as Baek Sung Hee (Eun Sung's wicked step-mother)
Min Young Won as Lee Hye Ri (Eun Sung's close friend)
Yun Joon Suk as Go Eun Woo (Eun Sung's lovely brother)
Jung Suk Won as Jin Young Suk (Woo Hwan's friend)
Han Ye Won as Sun Woo Jung (Woo Hwan's sister)
Ban Hyo Jung as Jang Sook Ja (Woo Hwan's grandma)