The heroine Chun Hae-joo (Han Ji-hye) begins life in utter poverty. But despite being burdened with the secret past of her parents, she navigates treacherous waters and overcomes obstacles to achieve her dreams. Her childhood sweetheart Park Chang-hui (Jae Hee), son of the butler to a company chairman, also rises above his humble beginnings to become a successful prosecutor. Bright and playful Kang San (Kim Jaewon), the rival boss's privileged grandson, returns to South Korea after years abroad to find that he still carries a torch for Hae-joo. The story starts with the murder of a scientist, Yoon Hak-su. When Hak-su received a phone call, his family is scared and worried. Wealthy company chairman, Jang Do-hyeon, is revealed to be the murderer of Hak-su. He being the superior of Yoon Hak-su wears a mask of grief and takes part in the memorial service, only to take Hak-su's wife, Lee Geum-hee, as his own wife. Her two year old daughter, Yoon Yu-jin, is robbed from her and given away to Chun Hong-cheol, an unemployed and debt-stricken military junior of Park Gi-cheol, butler to Jang Do-hyeon. Even though Do-hyeon orders for Geum Hee's two year old daughter, Yu-jin, to be killed, his butler Park Gi-cheol, is unable to do so because of his conscience. The story moves forward and we see a 13 year old Hae-joo, daughter of the late Yoon Hak-su, living with a family that has a doting foster father Chun Hong-cheol, and an ill-mannered and complaining mother, as she believes Hae-ju to be the husband's illegitimate daughter. Park Chang-hui, the butler's 14 year old son, who is ill-treated by the owner's son, Ill Mun, has his own share of grief. Also there is Kang San, a charming, carefree and cheerful heir of the rival group of Jang Do-hyeon, Haepung Shipping Group. He is the heir to his grandfather's business as his parents are dead. They all meet under one roof at the local school in Ulsan, where Kang San, Chang-hui and Ill Mun attend the same class. Due to their similar situations filled with sadness, Chang-hui and Hae-ju start liking each other. However Kang San starts falling for Hae-ju because of her welding ability and cheerful, positive personality. Due to some tense events, Jang Do-hyeon starts to suspect that his wife's daughter was not killed by the butler 11 years ago and might turn out to be Hae-ju now. So, he orders the butler to solve the problem. Chang-hui's father, the butler, kills Hae-ju's foster father instead when Chun Hong-cheol puts himself between his daughter and the butler's stolen vehicle. Jang Do-hyeon takes over Haepung Shipping Group through deceit and Kang San's grandfather is jailed unfairly. Kang San moves to America for further studies. Hae-ju's family also moves away from Ulsan to Geoje. The story takes a leap in time, 15 years later we see Hae-ju and Park Chang-hui as adults dating. Jang Do-hyeon starts showering respect and praises toward Chang-hui as he is now a Public Prosecutor, a strict one, in hopes that he will protect his company, CheonJi Group. Chang-hui's father, the often abused butler, dreams that one day his son will become the son-in-law of Jang Do-hyeon by marrying Jang Do-hyeon's daughter, In Hwa. He is seen to be playing matchmaker too. Jang Do-hyeon's company bags a contract with an American company which sends their Ship Inspector, Ryan Kang, to oversee the billions of Won project. He turns out to be Kang San who has a big idea for Jang Do-hyeon. He and Hae-ju met at a night club and when she attends an interview for CheonJi Group. She and San work together after he reveals himself. They work together to build a new Azimuth Thruster, so that San can take his Grandfather's company back. But all their efforts are thwarted by Jang Do-hyeon. Meanwhile San loses his job, gets stabbed, and loses his grandfather, while Hae-joo struggles with her family poverty and her growing feelings towards Kang San. Chang-hui under great humiliations and blackmailing from his father marries Jang Do-hyeon's daughter, In Hwa, who is in turn in love with Kang San. Chang-hui starts to play with Jang's daughter to get back at her father. He also learns that his father was behind Hae-ju's foster father's death. After losing his only support, his grandfather, Kang San starts living on the streets and working at a construction site. From great provocation and support from Hae-ju, he moves into her house and starts anew. He also starts uncovering Hae-ju's father's death facts and finds out about her birth mother. After several attempts at uncovering Jang Do-hyeon's deceit by taking his wife's and Hae-ju's uncle's help, they succeed in getting evidence against Jang Do-hyeon. Between this, Chang-hui takes the seat of CheonJi Group and starts sinking low. It is revealed that Jang Do-hyeon is the murderer of Yoon Hak-su, and also that he is Hae-ju's biological father. Because of this revelation, Hae-ju rejects Kang San's marriage proposal, which he does after getting the patent rights registered for their invention. Later, however they both kiss and make up. At the end, we see Chang-hui living with his father at a village while his wife, In Hwa, visits him to say that she loves him. Hae-ju and Kang San leave in their drillship to drill oil in the Pacific whilst he dons her finger with a huge diamond. Jang Do-hyeon, the cause of so much heartbreak, kills himself.
