Lee Se-na is the only daughter from a wealthy background. Because of her pampered upbringing, she believes that she can get anything she wants if she sets her heart to it. She meets Han Seung-Woo, a self-made diplomat, who is not-so-secretly in love with his childhood friend Yoon-su, currently in Japan with her fiance, Seung-Woo's colleague Jin-Hui. Se-na instantly falls in love with Seung-Woo, who asks her what she thinks the meaning of marriage is. In their subsequent marriage, their values are questioned as Se-na's complete trust in Seung-Woo shatters with the realization of Yoon-su's and Seung-Woo's relationship, and Seung-Woo's happiness in marriage shatters with Se-na's deepening mistrust and her own relationship with Jin-Hui.

Song-yi is a girl with a pure heart with a bad temper. She was tricked and humiliated by her "best friend" Hee-won as a child. From then on, Hee-won has always been the princess and successful while everyone mistook Song-yi as the evil child. When Song-yi did not have a job, Hee-won introduced her to the amusement park that she is in charge of. There she found her childhood friend and ex-crush Hyun-sung, who Hee-won has "stole" when they were kids. From then on, Hee-won tried to humiliate Song-yi many times, framing her in many situations that Hee-won has created herself. To get back at Hee-won, she decided to break the train that the park was launching so that Hee-won would be blamed. Little did she know that she caused more damage and that the train caught on fire. What was worse was that the son of the president of the park was in the train. Ridden with guitl, Song-yi risks her own life to save the life of Seung-joon. Seung-joon fell in love with Song-yi for her brave spirit and charming attitude, but what will happen to their relationship when Hee-won exposes to the world of what she has done?