Im Yoona once was a young girl who had a terrible past when she was younger. Living in the city with her little brother, Taemin, and an old friend, Minho, she goes to school for the first time. She meets new amazing friends, but then also meets Donghae. She quickly finds out who Donghae really is, and decides to hide away from him and avoid him because of her memories about his father. But... how is she able to hide if Donghae fell in love with her?

Lee Donghae is a very wealthy boy who has a wealthy background. He is the son of Mr. Lee, who used to keep Yoona and Taemin as slaves when they were younger. However, Donghae doesn't know this. He falls in love with the innocent girl. Will he realize what Yoona is running from? Or will he keep finding her and ignore the fact that she's terrified of him?

Choi Minho is Yoona's best friend. They grew up at a small cottage together-- Minho's mother taking care of the three. Minho always admired Yoona, and had a certain feeling for her. It was like a brotherly affection. Though, many people mistaken this feeling for Minho loving Yoona, even know Minho knows by heart that he only loves Yoona like a brother. Will he eventually fall in love with Yoona?

Kwon Yuri is Donghae's-for-now-fiance. She is Yoona's best friend and is a girl who has a huge crush on Minho. She goes crazy around Minho, such as hugging him and shouting his name aloud. Although she doesn't know that Minho doesn't like her, Minho tries to give hints about him not liking Yuri at all. However, Yuri's determined to make Minho hers. She has no interest in her fiance at all, which helps her pay more focus on Minho. Will the crazy girl eventually capture Minho's heart?

Lee Taemin is Yoona's brother. Actually, he is her step brother. Though, they consider each other as brothers and sisters instead of step brother and step sisters. He's a very childish and adorable young man, but sometimes he can go overboard. If no one's smiling or laughing, then Taemin comes in to bring smiles for everyone! But when he meets Sulli... he falls in love. However, Sulli likes mature man because of her own reason. So when Taemin starts to change, how will he affect everyone?

Choi Jinri, otherwise known as Sulli, is actually a very cheerful and bubbly girl! However, at school and home, she acts very mature and puts on a strict and straight face. Knowing that Taemin loves her, she's happy and glad. Though, she does not want to fall in love with Taemin because her family would certainly forbid it and does not want Taemin to know that her family works with Donghae's family. (She knows about Taemin's past and feels guilty.) Will she really let her family get in the way, or will she follow her heart?