Seo Joohyun had an accident, making her lose her memory. Although she is happy as it is now, she wants her old memory and her old life back. She was told everything she needed to know about her old life from her friends and family ,and it helped her gain some of her memories. But the returned memories she has now is not enough for her.

Then Seo Joohyun met Kyuhyun.          She felt a sense of familiarity.     Then Kyuhyun started talking about a promise he made to somebody but Joohyun didn't care.  All she cared about was that her heart beats abnormally fast when he's around, that she found herself falling for him. It didn't make sense. Everything did not make any sense. She's too in love for aything to make sense.