"Unfinished Story" is a book that was written a long long time ago and has been kept in Misun's grandparents' library for decades. Since Misun loves to read so much, she would usually sneak into the place without them finding her. But one day, Misun gets accidentally locked inside and there she finds an old book written with an ink pen "Unfinished Story." Little did she knew that reading it would bring her somewhere far back into the past where she finds herself inside a body that appears to be her, yet it wasn't her. Instead, a royal princess who is going to get marry to the man of her parent's choice! What will Misun do? It is now up to her to decide the path for the princess and how her story will end. But will it be a happy ending or just another tragic story?