Mia transmigrates into a book, becoming host of the Heartbind Gu belonging to Uri, the Gu king. To return to the real world, she must stop Uri from placing the Gu on the original female lead. She pretends to grow close to Uri, winning him over. Mia learns a deadly mother Gu resides inside Uri. When the Black Gate opens, Uri takes the backlash to protect her and falls into darkness. Mia makes up her mind to bring this young man back.
