Elodie, an orphan, is forced to take her stepsister Nina's place as a bride sacrifice to the last dragon on Deep-Sea Dragon Isle. On the isle, she finds all previous brides dead. She tries to flee but is recaptured. She saves an injured man named Karen and discovers she is immune to dragon-fire. Selene, a jealous witch, exploits Elodie's worry for her brother, setting traps to drive her away and create conflict with the dragon. Elodie returns home, only to see her stepmother's cruelty—she plans to use Elodie as a pawn. Selene then fabricates betrayal to enrage Karen. The dragon descends upon the mortal realm for vengeance. Karen meets Elodie's brother, learns the truth, rescues the siblings, and brings them back to Dragon Isle. Selene's conspiracy is exposed—she colluded with the royal court to besiege the isle. Elodie awakens her curse-breaking power to fight the witch. Selene is defeated. The royal army halts. Karen breaks his curse and regains human form. Elodie frees herself from her family, protects her brother, and stays with Karen on Dragon Isle. Their love ends three hundred years of lonely fate.