Illegitimate princess Callista trades bridal engagements with her half-sister Elle to claim one billion gold coins and buy the world's only Dawnlight Petal to save her dying mother. In Elle's place, she marries Isvel, the feared Black Dragon of the Abyss—only for Elle and Prince Gareth to steal the petal, leaving her mother to die. Gareth finally realizes he loved the wrong woman and chases after her too late. The supposedly bloodthirsty dragon is in truth gentle and loyal, shielding her again and again. Callista never looks back, falls for him, and becomes his queen as evil gets its due.