The story begins with the main character, Cardia, isolated and alone in a mansion on the outskirts of a 19th-century steampunk version of London. A victim of a mysterious affliction that makes her blood a virulent poison and her touch instantly lethal, Cardia is shunned as a monster.

Through a number of events both grand and seemingly insignificant, Cardia is pursued by the Royal Guard, kidnapped by the gentleman thief Arsène Lupin, and joined by a myriad of other handsome figures out of the best of western literature. With her new-found friends (and suitors) Cardia ventures out in the world to unravel the mysteries surrounding her very existence.