King Rudolph of Rugaria sends his son, Prince Boris, to America to marry into wealth so that the country can recover from its financial difficulties. Rich Mrs. Hanway, eager to have her daughter Althea become a princess, takes her with Boris to Rugaria.
George Crosby, a New York lawyer, with a passion for painting, wearied of his legal duties, sails for Brittany, where he meets Renée Kerouac, a fisher-maiden, and sketches her as a Corregan, a fairy who destroys the men who refuse her love. Hoel Kalloc, her betrothed, becomes jealous, and George marries her, after saving her from Hoel's brutality.
In 64 A.D., Marcus Superbus is Prefect of Rome. When the Emperor Nero decides to renew persecution of the Christians, Marcus opposes him, fearing for the safety of Mercia, the Christian woman whom he loves. Through the machinations of the Empress Poppaea and other women at court, Tigellinus, Nero's agent in the war against the Christians, convinces Nero to have Mercia arrested. Marcus appeals to the emperor for mercy, but is told that she can be saved only by renouncing Christianity. Waiting to enter the arena to be killed, Mercia steadfastly refuses to reject her religion, despite Marcus' pleas. Finally, Marcus is converted by her and they enter the arena to face death together.