This historical novel of pre-Revolutionary France is romantic in the 19th century tradition, but with a strong mystical element added. Gabrielle de Ferardet and her brother, Perelot, have been left a legacy by an English cousin. They are as different as brother and sister can be. The Protestant Gabrielle is beautiful, headstrong, and moves in court circles. Perelot is a fanatical Catholic who hoped to join the brotherhood of monks that raised him, and is gauche, timid, and credulous when they send him into the world. The English Earl of Karsdale, agent to the British Prime Minister at the court of France, has been made guardian of his young cousins through the terms of his mother's will. He and Gabrielle fall deeply in love despite the fact that when they meet he is not free to marry. All these people know the mysterious Comte de St. Germain in different ways. To Gabrielle he is the godlike mentor and master that she has known since childhood. To Perelot, he is the heretic and necromancer who must be killed for the glory of the church. To Anthony Karsdale he is the urbane master spy who knows the secrets of all the courts of Europe. Finally he is revealed as a man with genuine supernatural powers: able to raise the dead, duplicate jewels, and save Anthony's life by miraculously appearing on a mountain ledge in India. Even when Perelot, who has become associated with the revolutionary activities of the peasants under the evil influence of Robespierre, kills Anthony as he and Gabrielle are on the point of fleeing to England, the Comte appears in a deus ex machina fashion and revives him from the dead.