The story is principally set in and near Paris between 1789 and 1792. Yann Margoza, the protagonist, is a young traveling entertainer with the ability to read minds and throw his voice. When he gets older he finds that he can move objects with his mind (telekinesis). He meets Sido, the unwanted daughter of the cruel and foolish Marquis de Villeduval, and she helps Yann escape from the murderous Count Kalliovski, a menacing nobleman who holds the majority of the French aristocrats in the palm of his hand. He, too, has the power of telekinesis. After being educated in London, Yann returns years later to rescue Sido from the twin perils of the Terror and the Count's evil desire to have her as his bride.