|Nancy Guild||Marie Antoinette/Lorenza|
|Frank Latimore||Gilbert de Rezel|
|Margot Grahame||Mme. du Barry|
|Stephen Bekassy||Viscount de Montagne|
|Berry Kroeger||Alexandre Dumas Sr.|
|Raymond Burr||Alexandre Dumas Jr.|
|Charles Goldner||Dr. Franz Anton Mesmer|
Joseph Balsamo, a poor French gypsy with a tragic past, is taken under the wing of Dr. Mesmer, who teaches him the secrets of hypnosis. While Balsamo promises the doctor that he will use the power only to help others, he instead abuses his gift in order to steal money and forge himself a powerful reputation. Using his newfound wealth and power, he hatches a devious plan to replace French queen Marie Antoinette with a young woman, Lorenza.