BLACK MAGIC

Alexandre Dumas, Sr. tells his son Alexandre Dumas, Jr. the story of Joseph Balsamo, also known as Cagliostro. Through flashbacks, we learn that Balsamo was a French Romani boy who endured much hardship. He was tortured under the command of Viscount de Montaigne and his parents were ordered to hang. He was rescued by some Roma people led by Gitano and swears revenge on de Montaigne.

Some years later, he learns the secrets of hypnosis from Dr. Mesmer (Charles Goldner). Ignoring the doctor's advice that he use his powers for healing, he exploits his new talent to the full, gaining wealth and prestige. After changing his name to Count Cagliostro, he becomes famous throughout Europe. Things begin to go downhill when he enters a plot to substitute a young girl called Lorenza for Queen Marie Antoinette along with gypsies Gitano and Zoraida. The plot is organized by de Montaigne in association with Madame du Barry. They plan for Lorenza to impersonate the Queen and buy a frivolous necklace for a large sum of money.

Zoraida becomes jealous of Lorenza, who has fallen under Cagliostro's power, forgetting her true love, Gilbert. Gilbert runs away with Lorenza. Cagliostro recaptures her and marries her, hypnotised. King Louis XV dies and Marie Antoinette becomes queen. She orders Cagliostro to leave the country. Cagliostro gets Lorenza to impersonate the Queen and pretend to be in love with de Montaigne. He buys the necklace and the Queen's reputation is damaged (echoing the real-life Affair of the Diamond Necklace).

Zoraida brings Lorenza to Marie Antoinette and reveals Cagliostro's plot. Lorenza agrees to testify against Cagliostro, but at the trial, Cagliostro hypnotizes her into stating that she knows nothing. Cagliostro hypnotizes Gilbert into testifying against the queen. However, Dr. Mesmer then uses the necklace to hypnotize Cagliostro into confessing. Cagliostro awakens from his trance and escapes with the hypnotized Lorenza. Gilbert pursues them and kills Cagliostro in a sword fight.

Cagliostro is hypnotized into confessing his crimes and is killed in a sword fight with Gilbert as he tries to escape with Lorenza.

The film concludes with poetic justice: Cagliostro, who wielded hypnotism for manipulation and self-gain, is ultimately undone by the very power he misused. Dr. Mesmer's intervention restores agency to his victims and exposes Cagliostro's schemes, while Gilbert's final confrontation brings closure to the cycles of revenge and deception.