On March 12, 1679, Catherine Monvoisin heard mass at Notre-Dame de Bonne-Nouvelle in Paris and was arrested at the church door. She had been on her way to see a friend, the fortune teller Catherine Trianon. According to what her associates later told investigators, the two women were about to plan a second attempt on the life of Louis XIV, a week after a poisoned petition La Voisin had carried to the court at Saint-Germain failed to reach the king's hands. The plan, as her associates later described it, had been drawn up at Trianon's house with two other poisoners, Bertrand and Romani, the second of them engaged to her daughter, and Trianon had tried to talk her out of it by telling her a bad fortune. At Saint-Germain the crowd of petitioners had been too thick and the king had not taken the paper; back in Paris, La Voisin handed it to her daughter Marguerite, who burned it. Her maid, Margot, told the police that the arrest would be the ruin of people at every level of society. The commissioner, Gabriel Nicolas de La Reynie, took the warning seriously.
La Voisin was, by then, the most famous fortune teller in Paris. Born Catherine Deshayes around 1640, she had learned to read palms as a child, she said, and when her husband, Antoine Monvoisin, a jeweler and silk merchant with a shop on the Pont-Marie, went bankrupt, she supported him, her mother and her children by reading hands and faces. She also worked as a midwife, and that became a business in abortions, then illegal, carried out through a network of women who paid her a share. From her house at Villeneuve-sur-Gravois she saw clients all day and gave parties in her garden at night, with violins. In 1665 or 1666 she was questioned over her divination and defended herself successfully before theologians of the Sorbonne. She owned a robe of crimson velvet embroidered with gold eagles that had cost fifteen hundred livres. She drank heavily, and she kept a string of lovers, among them the executioner André Guillaume, a viscount, an alchemist, an architect and the magician Adam Lesage, who at one point persuaded her to start poisoning her husband before she changed her mind and stopped.
What her clients wanted, she found, came down to three things: someone to love them, someone to die so they could inherit, or a spouse to die so they could marry again. She sold them what they asked for, in stages. First prayers to particular saints, then amulets, then love powders, then black masses said by renegade priests such as Étienne Guibourg, and finally poison, supplied through a circle of dealers that included Trianon. Lesage burned clients' written wishes in balls of wax and later admitted that it had all been a con.
The investigation that swept her up had been building for years. The execution of the Marquise de Brinvilliers in 1676 for poisoning her father and brothers had fixed the idea of noble poisoners in the public mind. In 1677 a fortune teller named Magdelaine de La Grange, arrested for poisoning, said she knew of crimes of great importance. In January 1679 the arrests of two more, Marie Bosse and Marie Vigoreux, showed the police a whole network of women in Paris selling poison. That April the king created a special commission to try the accused, the chambre ardente. Over three years it held 210 sessions at the Arsenal, issued 319 writs of arrest, and sentenced thirty-six people to death.
La Voisin was held at Vincennes and questioned for eleven months. On December 27, 1679, the king ordered that the whole network be rooted out by every means, regardless of rank, sex or age, and her daughter, Guibourg, Lesage, Bertrand, Romani and the rest of her circle were arrested. A warrant permitting torture was issued and, by La Reynie's account, deliberately never used; the fear was that under torture she would name people no one wanted named. Her interrogators, aware that she drank, kept her supplied instead. She admitted in October to selling poison and magical services to several people at court, and named two clients, Marguerite Leféron and Françoise de Dreux. She said Paris was full of this kind of thing. She denied ever meeting Madame de Montespan, the king's mistress. She denied the black masses. She denied burning in her oven the remains of fetuses too large to bury in her garden, which was what Marie Bosse had accused her of. She told her guards that the question she feared most was about her visits to the court.
She was tried from February 17 to 19, 1680, convicted of witchcraft, and sentenced to be burned. The official record says she was tortured afterward until she begged for mercy. La Reynie said she never was. Madame de Sévigné, who saw her shortly before the end, wrote that she moved so freely that it did not seem possible she had been tortured. On February 22 she was taken to the Place de Grève. She pushed the priest away on the way there, and when she had been fastened to the stake she fought to push away the straw piled around her.
The names she had refused to give came out after she was dead. In July and August 1680 her daughter, Marguerite Monvoisin, gave a confession that named her mother's clients, tied Montespan to love powders, to black masses, the first of them said in 1667 in a house on the rue de la Tannerie, and to the plot against the king, and described the poisoned petition. Lesage, promised his freedom by the minister Louvois, confirmed it in September and added that children had been sacrificed at the masses. Françoise Filastre confirmed both. Those accusations came from people bargaining for their lives, some of them after torture, about a woman who was already dead and could not answer them.
They were also the accusations Louis XIV could least afford to hear. He closed the investigation, had the testimony concerning Montespan sealed, and put the remaining prisoners beyond the reach of any court by locking them away on lettres de cachet, without trial, for the rest of their lives. By most accounts he later burned the papers himself. The abortion side of La Voisin's business, which Bosse's accusations concerned, was left the least investigated of all on his orders.
That is where the figures attached to her name come from. Popular accounts put her victims at a thousand, or two thousand five hundred, counting infants from the abortion practice and the alleged sacrifices along with the people her clients poisoned. None of those numbers comes from a count. They come from accusations made by rivals and associates, most of them after her death, to a tribunal that the king then shut down and whose records he destroyed. What the surviving record supports is a long career selling abortions, aphrodisiacs and poison to people who wanted someone gone, and one conviction, for witchcraft, which sent her to the fire.