City of Light, City of Poison

What made La Reynie effective was not force but patience. He treated the city as a text to be read, and he understood that the most valuable currency in Paris was not money but information. He cultivated informants across every class — servants, priests, apothecaries, the women who sold powders in back rooms — and he wrote everything down. His notebooks, which Tucker leans on heavily, are the record of a mind assembling a picture that no one else could see because no one else was collecting all the pieces in one place.

The break came, as such breaks often do, almost by accident. In 1676 the Marquise de Brinvilliers was arrested after a scandal in which private papers surfaced suggesting she had poisoned her own father and two brothers to secure their inheritances, with the help of her lover. Her trial and public execution were a sensation. But for La Reynie the trial was less an ending than an opening question: if a woman of that rank could quietly murder her family with purchased poison, how many others were doing the same, and where were they all getting the arsenic?

At the center of the tangle sat a woman named Catherine Monvoisin, known to all of Paris as La Voisin. She was a fortune-teller, an abortionist, a dealer in charms and powders, and she was very good at all of it. Fashionable women climbed the stairs to her house to have their palms read and their futures arranged; some left with love potions, some with something darker. When La Reynie's men arrested her in 1679, the door they opened led not to one criminal but to an entire economy of the occult and the lethal.

Under interrogation, La Voisin and her associates described a trade that mingled superstition and pharmacology in ways that horrified the investigators. There were powders of Spanish fly and arsenic, but there were also black masses — obscene rituals performed by renegade priests, most notoriously a defrocked cleric named Étienne Guibourg, over the bodies of women, sometimes involving the sacrifice of infants, all commissioned to bind a lover or curse a rival. Tucker is careful here: some of this testimony came under torture and cannot be taken at face value. But the sheer volume and consistency of it, drawn from many mouths, told La Reynie he was dealing with something real and organized.

The name was Madame de Montespan, the king's official mistress for more than a decade and the mother of several of his children. Witnesses from the poison network claimed she had, over the years, bought love powders to keep the king's affection and, more damningly, that she had participated in black masses and later sought poison to be rid of a younger rival. Whether every detail was true is impossible to know; the testimony came from desperate people facing execution, and torture manufactures the confessions it wants. But the accusations, once made, could not be unmade.

This is where Tucker's story stops being a detective tale and becomes something colder. La Reynie now held knowledge that threatened the emotional and political center of the regime. If Montespan were tried, the king's private life, his children's legitimacy, and the dignity of the crown itself would be dragged through a public court. The lieutenant of police had done exactly what he was appointed to do — follow the crime wherever it went — and doing his job had brought him to a door he was not permitted to open.

Montespan was never charged. She kept her apartments and her pension for years, drifting slowly out of favor by the ordinary means of a younger woman arriving, and died in 1707 without ever answering for what the testimony had claimed. La Reynie stayed at his post until near the end of his long life, expanding the police force he had built, keeping his copied papers, saying nothing. The Sun King's Paris got its lanterns and its order, and it kept its secret in the same stroke.