The Affair of the Poisons by Anne Somerset

There was never a scandal in France to equal the affair of poisons, which appalled and fascinated the court of Louis XIV for several years. Like a lethal version of the Profumo scandal, wild rumours swept through society as prominent people were implicated, the circle widening to include the most unlikely suspects. As a wit remarked of one pious lady hauled in for questioning, "She has never poisoned anyone, unless it's with her breath."

The hysteria began with the trial of the Marquise of Brinvilliers in 1676. She had conspired with her lover to poison her father and two brothers in order to enrich herself. Mme de Sevigné, after describing how the marquise was beheaded, her body thrown on a fire and the ashes to the wind, added that now that "we will be inhaling her", perhaps "we will be taken by some kind of mood for poisoning which will surprise us all".

The person who feared most the "mood for poisoning" was the king. His chief of police, Nicolas de La Reynie, was ordered to investigate links between the aristocracy and the Paris underworld of poisoners, witches, fortune-tellers and charlatans. La Reynie, horrified at this "impenetrable darkness", brought an inquisitorial zeal to the task. To shield the aristocracy from public gaze, a closed court was set up, the Chambre Ardente (burning court) to judge cases of poisoning and witchcraft.

The Chambre Ardente burned, beheaded, hanged, strangled and broke on the wheel 34 people - none an aristocrat. An early execution was that of "La Voisin", a witch and purveyor of love potions to the aristocracy. One of her clients had been Athénais de Montespan, the king's mistress, who had bought aphrodisiacs to slip into his drink.

Soon, scurrilous tales emanated from the prisoners of black masses performed over naked women and sacrificed babies. The alleged involvement of Mme de Montespan was suppressed, even from the Chambre Ardente, by orders of the king, for fear it would be all over Paris. Was Montespan guilty? She could have been the victim of a power struggle between the minister of war, Louvois, and Colbert, the king's controller of finance. Some of the accused were friends of Colbert (his daughter was married to Montespan's niece), but none of Louvois's friends was implicated. Louvois was also aware that Maintenon was in the ascendant, and it was to her advantage for the woman who had held such sway over Louis to be discredited.

In her excellently-researched book, Anne Somerset leaves the reader to judge from the evidence, though she does conclude that "the king had sought to cleanse the realm of poisoners, but in reality it was his mind that had been poisoned". He could see a connection between the disorderly sex lives of the accused and their alleged crimes. Louis, who had been enthusiastically adulterous, retreated to the arms of his wife and, after her death, to a morganatic marriage with the religious Mme de Maintenon. Versailles lost its glitter, and became a thoroughly boring place.

Clare Colvin's novel 'The Mirror Makers', set in the court of Louis XIV, is published by Hutchinson.