Marjorie Bowen 
The Poisoners [EPUB ebook] 

In the year 1676 Madame de Brinvilliers was executed in Paris for the murders of her father, her two brothers and a sister. It was known that she had procured the mysterious poison that she had employed through the agency of one Sainte-Croix, who, in his turn, had received it from an Italian, Exili, whom he had met when both these scoundrels had been imprisoned in the Bastille for minor offences.
This affair caused an extraordinary sensation in Paris, but, with the death of the Marquise de Brinvilliers, it was considered closed. When this female “monster, ” as she was termed, had expiated her crimes, public interest in the matter waned and police investigations into the question of poisons ceased.
Shortly after the execution of Madame de Brinvilliers, however, the priests who were in charge of Notre-Dame, the most fashionable church in Paris, informed the police that “an enormous number” of their penitents, when in the sanctity of the confessional, accused themselves of poisoning their husbands. The active and intelligent Chief of Police, M. de La Reynie, refused to give any importance to this information; he thought that these women were so affected by the Brinvilliers case that they had become hysterical and that these painful derangements were better ignored.