The escapades of the Marquise de Brinvilliers, who spends her nights gambling, are very expensive.  She has hardly any trouble convincing her lover, Jean-Baptiste Gudin de Sainte-Croix, to furnish her with some “succession powder”, as poison will soon be called – by a witty euphemism, which is quite in the spirit of the times.  We do not know exactly what was contained in the terrible mixtures of Sainte-Croix.  Probably poisonous herbs, viper and toad powders, Cyprus vitriol [sulphuric acid] and arsenic.  Anyway, the Marquise, having metamorphosed herself into a benevolent nurse, to experiment on the poor inmates of Hotel-Dieu, sends her spouse into a better world in 1666, then her two brothers in 1670, so as to inherit from them.  For good measure, she also tries to assassinate her sister, Therese d’Aubray, a bigot, whose remonstrances exasperate her, and even her own daughter, of whom she will say, to justify herself, that she was “stupid”.  It is true that there is nothing to stop the lady poisoner from pursuing her career.  Medicine is, at this time, incapable of detecting the traces of poison in internal organs, and although the surgeons have some doubts about the origin of her second brother’s death, not the slightest breath of suspicion touches the Marquise.  Catastrophe strikes at the death, this one natural, of her lover, on 31 July 1672.


At Sainte-Croix’ home, the police find a box containing his more than compromising correspondance with his mistress.  Knowing herself to be lost, the Marquise de Brinvilliers flees to England, then to the Netherlands, and finally to a convent near Liege, from whence she is brought back to Paris manu militari on 26 April 1676 by the lieutenant du chevalier du guet, Francois Desgrez.

The Marquise de Brinvilliers.

Her trial is astonishing.  With a brazenness which, however, is not enough to shake her judges, she starts by denying everything.  Then, under the influence of an eminent theologian called to assist her, Abbot Edmond Pirot, she confesses all her crimes and prepares for death with a contrition, a dignity and a courage which impresses the most hardened hearts.  And on 17 July, after having stoically suffered the Ordinary and Extraordinary Questions (interrogation with tortures in presence of the judge) she is led on a tumbril to the Place de Greve, where she is beheaded.  After which, her body is carried to the stake and her ashes scattered.  Madame de Sevigne, who saw the sinister cortege pass by from the window of a house built on the Notre-Dame Bridge, does not deprive herself of the pleasure of making a witty remark in the letter which, that same evening, she writes to her daughter:

“At last it is done, the Brinvilliers is in the air.  Her poor body was thrown, after execution, into a very big fire, and the ashes to the wind, so that we shall breathe her, and by communication with some little minds, we shall catch some poisoning humour which shall astonish us.”

In her happy unconcern, Mme de Sevigne cannot, of course, guess that she is pronouncing prophetic words there.  This aristocratic gossip-monger is, however, well enough informed to know that, on the very day of her execution, the Marquise de Brinvilliers had a private conversation with the procureur general du parlement de Paris, Achille de Harlay.  She writes:

“The subject of this conversation is not yet known.”

But its content is sufficiently important for Colbert, once told about it, to inform Harlay that Louis XIV is asking him to come to relate to him “all that is happening in the follow-up to the case of Lady de Brinvilliers”.

What did Harlay learn?  Today, we are reduced to conjectures.  It is not difficult, however, to imagine that the Marquise knew more than she had wanted to say at her trial about the world of poisoners, and that, as Arlette Lebigre observes, she had perhaps tried in extremis to warn “that danger still prowled and that no-one was safe from it”.  The events which follow will support this hypothesis…


While the Marquise de Brinvilliers is mounting the scaffold, another case, sadly banal in appearance, is occupying the lieutenant general de police, Gabriel Nicolas de La Reynie.  He is preparing the trial of a certain Madeleine Gueniveau, known as Mademoiselle de la Grange, who is accused of having poisoned her lover, Maitre Faurie, an elderly and very rich lawyer whom she despairs of marrying.  At the man of Law’s sudden death, she immediately takes possession of his goods, to the disagreeable surprise of the dead man’s nephews.  Madeleine then exhibits a marriage certificate established by a certain Abbot Nail and a contract established before the marriage in front of a notary, instituting her as the only heir.  The nephews, smelling fraud, have filed a complaint, and the two accomplices have rapidly found themselves in prison.  During the investigation, Me Faurie’s domestics are not slow in voicing their suspicions, to such a degree that an inculpation for poisoning is added to those of supposition of marriage and misappropriation of succession.  Playing her last card, in January 1677, Mlle de la Grange asks to speak to Louvois, himself, to make revelations to him which could, perhaps, merit her being given clemency by her judges.  These revelations are serious enough for the great Minister, convinced that “we need to be very careful about the business of which she spoke”, to entrust the case to La Reynie with this precision:

“His Majesty has commanded me to tell you that he expects you to follow this case with application and that you will forget nothing in clarifying it.”

This time, it is not a simple family problem about which Mlle de la Grange has talked to Louvois, but a plot against the King’s person.  True or false, the lady poisoner’s confession is reinforced in September by a strange letter, with no signature and without the name of the addressee, which finds its way to Colbert who immediately transmits it to La Reynie.  In it, these two sibylline sentences are noteworthy:

“This white powder, that you want to put on the towel of you know who, can it be recognized as having the effect to which it is destined?  I leave you to judge what would happen about it!

Further on, two other sentences leave hardly any doubt about the identity of “you know who”:

“I fear extremely that our letters might be seen and that I am believed to be guilty, even though I am very innocent [in the feminine].  For in all the other crimes one must be an accomplice to be punished, but for this one, one only has to have known of it.”

Only the crime of lese-majeste automatically results in the death sentence of whomever had knowledge of it without immediately telling the authorities.

To be continued.