As the lieutenant had not drunk enough to be upset by it, he soon forgot this incident and the suspicions that had been aroused at the moment in his mind.  Sainte-Croix and the marquise perceived that they had made a false step, and at the risk of involving several people in their plan for vengeance, they decided on the employment of other means.  Three months passed without any favourable occasion presenting itself; at last, on one of the early days of April 1670, the lieutenant took his brother to his country place, Villequoy, in Beauce, to spend the Easter vacation.  Lachaussee was with his master, and received his instructions at the moment of departure.

The day after they arrived in the country there was a pigeon-pie for dinner:  seven persons who had eaten it felt indisposed after the meal, and the three who had not taken it were perfectly well.  Those on whom the poisonous substance had chiefly acted were the lieutenant, the councillor, and the commandant of the watch.  He may have eaten more, or possibly the poison he had tasted on the former occasion helped, but at any rate the lieutenant was the first to be attacked with vomiting two hours later, the councillor showed the same symptoms; the commandant and the others were a prey for several hours to frightful internal pains; but from the beginning their condition was not nearly so grave as that of the two brothers.  This time again, as usual, the help of doctors was useless.  On the 12th of April, five days after they had been poisoned, the lieutenant and his brother returned to Paris so changed that anyone would have thought they had both suffered a long and cruel illness.  Madame de Brinvilliers was in the country at the time, and did not come back during the whole time that her brothers were ill.  From the very first consultation in the lieutenant’s case the doctors entertained no hope.  The symptoms were the same as those to which his father had succumbed, and they supposed it was an unknown disease in the family.  They gave up all hope of recovery.  Indeed, his state grew worse and worse; he felt an unconquerable aversion for every kind of food, and the vomiting was incessant.  The last three days of his life he complained that a fire was burning in his breast, and the flames that burned within seemed to blaze forth at his eyes, the only part of his body that appeared to live, so like a corpse was all the rest of him.  On the 17th of June 1670 he died:  the poison had taken seventy-two days to complete its work.  Suspicion began to dawn:  the lieutenant’s body was opened, and a formal report was drawn up.  The operation was performed in the presence of the surgeons Dupre and Durant, and Gavart, the apothecary, by M. Bachot, the brothers’ private physician.  They found the stomach and duodenum to be black and falling to pieces, the liver burnt and gangrened.  They said that this state of things must have been produced by poison, but as the presence of certain bodily humours sometimes produces similar appearances, they durst not declare that the lieutenant’s death could not have come about by natural causes, and he was buried without further inquiry.