By this time the anger and indignation of M. de Lamotte blazed forth. He told Derues that his story was a pack of lies, that he was still master at Buisson-Souef, and not a bottle of wine should leave it. "You are torturing me," he exclaimed, "I know something has happened to my wife and child. I am coming to Paris myself, and if it is as I fear, you shall answer for it with your head!" Derues, undismayed by this outburst, re-asserted his ownership and departed in defiant mood, leaving on the premises a butcher of the neighbourhood to look after his property.
But things were going ill with Derues. M. de Lamotte meant to show fight; he would have powerful friends to back him; class against class, the little grocer would be no match for him. It was immediate possession of Buisson-Souef that Derues wanted, not lawsuits; they were expensive and the results uncertain. He spoke freely to his friends of the difficulties of the situation.
What could he do? The general opinion seemed to be that some fresh news of Mme. de Lamotte—her reappearance, perhaps—would be the only effective settlement of the dispute. He had made Mme. de Lamotte disappear, why should he not make her reappear? He was not the man to stick at trifles. His powers of female impersonation, with which he had amused his good friends at Buisson-Souef, could now be turned to practical account. On March 5 he left Paris again.
On the evening of March 7 a gentleman, M. Desportes of Paris, hired a room at the Hotel Blanc in Lyons. On the following day he went out early in the morning, leaving word that, should a lady whom he was expecting, call to see him, she was to be shown up to his room. The same morning a gentleman, resembling M. Desportes of Paris, bought two lady's dresses at a shop in Lyons.
The same afternoon a lady dressed in black silk, with a hood well drawn over her eyes, called at the office of M. Pourra, a notary.
The latter was not greatly attracted by his visitor, whose nose struck him as large for a woman. She said that she had spent her youth in Lyons, but her accent was distinctly Parisian. The lady gave her name as Madame de Lamotte, and asked for a power of attorney by which she could give her husband the interest due to her on a sum of 30,000 livres, part of the purchase-money of the estate of Buisson-Souef, which she had recently sold. As Mme. de Lamotte represented herself as having been sent to M. Pourra by a respectable merchant for whom he was in the habit of doing business, he agreed to draw up the necessary document, accepting her statement that she and her husband had separate estates. Mme. de Lamotte said that she would not have time to wait until the power of attorney was ready, and therefore asked M. Pourra to send it to the parish priest at Villeneuvele-Roi; this he promised to do. Mme. de-Lamotte had called twice during the day at the Hotel Blanc and asked for M. Desportes of Paris, but he was not at home. While Derues, alias Desportes, alias Mme. de Lamotte, was masquerading in Lyons, events had been moving swiftly and unfavourably in Paris. Sick with misgiving and anxiety, M. de Lamotte had come there to find, if possible, his wife and child. By a strange coincidence he alighted at an inn in the Rue de la Mortellerie, only a few yards from the wine-cellar in which the corpse of his ill-fated wife lay buried. He lost no time in putting his case before the Lieutenant of Police, who placed the affair in the hands of one of the magistrates of the Chatelet, then the criminal court of Paris. At first the magistrate believed that the case was one of fraud and that Mme. de Lamotte and her son were being kept somewhere in concealment by Derues. But as he investigated the circumstances further, the evidence of the illness of the mother and son, the date of the disappearance of Mme. de Lamotte, and her reputed signature to the deed of sale on February 12, led him to suspect that he was dealing with a case of murder.
When Derues returned to Paris from Lyons, on March 11, he found that the police had already visited the house and questioned his wife, and that he himself was under close surveillance. A day or two later the advocate, Duclos, revealed to the magistrate the fictitious character of the loan of 100,000 livres, which Derues alleged that he had paid to Mme. de Lamotte as the price of Buisson-Souef. When the new power of attorney purporting to be signed by Mme. de Lamotte arrived from Lyons, and the signature was compared with that on the deed of sale of Buisson-Souef to Derues, both were pronounced to be forgeries. Derues was arrested and lodged in the Prison of For l'Eveque.
The approach of danger had not dashed the spirits of the little man, nor was he without partisans in Paris. Opinion in the city was divided as to the truth of his account of Mme. de Lamotte's elopement. The nobility were on the side of the injured de Lamotte, but the bourgeoisie accepted the grocer's story and made merry over the deceived husband. Interrogated, however, by the magistrate of the Chatelet, Derues' position became more difficult. Under the stress of close questioning the flimsy fabric of his financial statements fell to pieces like a house of cards. He had to admit that he had never paid Mme. de Lamotte 100,000 livres; he had paid her only 25,000 livres in gold; further pressed he said that the 25,000 livres had been made up partly in gold, partly in bills; but where the gold had come from, or on whom he had drawn the bills, he could not explain. Still his position was not desperate; and he knew it. In the absence of Mme. de Lamotte he could not be charged with fraud or forgery; and until her body was discovered, it would be impossible to charge him with murder.
A month passed; Mme. Derues, who had made a belated attempt to follow her husband's example by impersonating Mme. de Lamotte in Paris, had been arrested and imprisoned in the Grand Chatelet; when, on April 18, information was received by the authorities which determined them to explore the wine-cellar in the Rue de la Mortellerie. Whether the woman who had let the cellar to Derues, or the creditor who had met him taking his cask of wine there, had informed the investigating magistrate, seems uncertain. In any case, the corpse of the unhappy lady was soon brought to light and Derues confronted with it. At first he said that he failed to recognise it as the remains of Mme. de Lamotte, but he soon abandoned that rather impossible attitude. He admitted that he had given some harmless medicine to Mme. de Lamotte during her illness, and then, to his horror, one morning had awakened to find her dead. A fear lest her husband would accuse him of having caused her death had led him to conceal the body, and also that of her son who, he now confessed, had died and been buried by him at Versailles. On April 23 the body of the young de Lamotte was exhumed. Both bodies were examined by doctors, and they declared themselves satisfied that mother and son had died "from a bitter and corrosive poison administered in some kind of drink." What the poison was they did not venture to state, but one of their number, in the light of subsequent investigation, arrived at the conclusion that Derues had used in both cases corrosive sublimate. How or where he had obtained the poison was never discovered.
Justice moved swiftly in Paris in those days. The preliminary investigation in Derues' case was ended on April 28. Two days later his trial commenced before the tribunal of the Chatelet.