On his return to Paris the same evening he had reported his discovery at once to the Committee of Public Safety. Billaud-Varennes rubbed his hands gleefully. He was on the scent of a plot. An Englishman? That could be no other than Vaughan, Fox's agent, who was known to have been already two days in Paris. Ah! Robespierre had secret interviews with him, had he? A plot, of course! It was splendid! Nothing could be more opportune!
"Run quickly, and ascertain if the Englishman is still at the American Consulate, while we draw up the warrant of arrest!" was his immediate order.
But at the Consulate the detective was told that Vaughan had just left Paris. Suspecting a trick, he took other means to continue his inquiries, only to find after all that the Englishman had started for Geneva directly after leaving Montmorency.
The members of the Committee were greatly disappointed on learning that the plot must remain unravelled, for how could they prove the interview without witnesses? Coulongeon was the only one who had seen Robespierre speaking with Vaughan, but he was in the pay of the Committee, and no one would believe him. They rested their hopes on the probable return of the Englishman, but they waited to no purpose, and were finally obliged to abandon the attempt.
One evening, however, Coulongeon had brought the Committee an unlooked-for piece of news. Having had a message to take to the prison of La Bourbe, he had found himself in the Acacia courtyard among the prisoners just at their supper-hour. Two female prisoners had attracted his attention. It seemed to him as if it was not the first time he had seen them, and after searching his memory for a moment, he recognised them as the two women who were with Vaughan in the forest of Montmorency before Robespierre arrived on the scene. Yes, he remembered it all now! It was so! There was not the slightest doubt! The gaoler, when questioned, completely confirmed his suspicions. The women did come from Montmorency, where they had been arrested by Robespierre's orders. "Now we have two witnesses!" Billaud-Varennes cried in delight.
"Three!" the agent interjected. "For, now I come to think of it, there was a young man with them."
"He must be found also! Quick to Montmorency, and bring him back with you!"
At Montmorency, after two days of fruitless search, the detective discovered Clarisse's house in the forest. The gardener on being interrogated replied that he was completely ignorant of the whereabouts of Olivier, who had disappeared the very day his mother and his fiancée were arrested.... Perhaps Leonard the locksmith could tell him. Questioned in his turn, Leonard replied evasively. Coulongeon then informed him who he was, and threatened him with the law, so that Leonard ended by owning that the young man had started the same night for Paris. He swore that was all he knew. Coulongeon, pretending to be quite satisfied, thanked him and went away. But returning soon after he adroitly questioned the neighbours on Leonard's connections and acquaintances. The agent learnt that when the locksmith went to Paris he took up his abode in furnished apartments in the Rue de Rocher, kept by a certain widow Beaugrand.
"Now I am on the right track," thought Coulongeon.
Once back in Paris the agent had little difficulty in making the good woman speak. Did the widow Beaugrand know the young man? Pardieu! She knew him too well! He was the daring insulter of Robespierre, the young madman arrested on the Fête of the Supreme Being who was now imprisoned at La Force.