Just as the three had determined to penetrate into the Cevennes, they were denounced by some peasants before a Swiss officer named Muller, who was in command of a detachment of troops in the village of Riviere.

Muller instantly mounted his horse, and guided by the informers made his way into the little wood in which the Camisards had taken refuge, and fell upon them quite unexpectedly.
Boyer was killed in trying to escape; Castanet was taken and brought to the nearest prison, where he was joined the next day by Valette, who had also been betrayed by some peasants whom he had asked for assistance.
The first punishment inflicted on Castanet was, that he was compelled to carry in his hand the head of Boyer all the way from La Goree to Montpellier.

He protested vehemently at first, but in vain: it was fastened to his wrist by the hair; whereupon he kissed it on both cheeks, and went through the ordeal as if it were a religious act, addressing words of prayer to the head as he might have done to a relic of a martyr.
Arrived at Montpellier, Castanet was examined, and at first persisted in saying that he had only returned from exile because he had not the wherewithal to live abroad.

But when put to the torture he was made to endure such agony that, despite his courage and constancy, he confessed that he had formed a plan to introduce a band of Huguenot soldiers with their officers into the Cevennes by way of Dauphine or by water, and while waiting for their arrival he had sent on emissaries in advance to rouse the people to revolt; that he himself had also shared in this work; that Catinat was at the moment in Languedoc or Vivarais engaged in the same task, and provided with a considerable sum of money sent him by foreigners for distribution, and that several persons of still greater importance would soon cross the frontier and join him.
Castanet was condemned to be broken on the wheel.

As he was about to be led to execution, Abbe Tremondy, the cure of Notre-Dame, and Abbe Plomet, canon of the cathedral, came to his cell to make a last effort to convert him, but he refused to speak.