As Gilles wasted yet more of his fortune and sold more lands, simultaneously committing the litany of alleged crimes described above, he was increasingly a man under scrutiny. Rich in land though he was, Gilles could not sell his property quickly enough to keep pace with his expenditure, and this made him desperate. Having sold the castle of Saint-Etienne-de-Mere-Mortè, he decided that he needed it back in 1440. To do so, Gilles menaced the key-bearer with a battle-axe, dragging him to the castle to open it up, before finally incarcerating him. Unfortunately, the key-bearer, Jean le Ferron, was a priest.
By interrupting le Ferron in the middle of mass and threatening him, Gilles had committed blasphemy and abused both the church’s right of sanctuary and the benefit of the clergy. And he had stolen a castle, to boot. Unfortunately, Jean, Duke of Brittany, looked covetously upon the possessions of Gilles, and had been waiting for an opportunity to take some of his lands at a bargain price. For his actions, the Duke slapped Gilles with a fine of 50, 000 écus, which he knew he could not afford to pay without selling everything besides his castles at Tiffauges and Pouzauges.
Before Gilles could work out how to pay his fine, the Duke of Brittany’s Chancellor, the Bishop of Nantes, secretly published and circulated a writ of defamation in late July 1440, which detailed the profane allegations against Gilles that had been circulating. On September 15, 1440, the Duke of Brittany sent his captain of arms with 30 men to arrest Gilles. Gilles calmly observed the Duke’s men approach from the castle parapets, heard them state their mission, and allowed himself to be arrested without protest for the various allegations, though he had 200 men garrisoned with him at Machecoul.