The Sergeant was at first going to kill the Undying Martyr when he pulled himself from the River Tristesse, as no Human could have survived to cross it. However Montaig stayed his hand, after he saw an Aquila hanging from the Martyr's neck. This led the Sergeant to instead deliver the Martyr to Chaplain Malvoisin who would decide his fate. This proved to be a significant decision for the Chapter, as after talking to the Martyr, the Chaplain declared him to be a prophet of the Emperor. This caused the Chapter to listen to his words and with their Chapter Master, Varzival, away campaigning, no one could stop the Angels from falling under the Martyr's sway. He became their spiritual leader and declared the Chapter to be too prideful and vain. The Martyr demanded they destroy everything that tied them to their sinful past and the Great Purge began. Gripped in self-hatred by the Martyr's revelations about their Chapter, Montaig and most of the Angels did as he commanded asked, with only the Librarians refusing to follow his orders. This led them to become targets for the Chapter's wrath and Chaplain Malvoisin led Montaig and a group of Battle Brothers against them. When Malvoisin's group went to attack, however, Chief Librarian Athanazius and the other Librarians, did nothing to defend themselves. Instead Athanazius uttered the Resplendent's battle cry, "We will rise on burning wings". This brought the attacking Battle Brothers to a stand still, especially Montaig who felt his new found self hatred drain away. However, Chaplain Malvoisin, who was the main advocate for the Martyr's changes, yelled out the Penitent's new battle cry, "The Emperor Condemns". This roused the hatred of the attacking Battle Brothers once more and the Angels Penitent were born with the Librarians' deaths. Despite taking part in the Purge, though, Montaig began to doubt the Martyr's words and secretly saved the Lethean Revelation tomb from being destroyed. A decade after that event, Montaig fully renounced what his Chapter had become, but he knew to that publicly would lead to his death.
Instead the Sergeant held on to the belief that the Angels' Chapter Master would return and restore the Angels Resplendent once more. As he waited for that time to come, Montaig read from the secreted away Lethean Revelation to restore his faith in the face of what his Chapter had become. The Sergeant also began to convince himself each day, that he would take a stand against the Chapter, but never did so. However this later led him to defy the Council of Thorns, that now led the Angels, after his mentee-Neophyte Phelion was placed in a cell, for creating art. This was now forbidden due to the Martyr's teachings and Phelion's scrimshaw carvings had caused the Council of Thorns to offer him two punishments for his sins: the Neophyte could take the Path of Chains, which would leave him to become an ankoryte within the Chapter, or tear himself apart by taking the Path of Thorns. When the Council later called for Phelion to choose his fate, Montaig was chosen to escort the Neophyte to their chambers. Before doing so, the Sergeant tried to convince Phelion to take the Path of Chains, but the Neophyte refused to accept the fate that awaited him if he did. He was intent instead on successfully passing through the Path of Thorns, but Montaig told Phelion there was no doubt he would die in the attempt. The Neophyte's predicament weighed heavily upon the Sergeant, as he had known about Phelion's scrimshawing and had tried to prevent others from learning of it. Montaig truly felt, though, the Neophyte had committed no sin in doing so and decided to take a stand against the Chapter, by helping Phelion escape into their Homeworld's wilderness. He explained his reasoning for doing so to Phelion, but to his horror the Neophyte rebuked his efforts. Phelion had become a fervent believer of the Martyr's teachings and this had caused him to confess his vain scrimshawing to the Council of Thorns. The Neophyte then demanded that Montaig confess his sins as well, since he knew Phelion's secret and had done nothing about it. Montaig would not do so, but knew what his fate would be, if Phelion told anyone about his sins. With only one choice left before him, the Sergeant killed Phelion and then began concocting a story of how he was forced to kill the Neophyte after an escape attempt. As he did so, Montaig also promised himself that he would take a stand against the Chapter another day...