The Shriven - Greyshields' Rebellion: At an unknown point during the Indomitus Crusade, a Torchbearer fleet was sent out from the crusade with a complement of two Greyshield Primaris Space Marines companies and detachments of Adeptus Custodes and Sisters of Silence commanded by Captain Gerion, Shield-Captain Tyvar and Knight-Centura Dessima, respectively.The Torchbearers' goal was to reach the Brazen Drakes' homeworld of Khassedur and convince the Brazen Drakes' Chapter Master to accept the Primaris Marine reinforcements and the gift of Belisarius Cawl's Primaris upgrade technology.After long solar months of toil and trial, blazing battlefields and ferocious Warp Storms, the fleet arrived at its destination and discovered the planet had been ravaged by war -- and the Brazen Drakes had already been damned as Hereticus Diabolus Extremis by an Inquisitor of the Ordo Hereticus.Immediately upon learning the news of the Brazen Drakes' decision to turn Renegade, Shield-Captain Tyvar ordered that the Greyshield Primaris Marines who were intended to join the Brazen Drakes be designated as Traitors and captured.Shocked by what he perceived as the sudden and unexpected betrayal of the Custodians when the Primaris Marines had as yet done nothing wrong, Captain Gerion tried to argue in defence of his brothers, who had fought faithfully for the Emperor up to that point.But Tyvar rejected this appeal, believing that the taint already present in the Brazen Drakes' gene-seed was now obviously present in their Primaris brethren. Instead, the Custodian requested that Gerion order his warriors to disarm themselves and accept that as the bearers of flawed gene-seed their very existence had now made them a danger to the Imperium.In that tense moment, one of Gerion's Astartes present on the bridge of the warship Lux-Imperatus raised his voice in protest, and was executed at once by Tyvar with his Guardian Spear.Gerion responded by opening fire upon Tyvar and ordering all of his Primaris Greyshields to seize the Torchbearer fleet, claiming that they were the ones who had been betrayed by the Custodians.A fight broke out on the bridge between the Primaris Marines and the agents of the Emperor, which ended with the death of Gerion and approximately ten of the Greyshields. In the wake of the Greyshields' rebellion, Tyvar proclaimed his intention to not rest until every Brazen Drakes Space Marine, old or new, lay dead.From Khassedur, Argento Corian, the so-called Enlightener, and the ragged remains of his Brazen Drakes Astartes fled final retribution. They made for the Nachmund Gauntlet and the perception of safety offered by the lawless wilds beyond in the Dark Imperium where the light of the Astronomican did not shine.In their wake, the Torchbearer fleet -- commanded by Adeptus Custodes Shield-Captain Atal Tyvar -- destroyed the Primaris gene-tech they had brought with them and executed the handful of surviving Brazen Drakes Greyshields, lest the taint of their Chapter's heresy run through their veins.Tyvar then vowed that he and his fleet would hunt the Enlightener to the ends of the galaxy, and set off in furious pursuit. Little did they suspect that news of the Brazen Drakes' treachery had made it back to Terra by secret channels, and that another Imperial force was mobilising elite assets to track Corian down and slay him...