Nathaniel Garro - Luna: After arriving in the Sol System with the news, Garro, his fellow seventy Death Guard Astartes, Euphrati Keeler, and Iacton Qruze were all placed in a fortress on Luna called the Somnus Citadel that belonged to the Sisters of Silence while the Emperor determined whether they were truthful or were simply further pawns of the Chaos Gods.Even upon reaching Luna, and with the news of the betrayal delivered, Garro's trials were still not over, as one of his Astartes, Solun Decius, had become infected with Nurgle's Rot aboard the Eisenstein. Wracked by constant pain, Solun finally gave in to the temptations of Nurgle to ease his suffering and allowed his corrupted body to be possessed and mutated by a Greater Daemon of Nurgle known as the Lord of Flies.His body was twisted by the possessing entity into a hideous daemonic form. In this state, Solun killed the two Astartes who had been conducting the death vigil over his prone form.The Lord of Flies went on a killing rampage throughout the fortress. Garro was forced to battle him throughout the Sister of Silence's citadel and out onto the barren, airless surface of Luna itself. He eventually bested the Daemon who had once been his trusted comrade and banished the hideous entity he had become back to the Warp.Afterwards, Garro, Qruze and the Sister of Silence Amendera Kendel were approached by Malcador the Sigillite, the Regent of Terra, and told that the Emperor needed them to form a new Imperial organisation, outside the boundaries of the existing Imperial bureaucracy, which would utilise "...men and women of inquisitive nature, hunters who might seek the witch, the traitor, the mutant, the xenos."The Emperor had foreseen that the end of the Horus Heresy would cost Him greatly, so much so that He would no longer be able to take an active hand in Mankind's survival.Yet He also knew that the threat of Chaos would not see defeat with Horus, but would continue to haunt Humanity. The very nature of the Horus Heresy had proven that the Space Marines were not immune to corruption as the Emperor had once hoped. So the Emperor set His hand to plans that would win a wider victory from the ashes of a most personal defeat.The Sigillite, closest of the Emperor's servants, was ordered to scour the galaxy for those that would be found worthy to help save the future of Humanity. This was a monumental task made all the more difficult by the anarchy created by the Warmaster's insurrection.That is how the Sigillite came to be on Luna, and the fate of Battle-Captain Garro became inextricably intertwined with the future survival of all Mankind.Under the Sigillite's own seal, Garro was tasked with finding 7 other Loyalist Astartes from amongst both the Loyalist and Traitor Legions who were utterly devoted to the Emperor and His Imperium in body and soul, as part of a new organisation of Astartes known as the Knights-Errant that would carry out classified missions given them by the Sigillite.Several of these Knights-Errant would eventually form the core leadership of what would later evolve into the Grey Knights Chapter of Astartes, the Chamber Militant of the Inquisition's Ordo Malleus. The Inquisition had been born in the fires of betrayal.