Eisenstein - Luna: Stranded hundreds of light years from any stretch of inhabited space, Garro ordered the Eisenstein's shipmaster to overload the frigate's Warp-Drive and then jettison it out into space. Garro hoped that the detonation of the Warp-Drive would produce such a powerful signature in the Immaterium that any passing Imperial starships might be willing to stop and investigate. The plan would also guarantee that if no rescuers appeared, the Eisenstein would never reach another destination and its crew and passengers would die in the black desert of interstellar space.However, the ensuing explosion of the Warp-Drive echoed across the Warp and acted as a beacon for the Primarch Rogal Dorn and the fleet of his Imperial Fists Legion, who had been becalmed by Warp storms unleashed by the gathering power of the Dark Gods as the Horus Heresy began on their way back to Terra on the order of the Emperor. Dorn rescued Garro and his warriors, then scuttled the severely crippled Eisentein.Dorn proceeded to take the Eisenstein's survivors to Luna aboard the great mobile fortress-monastery Phalanx. While initially reluctant to the point of outraged violence to believe Garro about his brother Horus and the other primarchs' betrayal of the Emperor, once faced with overwhelming evidence from multiple sources, including the testimony of Iacton Qruze, a high-ranking member of Horus' own Sons of Horus Legion, he eventually relented and the Navigators of Dorn's massive fortress ship made their way to the Sol System where Dorn would inform his father the Emperor of this dreadful news.After arriving in the Sol System, Captain Garro, his fellow seventy Loyalist Death Guard Astartes, Euphrati Keeler, and Iacton Qruze were all placed in the Somnus Citadel, a fortress on Luna that belonged to the Sisters of Silence while the Emperor determined whether they were truthful or were 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 on board 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 Nurglish Daemon known as the Lord of the 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 citadel. Garro was forced to battle Decius 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 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, beyond 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."Under the Sigillite's own seal, Garro was tasked with finding 7 other Astartes from among both the Loyalist and Traitor Legions who were utterly devoted to the Emperor and His Imperium in body and soul. These Space Marines would become the Knights-Errant, several of whom would later become 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 and heroism.