Isstvan III Atrocity - Wrath and Ruin: Even before the first treacherous blow was struck, Horus' grand plan had, unknown to him, begun to unravel. Before the virus-bombs fell, the impending atrocity had been discovered by several Astartes among the orbiting fleet who remained loyal to their Emperor and their comrades and who resisted. Chief among these was Battle-Captain Nathaniel Garro of the Death Guard, a Terran Veteran and one of the original recruits of the XIV Legion. Garro acted swiftly, rallying Loyalists to him and successfully commandeering the Death Guard's Heavy Frigate Eisenstein. Garro broadcast warning messages of the Warmaster's treachery to his Battle-Brothers on the planet's surface.Elsewhere amid the Emperor's Children's fleet, Captain Saul Tarvitz, a line officer of his Legion who had long harboured deep suspicions about his Legion's growing secrecy and unorthodox actions, had uncovered the truth of the coming betrayal mere minutes before the onslaught was to begin. Powerless to prevent what was to come, Tarvitz stole a waiting Thunderhawk gunship and descended to the planet's surface, carrying his own warning of the horror that was about to be unleashed. Those that heard or passed on Tarvitz's warning took air-tight shelter before the virus-bombs struck.The World Eaters on the planet's surface were the furthest from cover and suffered the worst of the initial bombardment. Some had reached the safety of the bunkers, but many more had not. Superhuman warriors fell to their knees as the lethal virus penetrated their armoured bodies, deadly corrosive agents laced into the viral structure of the biological weapon dissolving exposed pipes and armour joints, or finding its way inside through battle damage already suffered by the armour. Astartes screamed. The sound was all the more shocking for its very existence rather than for the horror of its tone. The Life-eater Virus broke down cellular bonds at the molecular level and its victims literally dissolved into a soup of rancid meat within minutes of exposure, leaving little but sloshing suits of rotted armour. Even many of those Space Marines who reached the safety of the sealed bunkers died in agony as they shut the doors only to find they had brought the lethal virus inside with them. When the firestorm began after the initial bombardment, those Astartes who had survived the viral attack by sealing their suits of armour against biological attack found themselves consumed in flames as they desperately sought to find cover once more. But against this firestorm there could be no cover for those who had dared to brave the elements.Receiving no such warning, others were not so fortunate however, and many Loyalists and suspected Loyalists not assigned to the ground attack looked on in shock as the virus bombs fell, only to find knives waiting for their backs. Many resisted valiantly but, caught utterly unprepared for such perfidy, were destroyed. This fate not only awaited Loyalist Space Marines but others, including large numbers of human Imperial Army auxiliary troops, support staff, Imperial Iterators and functionaries who, caught up within the ships of the fleet, were massacred as the Legionaries loyal to Horus in their midst turned on them with merciless violence. Even here, however, not all went to plan and the "mere" mortals, in many cases underestimated by their superhuman Astartes betrayers, put up considerable resistance or fled into the bowels of the great ships and had to be hunted down at length, often carrying out campaigns of sabotage in the process.During the orbital attack at least one torpedo-monitor, the Ducroix, remained in Loyalist hands and turned its firepower on the Traitor warships in a futile attempt to interdict the bombardment, destroying several Escort ships and inflicting significant damage on the Battleship Killing Star before it was ripped apart by Traitor fire. Having refused the order to surrender, the Mechanicus Ordo Reductor Galleass Xerxes 9-7-7, a vessel that had joined the fleet late and was not part of Horus' plans, also had to be shot down at considerable cost to its attackers, its disintegrating hulk descending into Isstvan III's burning skies and lost amid the flames consuming the world. As this was occurring on the fringes of the fleet cordon, the Heavy Cruiser Sunstone was the scene of a protracted on-board struggle. Here the sworn Lifeguard of the Terran Plenipotentiary, the renowned Duke Mortecher, turned what should have been a simple takeover of the ship by a delegation of the Emperor's Children and the assassination of the Council of Terra's primary representative to the Great Crusade, into a frantic deck-by-deck battle for control of the vessel. It is not known what was to finally occur aboard the Sunstone, but as the firestorm raged on Isstvan III below, the Terran warship suffered a catastrophic detonation in her forward magazine, leaving the Sunstone a splintered wreck.