Eidolon - Drop Site Massacre: Final victory for the Traitors on Istvaan III had been bought with many lives, but in its wake the Traitor Legions were tempered in the crucible of combat to do what must be done to seize control of the Imperium. The process had been long and bloody, but the Warmaster's army was ready and eager to fight its brothers, where the lackeys of the Emperor would find their readiness to strike down their kith and kin untested. Such mercy would be their undoing, Horus promised. Horus would strike a vicious blow against the Imperium and the False Emperor -- a blow that would resonate down through the millennia for all time. The Warmaster still had to make preparations for the inevitable response of the Emperor, which was likely to arrive more quickly than anticipated and the Traitors needed to be prepared for it. Fulgrim was tasked to take a detail of Emperor's Children to the ruins of the alien fortresses that existed on Istvaan V and prepare that world for the final phase of the Istvaan operation. Fulgrim supervised the vast teams of Dark Mechanicus earthmovers as they shifted the black sand of Istvaan V and formed a vast network of earthworks, trenches, bunkers and redoubts that stretched along the ridge of the Urgall Plateau. Laagers of anti-aircraft batteries were set up in the shadow of the walls, and mighty orbital torpedoes on mobile launch vehicles hid in the warrens of an ancient alien fortress. If the Emperor's Legions wanted to destroy the Traitors, they were going to have to come down to the surface of Istvaan V to do so, as no obital bombardment would be powerful enough to dislodge the defenders or crack their resolve.Overcome with mind-numbing rage at their brothers' treachery, Ferrus Manus and his Iron Hands Legion gratefully received the Emperor's orders through his brother Rogal Dorn. In response to Horus' betrayal of the Loyalist Astartes in the Sons of Horus, Emperor's Children, World Eaters and Death Guard Legions at Istvaan III, the Primarch of the Imperial Fists Legion, Rogal Dorn, on the direction of the Emperor who had learned of Horus' actions from the Loyalist survivors aboard the Eisenstein, ordered seven Loyalist Space Marine Legions to Horus' base on the world of Istvaan V to put down the Warmaster's rebellion. They would attack in two waves and fall under the supreme command of the Iron Hands' Primarch Ferrus Manus. The Legions comprising the first wave were the Iron Hands, Salamanders, and the Raven Guard. The Legions comprising the second wave, who would arrive at Istvaan V after the first wave, were the Alpha Legion, Night Lords, Iron Warriors, and a large contingent of Word Bearers that their Primarch Lorgar had stationed in the star system. Unknown to Dorn and Ferrus Manus, the Night Lords, Alpha Legion, Iron Warriors and Word Bearers had all turned from their service to the Emperor and pledged their loyalty to Horus, and been instructed to keep their new allegiance to Chaos a secret.Caught between two armies, the first wave of the Loyalist forces were systematically massacred. Unrelenting gunfire from the Iron Warriors at the drop-site, and the resurgent forces along the Urgall Depression crushed the Salamanders and Raven Guard in a terrifying vice, and cut them to pieces in a murderous storm of fire and blood. Warriors of the Alpha Legion and Word Bearers followed their leaders onto the black plains of Istvaan V, their guns blazing and their Chainswords bright as they cast off the last remnants of their loyalty to the Emperor and turned their weapons on their brothers. What had begun as a battle had become a massacre, each pocket of Loyalist resistance gunned down with overwhelming superiority of fire, before the shredded survivors were hacked apart with bloody Chainswords.At the forefront of the Emperor's Children, Lord Commander Eidolon and the swordsman Lucius led a contingent of their warriors into the heart of the enemy, killing with wondrous displays of bladework and howling shrieks of raw sonic power. The swordsman danced through the battle, his Terran blade carving a screaming, bloody path as he laughed in time with music only he could hear. Within hours the slaughter was complete and almost the entire strength of three complete Legions lay silent and dead on the tortured sands of Isstvan V.