Isstvan III Atrocity - Conspiracy: The reconquest of Isstvan III provided Horus with the perfect opportunity to both amass those forces loyal to him without suspicion, and also rid his own XVIth Legion and those of his closest allies of those within their ranks whose loyalties were suspect and likely to stand with the Emperor in the event of civil war. The Isstvan System's distant location in the Ultima Segmentum and prevalent Warp Storms made it a perfect screen for the dark deeds that were to come, and orders were given for four Space Marine Legions, the Death Guard, Emperor's Children, World Eaters and the Warmaster's own Sons of Horus, to rendezvous at the Isstvan System, their approaches made to bypass the Warp Storms which raged to the galactic southwest of the system. Horus took this opportunity to use his authority as Warmaster and move the forces of the Imperial military as game-pieces on a board of Regicide to the configuration of his choosing that would be most advantageous once his revolt began. He commanded the Primarchs Lion El'Jonson, Sanguinius and Roboute Guilliman to muster their Legions in preparation for a series of missions in the Signus Cluster and Veridian Systems, each in dangerous and cut-off regions of space. Perceiving no obvious reason to doubt the Warmaster's motives, the three Primarchs set about planning their missions and transporting their Legions to the necessary staging points. So it was that three of the most powerful and staunchly Loyalist Legions -- the Dark Angels, the Blood Angels and the Ultramarines -- were sent by Horus to regions far from Terra and from the Isstvan System where they could not observe or intervene in what was to happen next. The rest of the Legiones Astartes -- the Night Lords, Alpha Legion, Iron Warriors, Raven Guard, Salamanders and Iron Hands -- were all actively involved in various campaigns and events across the Imperium. Safely occupied, their time would come later, be it for corruption or destruction. The Word Bearers were already long woven into the treachery that was to follow by ties that would not become apparent until much later. The White Scars and Imperial Fists were conducting operations in the Segmentum Solar and were too close to the Emperor for Horus to chance contacting them without raising suspicion whilst the Space Wolves and Thousand Sons were already caught up in a murderous machination, the Burning of Prospero, that had been long in the making.With humanity ignorant of the great and terrible events that were about to unfold, a massive war fleet gathered at the edges of the Isstvan System as elements of four Space Marine Legions began to arrive, and the first actions of the campaign were undertaken to destroy rebel outposts in the outer reaches of the star system as the fleet coalesced. The elite 1st Company of the Emperor's Children Legion led by Lord Commander Eidolon fought in concert with the Death Guard Legion's 7th Company under the command of Battle-Captain Nathaniel Garro against traitorous forces on Isstvan Extremis, the outermost planet within the Isstvan System. Whilst fighting against a powerful Slaaneshi psyker known as a Warsinger, Garro sustained serious injuries: crushing damage to his torso and arm as well as the loss of his right leg from the mid-thigh down. He was only saved from certain death by the timely ministrations of the Emperor's Children's Chief Apothecary Fabius. Taking stock of the desperate situation, the Lord Commander Eidolon made use of a hitherto unknown ability: a modified tracheal implant bonded with his vocal chords that allowed him to produce a nerve-paralysing shriek similar to that employed by certain warrior breeds of the xenos Laer. This powerful ability disrupted the Warsinger's attack, allowing Eidolon to get close enough for a killing blow and helped the Astartes carry the day, though its very existence was emblematic of the corruption that had already wormed its way deep into the heart of the Emperor's Children Legion.