Signus Campaign - Dark Secrets: When the Imperial Warmaster Horus, the greatest of the Emperor's genetic sons, fell to the temptations of the Chaos Gods and became swayed by their promises of power, he sought to persuade his brother Primarchs to his cause. Horus and Sanguinius, the Primarch of the Blood Angels Legion, had fought many campaigns by each other's side. Their relationship was so close it had even incited jealousy amongst their brother Primarchs on occasion. But in his blackened heart Horus knew that Sanguinius would never willingly betray their father the Emperor, and so he had formulated an audacious plan to either convert the Blood Angels Legion to his cause or utterly destroy them. To this end, Horus made use of a carefully guarded secret of the Blood Angels he had discovered solar decades earlier when he fought alongside Sanguinius' IX Legion in a xenocidal campaign on the world of Melchior.Horus had come upon his brother Primarch in the sunken ruin of an alien chapel and had witnessed the unthinkable -- Sanguinius murdering one of his own Astartes. Sanguinius had explained to his shocked and bewildred brother the reason for his actions. The angelic Primarch had discovered that within his own genome there was a flawed trait that lay buried and waiting to be awakened. During the Great Crusade, this strange affliction had begun to manifest, affecting some of the Blood Angels Legionaries over the course of several solar decades.The story was always the same -- a warrior of the IX Legion in the throes of battle eventually succumbed to a rage that continued to build to uncontrollable levels until his reason was lost. When a Blood Angels Battle-Brother succumbed to this affliction, his humanity would be stripped away until only his feral core remained and all the now blood-crazed Astartes wanted to do was kill and kill, satiating himself with blood and more blood. At the end, at the very worst of it, he lost every last piece of himself to the mindless rage, until death was truly a kindness.Fortunately, only a handful of Astartes had been afflicted over the course of two Terran centuries of continuous conflict. Most would perish in battle without anyone taking note of their growing insanity. But if their degeneration became noticeable, then Sanguinius himself, or the commander of the Blood Angels' elite Sanguinary Guard, Azkaellon, would usually be the one to end the life of the afflicted Battle-Brother. Yet, in the closing days of the Great Crusade, the emergence of this genetic Flaw began to occur more often. Sanguinius feared that, in time, the affliction would grow to encompass every member of the IX Legion.Sanguinius had been aware of the flaw in his genome and that of his sons in the IX Legion for several years by that time, and had chosen to keep the truth from the Emperor and his fellow Primarchs. He feared to speak of this to any of the others, for to do so would diminish his Legion in the eyes of his brothers and the Imperium. Some of his brother Primarchs would see it as a weakness and seek to turn this truth against him. Sanguinius was afraid to confide in the Emperor for he could not take the risk of being responsible for the erasure of the Blood Angels from Imperial history as had happened to the II and XI Legions.He was determined to not see a third empty plinth erected beneath the roof of the Hegemon in the Imperial Palace on Terra as the IX Legion's only memorial. Sanguinius continued to search for a solution but ultimately failed in this endeavour. Some of the Angel's sons had learned a measure of the truth, but only Azkaellon, First Captain Raldoron, the IX Legion's Master Apothecary on the Legion homeworld of Baal and a few others were fully aware of the extent of this affliction. They were united with Sanguinius in finding a way to repair this Flaw.Horus swore to his brother that he would never speak of this matter to anyone, even their father. And he promised that he would keep this promise for as long as Sanguinius wished him to. The Angel was touched by his brother's gesture and expressed his gratitude. Horus solemnly vowed to help Sanguinius deal with this matter, however long it took. Little did they know at that time, that one day a corrupted Horus would take full advantage of this knowledge and attempt to turn the Blood Angels' Flaw against them.