Hereon was the Blood Angels Chapter's High Chaplain when he traveled to the Angels Vermillion Homeworld Corinal in 428.M41 with his escorts. He had come to question the Angels Vermillion about the disappearance of the Imperium refugees that had come Corinal for safety after their world Dovar was invaded by Xenos. The High Chaplain noted that, while the Imperial Navy transports that had carried the refuges to Cronial were still in the world's orbit, there was no signs of life aboard them. The Chapter refused Hereon's request to land upon Corinal to determine the status of the refuges, and demanded that the Blood Angels leave their world. When Hereon refused to leave until he discovered what happened to the Dovar refugees, the Angels Vermillion's defensive weaponry targeted the High Chaplain's vessel, the Eminence Sanguis. However, their Chapter Master Chauld reluctantly agreed to meet with Hereon on the Chapter's orbital fortress when the High Chaplain stated that firing on his vessel would be considered a declaration of war by the Blood Angels. Once Hereon was on the orbital fortress, Chauld showed him what had happened to the majority of the refuges that had been under their care. To Hereon's horror he saw that the Angels Vermillion were draining the Dovar refuges of their blood so that the Chapter could later feed upon it. Chauld calmly stated that the refuges had the misfortune of arriving on Croninal while the Chapter was undergoing The Sorrowing ritual.
The Chapter Master then explained that their blood would be put into the Angels Vermillion's power armour dispensers, and in that way the Chapter kept the Black Rage at bay for decades and only a few of their Battle Brothers fell into the grips of the Red Thirst each year. He went on to say that the remainder of the refuges would be forced to serve his Chapter as thralls, until they too took part in The Sorrowing. When Chauld was finished, Hereon was shocked at the abomination of a ritual the Chapter had been perpetuating in secret for millennia and vowed to put a stop to it. The High Chaplain then tried to kill Chauld, but the Chapter Master's Sanguinary Guard intervened. In the brief battle that followed, the High Chaplain managed to kill two of the Guard before they pinned him to the ground. Chauld, however, forbade them from harming or killing Hereon, though not out of any respect for the High Chaplain. The Chapter Master knew that if Hereon was killed by them, the Blood Angels and their Successor Chapters would hunt down and destroy the Angels Vermillion. Instead, Chauld threatened that if the Blood Angels ever moved against his Chapter for what happened to the Dovar refuges or for conducting The Sorrowing, then he would reveal the existence of the Red Thirst and Black Rage to the Inquisition. If the Angels Vermillion were to be destroyed, Chauld warned, then they would ensure all of the Sons of Sanguinius would die as well. Seeing that he had no choice, Hereon reluctantly agreed to leave and would make excuses for the disappearance of the refuges. When he returned to Baal, however, Hereon informed his Chapter Master of the horrors their Successor Chapter had committed and Dante immediately ordered that the Angels Vermillion be shunned and their aid was never to be accepted by the Blood Angels.