Markhov requested the assistance of the Ultramarines in investigating the planet Epsilon Regalis, which had recently turned away from the light of the Emperor for unknown reasons (later discovered to be the influence of a rogue psyker). Chapter Master Marneus Calgar consented and allowed the 4th Company, led by Captain Idaeus, to be seconded to his service. However, Markhov refused to disclose the nature of the heretic that they were after, stating bluntly that he had the tools to deal with it, which would later turn out to be his downfall as the Ultramarines were ill-prepared to face the threat that the psyker would pose.
Captain Idaeus, a contingent of Assault Marines, and the-then Veteran Sergeant Uriel Ventris were to attack the centre of the rebellion with the assistance of Markhov. While this was occurring, Veteran Sergeants Pasanius and Learchus were also headed to the battle within Rhino transports escorted by Predator Annihilators.
The assault marines landed in the midst of the rebel forces, and proceeded to rapidly kill the traitors in their path, slowly making their way to the leader of the heretic forces. However, the unbound psyker revealed himself and began wreaking havoc upon the ranks of the Ultramarines, seemingly withstanding the worst that they could throw at him.
It was at this time Markhov revealed himself, binding the psyker with the help of his aide, Arakoni, and tamed him by speaking the holy words of the Emperor. Markhov and the Space Marines then rallied together and carried their prisoner to the waiting Rhinos.
Aboard the Rhino transport, Markhov was surprised that the psyker was smiling, and told him that he had nothing to smile about, as he would soon be suffering the "torments of the damned." The psyker simply responded that it was Markhov who would do so, and not the psyker. Unbeknown to all, the psyker had retained some use of his powers despite the Inquisitor's best efforts, and managed to influence one of the battle brothers driving one of the escort Predators into firing upon the transport. In the ensuing chaos, the psyker was freed. However, instead of making his escape, the psyker attempted to wreak vengeance on his captors, killing Markhov in the process and destroying the escort vehicles, thus fulfilling his promise to Markhov that he would be "suffering the torments of the damned."
With the psyker's followers closing in, Ideaus determined that he could not be allowed to escape, and quickly ordered an attack run from the orbiting Thunderhawks, which eliminated the psyker once and for all. With the psyker dead, the populace were free of his malign influence and returned to normal.
For unknown reasons, all the events subsequent to the Ultramarines' deployment on Epsilon Regalis were later sealed by the Ordo Hereticus.