Aboard the Vengeful Spirit, the Sons of Horus were growing increasingly desperate. For the third time in the Legion's history, their Primarch was dying, and it seemed there was nothing they could do. Then the Sorcerers came to their commanders, and told them that the Dark Gods had spoken to them : Horus would survive, if they brought him to their realm. Taking command of the Legion, First Captain Abaddon ordered that the course be set for the Eye of Terror. Entering the Eye was difficult, for the Sons of Horus had never had the need to visit it, but they managed to survive its tides, though they had to force the Navigators to pass through the Cadian Gate. Once the tides receeded, they found themselves orbiting a strange world, where the Sorcerers told them something was waiting for them. The single structure on the planet was a citadel, which looked like something a child might have built out of sand after seeing a few strongholds but without understanding them.
The Sons of Horus brought their father to the fortress, its gates opening of their own accord as they approached. The deeper in they went, the more disturbing their surroundings became, as the normality of the fortress' exterior started to reflect the madness of the realm in which the Traitor Marines now dwelled. By the time they reached the throneroom, where Kairos Fateweaver waited for them, the Astartes were carrying their father's stasis sarcophagus through what seemed to be the inside of a living thing, with the walls pulsating in rhythm to distant heartbeats and gears of silver and bronze turning amidst the flesh.
He wanted to scream, but he couldn't.
He was frozen within a single moment of agony, the wound on his side burning through his very soul with the fire of his father's blade. There was no change in the pain : it never grew nor diminished, and he never grew used to it. He couldn't think, because his brain was suspended in stasis along with his body, but his soul still felt an eternity of pain.
Finally, the pain receded, though it would never leave him completely. He opened his eyes, and saw a great two-headed humanoid bird tower above him, looking at him with malice and amusement in its black, beady eyes. There was blood dripping from its beaks, transhuman red.
'Awaken, Prince of the Eye,' said one of the heads. 'It is time to claim your destiny.'
'Awaken, Sacrificed King,' said the other. 'It is time to break the chains of your fate.'
Only four Sons of Horus entered the throneroom, carrying Horus' sarcophagus with them. For several hours, they remained secluded with the Daemon Lord, the warriors gathered outside growing more and more impatient. Then the gates opened, and Horus Lupercal strode out, flanked by only two of the four warriors who had carried him inside : Ezekyle Abaddon and Falkus Kibre. Of the two other warriors, there was no trace to be seen, anymore than there was of Kairos.
Horus had been healed, Kairos calling upon the power of Chaos that still dwelled within the Warmaster to undo the damage inflicted by the Emperor's sword – or so it seemed at first. In truth, though Horus was up and walking, and seemed completely healed, the wound was still raw, threatening to tear open with every move. The Master of Mankind had struck Horus on his flank, opposite to where Russ had struck him with the Spear given to him by their father months ago. That wound had nearly killed him, and this one had been a magnitude of order worse. Under his repaired armor, Horus was still bleeding, still in pain, though he made sure not to show it to his sons.
They left the false fortress, which collapsed right after they exited it. There Horus adressed his sons, who had all come down to the daemon world, awaiting news of their father. Their great rebellion, for which they had thrown away everything they had ever been and believed in, had failed : now more than ever, they needed the First Primarch to speak to them, to tell them what they would do in this strange realm where they now found themselves. Thousands of Legionaries stood at attention, roaring their joy as their Primarch emerged from the fortress, seemingly restored.
In one hand, Horus held Worldbreaker, while the other was clad in the Talon of Horus, still red with the Emperor's own vitae. The Warmaster raised the claws up for all to see the bloody evidence of his deeds, and began to speak. He told them of how he had faced his father aboard the Vengeful Spirit, how he had been struck down at the same time he had dealt a mortal blow to the tyrant, and how he had been healed by the interventions of the Warp-dwelling Powers with which they had allied themselves against the False Emperor.
He told them how they could not return to the galaxy right now : his loyalist brothers, blind to their father's true nature, would destroy them if they did. They needed to rebuild first, here in this realm where the Imperials could not follow. Though the rebels had been defeated, they had achieved their primary goal, the great cause for which they had turned against the Emperor in the first place : the self-proclaimed Master of Mankind was dead, and His plans to enslave Humanity in order to achieve godhood were dust. He reminded them of how, when he had first made the choice to rebel, he had asked them what they would be willing to sacrifice to accomplish that goal.
Horus spoke of the wonders they would find and create, of the glory they would earn in the Eye, where the slaves of the False Emperor could not pursue them. He exposed to them his vision of a new empire, built free from the shackles of the False Emperor and His councils of petty bureaucrats. Let the leaderless Imperium believe them dead, or imprisoned within the madness of the Eye. Here they would rebuild, prepare, and when the time was right they would return to the galaxy and take the remains of the Imperium for their own. It would be a long and difficult journey, and there was no doubt that they would face many trials on the way, but the Warmaster promised to his sons that in the end, they would prevail. And they believed him, because they had nothing else left but him.
The reconstruction process would begin on this daemon world, which Horus named Maeleum. There the Sons of Horus built their great stronghold, Lupercalia, upon the very site of the false fortress where their Primarch had been healed. They experimented with the strange properties of the daemon world, discovering that a strong will could reshape its surroundings as it pleased – and no will was stronger than that of Horus. The Warmaster imposed his will upon Maeleum, creating a large river flowing from the heart of Lupercalia that could be used as water sources (though even Horus' will could not create clean water outright, and it had to be filtered and purified before being fit for consumption). Lesser strongholds were built as the Sons of Horus tightened their hold on the planet, each the domain of an officer of the Legion.
The tech-priests of the Dark Mechanicum aboard the Sixteenth Legion's fleet explored the system, discovering several areas rich in mineral resources, which they immediately set about exploiting in order to repair the battered ships of their Astartes masters. Space stations and orbital docks were constructed around Maeleum, while small flotillas were sent out to explore the Eye of Terror and locate the resources required to build the new empire. Horus gave another task to these warbands : they were to find if any of their allies had also made it to the Eye, and establish contact so that the great army that had laid siege to Terra might be forged anew.