Though most Traitor Legions fled to the Eye of Terror in the wake of their defeat at Terra, the Night Lords did not – at least, not immediately. Apart from the Alpha Legion, the Night Lords were the only Legion following Horus who had not wholly embraced Chaos, though that was more due to a lack of proper leadership for the Ruinous Powers to influence and manipulate than to any moral fiber the child-killers of Nostramo may possess. Of all the Traitor Legions, the Eighth had long been the most feared and despised, long before the Warmaster had raised the banner of rebellion.
Scattered across the galaxy at the end of the Thramas Crusade and their Primarch's disappearance, the Night Lords had no unified chain of command. Only a portion of the Legion had taken part in the Siege of Terra, led by warlords who sought the glory of burning the Throneworld, or had thought to earn the Warmaster's favor by adding their forces to his. And when Horus fell at the Emperor's blade, they were all too quick to abandon the fight, retreating from the Solar system.
Fleeing from the retribution of the Imperials, these Night Lords eventually came together on Tsagualsa, which had once served as their stronghold during the Heresy. There they found their missing Primarch, Konrad Curze, waiting for them after his long absence, which had caused many of his sons to believe him dead. The Night Haunter, whose insanity had grown progressively worse during the rebellion, was now on the very edge of complete madness, as the future he had believed fixed had proved to be mutable after all. Sanguinius hadn't died on the Vengeful Spirit as both Konrad and the Angel had thought, had known he would, and the fragile edifice of justifications and twisted beliefs used by the Primarch to avoid facing the full extant of his sins was collapsing.
Despite their father's manifest instability and the doubts many of them had expressed about his leadership in the past, like broken dogs returning to an abusive master, the Night Lords once more bent the knee to their gene-sire. News of Curze's reappearance spread, and the scattered forces of the Eighth Legion gathered at Tsagualsa, leaving trails of traumatized worlds in their wake. There, in a brief moment of clarity, Curze commanded that his Legion immediately leave for the Eye of Terror. There, he told his sons, they would find Horus Lupercal, and the Warmaster would give him the answers he needed to decide on the Legion's future course.
With the Primarch's sanity still fluctuating wildly and the First Captain Sevatar missing, overall command of the Night Lords fell to a newly reunited Kyroptera. Those members of the exalted circle who had been elevated to it by Sevatar after the disastrous Thramas Crusade and had survived the following years of conflict formed the core of the group, complemented by other warlords who had proven their cunning and might (or who simply had too many warriors or resources under their command to ignore). Bound by the will of the Night Haunter, the Kyroptera made preparations for the Night Lords to abandon Tsagualsa and follow the rest of the Traitor Legions to the Eye.
Konrad Curze entered the Eye at the head of a fleet of tens of thousands of Legionaries, which was perhaps the largest single military force in the entire Eye of Terror, due to the dispersion of the other Traitor Legions. Only the Sons of Horus under the Warmaster could match the number of Astartes in the Night Haunter's great armada. But those numbers counted for little against the dangers of the Eye. Here, in the grave-birth of Slaanesh, reality was shaped by the sins and hidden desires of the living and the dead, and Konrad Curze's spirit blazed very bright indeed, though it was a pale and baleful light. The moment the Eighth Legion entered the Eye, it was beset by the manifestations of its Primarch's nightmares – abominable things spawned from his broken psyche.
The Night Lords fought, led by their Captains and Lords, while the Primarch remained aboard his flagship, battling against the powers, the self-doubt and self-hatred that would see him and his Legion destroyed. Eventually, the nightmares relented, and the Eighth Legion found itself near a world orbiting a black, lightless star, that nonetheless radiated a baleful heat upon the daemon world. Upon that world were vast mountains of black mineral, which was bitterly familiar to the scanners of the Eighth Legion : adamantium, an entire world worth of it, far more than there had ever been on the Legion's lost homeworld of Nostramo.
Though the planet was cold and devoid of life, it was not uninhabited. Millions of pale humanoids wandered amidst the obsidian mountains : the souls of every criminal the Eighth Legion had ever slain, condemned to be reborn in a cruel un-life, their previous lives half-remembered, fit only to torment them with the knowledge that they had once been alive. A great number of these damned souls came from Nostramo, the world that the Night Lords had destroyed at the command of their Primarch, watching it burn and crack apart under the focused fire of their fleet. There were many more from all the worlds the Eighth Legion had brought to compliance and butchered during the rebellion, but out of all those the Night Lords had slaughtered, less than one in a hundred had been judged corrupt enough to be dragged from the Empyrean and cast upon this daemon world.
As the Kyroptera wondered about the strangeness of this world, Konrad Curze emerged from his isolation. His cursed sight had granted him a vision : this unholy world held the key to his fate, if he would but descend upon it. At his command, the Night Lords descended upon the daemon world en masse, thousands of midnight-clad Legionaries falling from the Warp-torn heavens. The damned ran from them in terror, remembering the image of the bat-winged skull even through the shroud that laid upon their minds. For now, the Night Lords did not pursue : they followed their lord as he walked amidst the ragged, sharp edges of adamantium, seeking something, not knowing what.
Eventually, deep within a valley borded by high, black peaks, Konrad found the entrance to a cave. He bade his warriors wait for him outside, and descended into the heart of the daemon world. What he found there, none but the Dark Gods know, but when he returned, he was transfigured.
'N-no ...'
'Yes.'
'It … it cannot be ...'
'It is. It must. It has always been.'
'But … vindication ...'
'Is a lie. Give in. Let go, Konrad. Let go of your regrets. Let go of your weakness. Become … what you know you must be.'
'Ah … aaaAAAAHHHAAAAAAAAAHAHAHAHAHAHAHAHAHAHAHA !'
Gone was the wasting, melancholic figure of the madman whose grip on sanity had ever been slipping : Curze had embraced the evil that defined him in the eyes of the Imperium wholly. His hands were dripping in some black ichor that burned through the adamantium as it dripped. His skeletal-thin body was overflowing with the energies of the Warp, and for the first time he felt that the visions granted to him by his second sight were clear. He now knew what awaited him, what he had always been fated to : an eternity of judgment, punishing those who had sinned – and every soul in the galaxy was guilty in the eyes of the reforged Night Haunter. He could see his future and that of his sons, and it was glorious. His warriors, upon seeing him emerge from the cave, fell to their knees, shouting their devotion to their King of the Night, and Curze bathed in their worship, and smiled. It was the first time he had ever done so in response to his sons displaying their love and fear of him : perhaps that should have been a warning to the Night Lords of what was to come.
The Night Haunter named this world Kerlazium, which in Nostraman meant "Resurrection", and set his sons to the task of bringing punishment to the damned that inhabited it. They set to their work with great enthusiasm, for the cruelty that had been their hallmark during the Great Crusade and the Heresy that had followed had only grown since their entry into the realm of the Dark Gods. And the damned, while already dead, were incredibly resilient, able to withstand punishment that would have killed a hundred men before finally dissolving into mewling ectoplasm, all trace of their former identity erased by the tortures they had endured.
Soon, it was discovered that the damned, when tortured, produced a strange, crimson liquid, akin to blood but inbued with strange energies. Drinking that liquid provided a living being, be they mortal or Astartes, with a rush of sensation and strength, as well as healing wounds and serving as nourishment – the only sustenance that could be harvested on the cold, lifeless rock that was Kerlazium. The Night Lords began to harvest this liquid, which they named akhrali, and used it to fuel their own transhuman bodies and that of their mortal slaves. The Warp, with typical dark humor, had granted Curze's greatest wish : now, the torments he inflicted would serve a purpose.
With the labour of the damned, the sons of Konrad Curze built great palaces of pain, where millions of souls were subjected to unspeakable torments while the Night Lords themselves attended to the damned who deserved their personal attention for their sins. Whether there was any true justice in how the fate of the damned was decided, only the Dark Gods know.
The bulk of the damned were herded into the mines that exploited the adamantium, using the material to repair the Legion's damaged ships. The favored mortals of the Night Lords were allowed to build cities among the priceless black stone, protected from the depredations of their most degenerate masters by those who retained a modicum, if not of honor or compassion, then pragmatism. Under the leadership of Zso Sahaal, Talonmaster and First Captain of the Legion, those few warriors clinging to their sanity and the prospect of the Long War built a kingdom under the endless night. They traded the spoils of industry to the torturer clans, in exchange for the essence they needed to sustain themselves and their servants.
Curze built his own palace at the center of this kingdom, and the greatest monsters among the rest of his sons came to visit him and pay tribute, forcing the faithful of the Long War to witness first-hand the corruption that was seeping into their Legion – a corruption that originated from their Primarch, who had in the Eye become at last what he had always threatened to be. Yet their loyalty to the Night Haunter remained unshakeable, whether by devotion or dread.
In time, Horus came to Kerlazium, drawn by the echoes of the Night Lords' atrocities. In the chambers of the Living Palace, built from the meshed flesh of slaves and damned alike, the Warmaster conferred with the Night Haunter, away from the eyes and ears of their sons. For an entire day, the two Primarchs spoke, and when they were done, Curze had agreed to take part in the Warmaster's next grand endeavour : a conclave, gathering all the exiled sons of the False Emperor, to discuss the War that must be waged against the Tyrant of Terra and His slaves.