Horus spoke to his brothers, and they listened. Even Fulgrim, who loathed letting anyone but himself holding the spotlight; even Angron, whose every thought was consumed by bloodlust, hatred and pain. The Warmaster did not try to assign blame for their defeat at Terra. Instead, he claimed that while they had been forced to retreat, they had still succeeded in accomplishing the rebellion's first and most important goal. Horus raised his Talon, and all present saw the red streaks of the Emperor's own blood, forever marking the metal of the weapon forged by Kelbor-Hal.
Though Horus was careful not to proclaim the False Emperor dead yet, he confidently declared that He had been crippled, His plans to enslave Mankind and turn the species into fodder for His ascension to godhood in ruins. Now, they, the true heirs of the Great Crusade's legacy, must free the galaxy from His lies and carve the future of Mankind across the stars.
It was as Horus was about to lay down his vision for the Long War that Lorgar made his move. By that point, less than ten minutes had passed since the last arrival and the beginning of the Conclave.
"No matter how you try to disguise it, the truth remains, brother. You lost. You failed, just as I knew you would. You are weak, Horus. You held the galaxy in your grasp and you let it slip away."
Lorgar to Horus, at the Broken Conclave
Lorgar drew his weapon, the crozius named Illuminarum, which had been forged for him by Ferrus Manus in an earlier, more innocent age. As he did so, Erebus and Kor Phaeron spoke un-words of command, and the seventeen figures which had accompanied the Aurelian threw off their hoods, revealing themselves as Daemonhosts of great power, their true nature concealed thus far by the ritual wardings carved onto the flesh of their mortal vessels. Bound by the will of the Dark Apostle and the Master of the Faith, these infernal creations of the Word Bearers launched themselves at Horus, while Lorgar gathered his own power to strike, reciting words from a language that had been dead before Mankind had risen from Old Earth's primordial slime.
At the sight of Lorgar's assault, the other Primarchs began to move to intervene, though it wasn't certain in whose favor. But before any of them could reach the confrontation, Magnus the Red and his sons raised a barrier separating Horus and his would-be killers from the rest of the room. The Crimson King glared at the Warmaster, his one eye filled with hatred.
"Did you really think I did not know who it was that told Russ to kill me and my sons ? Did you really think me so blind to your manipulations, brother ? I knew. I have always known, from the moment the Wolves came to burn all that I had wrought. And now, you will pay."
Magnus to Horus, at the Broken Conclave
Seeking vengeance for the fate of Prospero, Magnus had contacted Lorgar as soon as the call to the Conclave had been sent. The Crimson King and the Aurelian had once been friends as well as brothers, before Magnus' reticence in helping Lorgar's downfall to Chaos and his own growing madness after his maiming at Russ' hands had soured their relationship. Speaking mind-to-mind over incomprehensible distances, the two Primarchs had forged an alliance, united in their common opposition to Horus. Both of them wanted the Warmaster dead, and the Conclave was their best shot at eliminating him.
Even as Horus fought off the Daemonhosts, he could see his hopes of uniting the Traitor Legions under his leadership once more turn to dust in the corner of his eyes. The divisive nature of Chaos was reasserting itself now that Lorgar had broken the truce.
Enraged by the use of sorcery, Angron lost what little control he had, and launched himself at the Crimson King. His first blow was repelled by another psychic shield, and before he could strike again, Fulgrim burrowed a long, needle-thin blade into his back, laughing all the while. Mortarion attacked Magnus as well, his long-held disdain of sorcery only strengthened by his allegiance to Nurgle, the Dark God opposed to Tzeentch, Magnus' own puppetmaster. Perturabo's Iron Circle had surrounded him, shielding him from the mayhem while the Lord of Iron watched it all unfold with dispassionate eyes. Alpharius was already gone, vanished back into the shadows from which he had appeared, and Curze was observing the scene with a wide, crazed smile while his warriors remained at his side, weapons drawn, but unsure what their lord wanted them to do.
All of this happened in the time it took Horus to dispatch all seventeen Daemonhosts. Less than ten seconds had passed since the beginning of the hostilities, but it had been enough for Lorgar to gather his strength. With a great cry that was half-triumph, half-prayer to the Dark Gods, Lorgar unleashed his spell upon the Warmaster.
The curse was ancient, and amplified by Lorgar's terrible power. Reality cracked and bled as it flew, leaving a trail blackness through which hungry eyes peered, only to withdraw as they took in just who was present on the other side of the rift. It struck Horus in the chest, and for a moment the Warmaster stumbled, his face paling, the dark fire of his aura flickering.
Then, suddenly, Horus stood straight, his eyes aflame with power, Lorgar's curse slipping from him impotently. He marched toward Lorgar, who raised his weapon in defence, only for Illuminarum to be knocked aside by a casual blow before Horus rammed the Talon into his chest with such strength that the armored Primarch was lifted up the ground. As the claws of the Talon met the wards of Lorgar's armor, a psychic shockwave filled the room, and the four Daemon Primarchs felt their power diminish as the attention of their patron gods was now turned elsewhere.
Lorgar, his chest pierced by the Talon, his blood flowing from the wounds in torrent, ignited. On the verge of death, the Arch-Priest of the Primordial Truth was receiving his masters' ultimate blessing – and their most terrible curse. The blades of the Talon slipped free as Lorgar's gene-forged flesh dissolved. A horned, blazing skull glared at the Warmaster, before a blow from Worldbreaker shattered the hold on corporeality of the newly ascended Daemon Primarch. With a bitter laugh and the promise that this was merely the beginning of Horus' torments, Lorgar vanished. With his departure, the ambient Warp energies plummeted, and the four other God-marked Daemon Primarchs also faded away, Angron with a terrible scream of rage, Fulgrim with a pristine, mocking laughter, Mortarion with a series of Barbarian curses, and Magnus with one last enigmatic glance at Horus before drawing his sons along with him. Only Perturabo remained, his physical form maintained by the technomancy infused within his Warped flesh.
Horus turned to where Erebus and Kor Phaeron had stood, but the two Word Bearers were also gone, using their sorcery to escape his wrath and flee back to the Trisagion, which was already turning to plunge back into the storm. The rest of the gathered ships were also departing, only the Vengeful Spirit and the Umbrea Insidior remaining behind. After one last exchange with Horus, Perturabo teleported back aboard the Ironblood, and left Zu'lasa as well.
"I have heard your plans, and I do believe they have merit. But Magnus is my brother too, Horus, and you sent the Wolves after him. I will not command my sons to die in a war waged for your pride. Prove that you are still worthy of my loyalty, and I shall be at your side until the end."
Perturabo to Horus, at the Broken Conclave
Only Curze and his escort remained behind. As Horus looked upon him, wondering what his mad sibling would do next, the Night Haunter bowed before the Warmaster, promptly followed by his sons, who knelt before the chosen champion of the Ruinous Powers. Never before, not even when the Traitor Legions had gathered on Isstvaan, had Curze displayed such submission to Horus. Konrad promised his brother that his Legion would stand alongside his own against his enemies, the Thousand Sons and the Word Bearers.
For a long moment, Horus watched Curze, before nodding, accepting the offer. Then he returned to the Vengeful Spirit, and the ship set course for Maeleum while Curze returned to Kerlazium to make preparations for what was to come.
Alone on his black throne the walls around him trembling softly in rythm with the engines of the Vengeful Spirit, every door and secret passage locked and guarded by his faithful Justaerin, Horus finally allowed himself to relax. His calm mask collapsed into a grimace of pain. Blood seeped from the wound in his side, where the Emperor had struck him in their duel.
Lorgar's attack had forced him to use all of his power to counter it, and in the time that had taken, the wound had opened again. He was confident he had managed to hide it from the rest of his brothers, but if any of them ever discovered the truth … If they ever discovered that he could no longer use the fullness of his might for more than a handful of seconds before that wound reopened and he started bleeding out … There was no telling how even his sons would react.
He could no longer take risks like the conclave had been. For now, all his brothers had seen was that he was still as strong as ever : even Lorgar, with his cowardly ambush and the help of Magnus, had not been able to take him down. But he could not fight on the front lines of this new War, lest his condition be exposed. Instead of a warrior-king, he needed to be a general, guiding his troops and only taking to the field in controlled conditions.
He would triumph, no matter what. He would cast his father down, and rule over Mankind. The defeat at the Siege, his wound, Lorgar's and Magnus' petulant rebellion : those were naught but setbacks. No matter what obstacles fate placed in his way, victory would be his.
And so began the Legion Wars.