Bridge of the Vengeful Spirit:
Horus Lupercal, Warmaster and victorious commander of the Legions of Chaos, stared at his father, the mighty Emperor and Master of Mankind. Looking with contempt at his father over the corpse of his brother, the blessed Sanguinius, he kicked the corpse forward, callously leaning forward and smiling.
"Is my dear brother Perturabo here? I do hope his mediocrity didn't harm you in the Siege of your Palace, my callous betraying gene-sire."
The Emperor looked at Horus quietly, his Sword beginning to glow with the sheer essence of his own Psyker abilities.
"You are a fool, supposed Master of Mankind. Against you the Lords Four have raised a great banner. They would grant Mankind all that it wills, they would make us still greater than ever we imagined ourselves to be! You are a timid weakling who cowers before the great Gods, but if you in your timidity knelt before me, I will spare your life. I might even keep you as a jester to my own court as the Emperor Lupercal, Master of Mankind by the will of the Gods!"
The Emperor looked at Horus.
"No mortal is the master of Chaos. It uses you, you do not use it."
Snarling, Horus prepared crackling energy only to see Perturabo marching toward him. With a sudden and swift movement he hurled the blast at his brother only to his surprise to see the Iron Warriors Primarch easily dodge the electricity, raising a bolter whose presence caused both Horus and the Emperor to register shock and a strange reaction.
As he noticed this, Horus also saw his own abilities seemingly weakening.
"Horus the arch-traitor, you shall atone for all your crimes against the Imperium! Against our father! Against our brothers, slain on the battlefield of Isstvan V!"
Horus growled with a rumbling bestial tone.
"If Rogal Dorn hadn't joined me, you would not have been overly concerned about this. You might have even joined me, your precious world a bonfire."
Perturabo smiled, a grim, cruel, and more than somewhat sinister smile.
"It is more than true that the mere presence of Dorn and his sons as traitors made my loyalty an assurance. But I know now, my dear brother, why my Legion was so over-stretched. I know which skulking coward attempted to break us, to make me burn my world. I know which maniacal egotist engaged in such a crime against not only nature and the rationality that Imperial Truth might have brought, but let a galaxy burn because his precious ego was offended.
I never did trust my father's wisdom in making your Warmaster, and this foul civil war you have unleashed only validates that distrust. In the memory of my brother Ferrus, a martyr to your war, and to the blessed Sanguinius, my bolter shall humble even the strutting monster who adores the so-called Gods in the Warp! I have had explained to me by the Sigilite the nature of what you serve.
These are no Gods, these are the manifestations of all the evil and filth in the universe, an evil and filth you slake as long as you draw breath. Even now other Primarchs rally to our cause."
Growling, Horus strode closer to Perturabo, who saw the chink in his brother's armor and suddenly formed a very grim smile indeed, one that brought Horus to a halt.
"Tell me, willing servant of the Warp, what happens to those addicted to Chaos if you are struck by bullets hallowed with the power of Blanks?"
Horus's eyes suddenly widened and he took a step back.
"Yes, brother, weapons hallowed by the blood of a Sister of Silence your treacherous betrayers slew."
With that he fired his bolter four times, the strikes ones Horus attempted to disrupt with the electricity he'd stored up but the rounds passed harmlessly through the electricity and slammed into the chink in his armor. Four perfect shots, the kind only a Primarch could make. The weapons hallowed by the power of the Blank struck Horus with a resounding set of wet thuds that led the Arch-Traitor to roar in pain.
As he staggered back, Perturabo took from his back the massive Thunder Hammer that he'd made infamous in his vendetta against the traitor Dorn and the legions of Horus in that order. The mighty Worldbreaker, product of Olympias, hallowed by the power of the Lectio Divinitatus. It was a gilded Warhammer, glowing still further with a crackling orange energy that took blasts of electricity from Horus and dissipated them harmlessly.
As he strode forward and raised his hammer toward Horus, his downward swing was blocked by none other than his father. The reason why was apparent, as Horus had sunk to his knees, blood not stopping, his face no longer glowing with the fell red light of the Warp. Instead he was crying, looking at his father and Perturabo.
"I see it now." The rumbling power was gone. The voice was a quivering whisper of a wreck, of a shell where there had been power.
"You were right. They lied to me, they deceived me, they made me betray everything that I was. Father, I wish to die as myself. Don't let Perturabo kill me for vengeance, when the red haze of anger fades it will never sit well on his conscience." The Emperor looked at his son in a mask of despair.
"You are right, my son. Forgive me for failing you, as I failed all humanity. I wished that people could triumph over the most bestial elements of the Immaterium with their own highest instincts. Man was not as much as I believed him to be, nor the supermen I made in my image." Sighing, the Emperor then turned to Horus and a sudden and powerful blast of Soulfire flared, Horus dying with a smile as his soul was utterly eradicated and spared the attentions of the Chaos Gods.
There, on the bridge of the Vengeful Spirit, stood the Emperor and then the legions of Chaos began to prepare to flee. As the Emperor teleported his sons and servants away, he returned to his palace and to the Golden Throne, architect of his misfortunes. Looking at it he saw a glimpse of a future that could have been, his body a rotting corpse maintained by the sacrifice of thousands every day. Immobilized, the only sane man in an insane universe stuck in perpetuity.
Sighing, he then sank to his knees for hours as his sons arrived. Guilliman, Johnson, Khan, and Perturabo. An alliance of demigods, consoling the broken God whose tears wept for the future he had envisioned, and in recognition of the future that would be. After a couple of hours, the Emperor rose and turned to his sons.
"I expected that I would die in the battle with my son the Warmaster. That in death I would serve the Imperium for ten millennia until this device failed and I sank to death, a species failed."
He pointed to the place where the psychic residue of Malcador remained.
"Before he died, I told Malcador to prepare for the future. One unbreakable shield against the coming darkness. One last blade forged in defiance of fate. A legacy to the Galaxy I conquered, and one last gift to the species I failed. Then I expected to die, and now because of the strangeness of fate," and he here he looked to Perturabo with a strange gaze that mixed sorrow and wonder, "I live."
He stood up and told them, "My sons, the Imperial Truth has failed spectacularly. Much as it pains me, I must endorse the very words of Lorgar, and make them a truth to unify humanity. No longer their Emperor," he sighed deeply, "now a God-Emperor in Holy Terrra, assailing my foes as needs be. This Heresy has broken my initial weapons."
He rubbed his face with his armored gauntlet, another deep sigh issuing from seemingly within his soul. For a moment the ageless giant seemed very old indeed and weighed down with the pressures and weight of all those years. The moment passed.
"The battle on the Vengeful Spirit will lead the traitors to flee into the Eye of Terror. Though it may defy conventional strategy, I shall let my traitorous sons and Astartes flee. We have lost so much on Terra that must be rebuilt first." The Emperor sighed.
"Malcador sealed the Warp-Rift in Terra, and paid for that with the ruin of his life and body." He looked to his sons.
"Today is the first day of a new era. The age of enlightenment and empirical truth has ended, my sons. Now we face the age of darkness, where there is nothing among the stars but slaughter and the thirst of laughing gods. My first aim to destroy Chaos has failed. It may be that this second one will also fail over the course of the Long War."
His sons, now with the rest of his Primarchs, his loyal ones, who still lived and who'd arrived and straggled in, appalled at the detritus of the battle before and around them gathered around him as he raised his sword and they all raised their weapons.
"We may not be able to defy fate," the God-Emperor vowed, "but we shall give the Ruinous Powers such a death of the human race that they shall tremble in their Hells. And perhaps, if the first approach failed, that second shall succeed. To the glory of the human race!"
The Primarchs as one shouted, "To the glory of the human race!"