Taken from the text of the Sage Alexander Petranus, who observed the battle via a holoprojecter set in the Inquisitorial Battle Barge

The Marines of the Oathkeepers descended upon the burning city, their bolters singing the praises of the Emperor. Isaiah Aetos led the charge, his famous blade shining in his hand. With him flew Octavius Drakonis, that unparalleled man whose very presence could send an entire regiment of Julian's foul traitors into flight. On the right flank stood Claudius Varnus, that hardened Chaplain, with a sixteen picked men who had vowed to either find Julian's head or perish in the attempt. And who could forget the blessed Canoness, Clara Amparion, who flew with six of her heavenly Seraphim. Isaiah had begged her to stay behind until the city was secure, but the holy sister thirsted for vengeance against those who had betrayed mankind. Together, these four champions charged into the citadel of the betrayer, ready to claim the Apostate Governor once and for all.

Though the Governor's dupes were well fortified, the Marines moved from house to house, slaying everyone they could find before moving onward. As the final assault upon the Governor's Palace began, the foul traitors of the Alpha Legion revealed themselves at last. As Isaiah and Octavius forced their way into the Governor's ruined palace, there was a great explosion. From the smoke came a towering figure. His eyes glowed red with blood and he held a massive scythe aloft.

"Welcome Captain," the Arch-Traitor said as he brandished his weapon and licked his lips with a forked tongue, "Allow me to introduce myself... I am Caine. I trust that my Guardsmen have been good company. I must say, your Governor has been a wonderful puppet. I have seen your skill, Captain, and I do say that you will be a worthy replacement. So I will give you this chance now: Bow before me and call me master and you may yet be spared."

"So," Octavius said softly, with holy lightning twisting around his Force Weapon, "It was your whispers that drove the Governor into madness. Your whispers which damned this world."

"The Gods of Chaos whisper in the hearts of all men, brothers," Caine declared, his twisted mouth attempting to smile, "You foolish Loyalists are simply too weak to hear their call."

"Then feel the wrath of those you call weak," Isaiah declared, raising his sword high, "For the Emperor!"

And with His name upon their lips, the Loyalists charged. Isaiah and Caine's blades clashed, the scythe's dark blade deflecting Isaiah's holy sword before bouncing off the holy shield of the Brother Captain's Iron Halo. Octavius came forward then, his flaming staff striking home and forcing the blasphemous Champion back. Caine screamed and a killing blow from his scythe sailed towards the Librarian's head. It was not an inch away from Octavius' armour when Yoz, his faithful familiar, flew forward.

"Yoz!" Octavius cried as his oldest friend was cut in two by the black scythe.

Isaiah sprang forward, taking advantage of Caine's moment of elation. He struck a firm blow against the foul Traitor's skull and then activated his jump pack. Power armour struck power armour as Caine screamed, arms pinned against the wall by the strength of Aetos' jump pack.

"Octavius! Finish it!"

Octavius, still feeling the sting of his loss, brought his staff down and sundered black power armour. A second passed where the Librarian looked the Arch-Betrayer in the eye before holy thunder shook the building. Isaiah leapt away as Caine's armour was set aflame by righteous fury. The traitor writhed on the ground and screamed before a flash of light blinded everyone in the room. When the storm passed, all that was left of Caine was a pile of ash.

"Well done, Brother," Isaiah said as he took a moment to catch his breath, "But wait... where is Clara?"

Octavius was silent for a moment and his eyes appeared distant. "She has gone ahead of us... Claudius is with her and... by the Emperor... we must hurry!"

The Brothers flew through the narrow corridors. The few Renegades that offered resistance were cut down as the Assault Marines found their way to the blood-soaked throne room. The scene they witnessed I shall never forget... at one side of the room stood Julian upon a raised dais, a host of traitor Marines, Daemons and Renegades all around him. At the other stood Clara, the Chaplain Claudius and a handful of Marines, their backs to the wall as a massive Daemonic abomination cut through their ranks. It's great cleaver swung downward, knocking Claudius off his feet and across the room. He slammed against the wall and crashed to the ground, limp. It turned back towards the Canoness, grinning toothily.

"Clara!" Isaiah cried as she narrowly dodged the monstrous Daemon's cleaver.

There was a sickening laugh. "Where is your Emperor now, girl?" Julian sneered from his throne, "Your Marines have failed you, but it is not too late to beg for my mercy. I assure you, your death will be quick."

"You will pay for all the blood you have spilled, swine!" Clara snarled, "I shall avenge my sisters and my world here and now!"

With that declaration, the Daughter of the Emperor sprang upward, her jump pack carrying her above the throng as lasgun fire deflected off her power armour. She was but an inch from Julian when a blue whip struck like lightning. It wrapped around her waist and pulled her down to earth. "Well done, Vross," Julian said as the whip retracted and wrapped around her throat, "I'm sorry Clara. Be certain to tell your Emperor that he shall see me before long."

A spark of blue light coursed through the whip and the holy martyr fell limp. "Clara!" Isaiah yelled, "Clara! No!" He charged forward, only to have the massive cleaver of the Greater Daemon block his advance. Octavius dodged to his right and struck the foul beast's tainted flesh vainly.

"Fools!" Julian yelled as the forces of Chaos moved in for the kill, "The Gods of Chaos cannot be denied! Not by you, not by the Orks or that fool Sarados! He thought me weak, but the Gods stand with me! And soon the entire galaxy shall come to know my name!"

"The only thing that shall be remembered is your folly."

For a moment, all was silent. Daemon and human, loyalist and traitor alike stood still, eyes searching out the source of the sound. From the corner of the room, five shining figures emerged, their swords glowing blue. The Greater Daemon screamed, his cleaver falling to ground and his massive arms clasping at his head. It pounded a fist into the wall and opened a hole before running through the opening.

"Governor Julian," said Grandmaster Lucas, "By the authority of the God-Emperor of mankind, I find you guilty of treason. Face my judgement."

"Who... who dares? St... Stop that man!"

The Grey Knights advanced in a walk. Renegades and Alpha Legion Marines fell in droves as the greatest of the Emperor's servants charged, singing His holy names as they cut through flesh and armour alike. Lucas eyes remained locked upon the Ex-Governor, walking up the steps to the throne with his ancient blade at the ready. The one called Vross sprung forward to halt him, but his whip was sliced in two by a simple flick of Lucas' wrist. Glancing at his master briefly, Vross threw down his weapon and ran without speaking a word.

Lucas continued his ascent. Julian shook visibly and fired twice with his pistol at that giant of a man, only to have the shots bounce harmlessly off his ancient armour. Julian raised his blade high and lowered it, faster than the eye could see. The Governor crumpled.

"So," Julian gasped, "The Emperor's help comes at long last."

"The Emperor's light can never be denied, traitor," Lucas said as he withdrew his blade.

"Be that as it may," Julian replied, "I saved this world... the people... will remember me... I..."

The Grandmaster turned his back as Julian breathed his last breath. A great scream was taken up by the Renegades then. Seeing their leader dead, they fled, even as the Grey Knights continued their slaughter. The surviving Alpha Legion Marines, seeing the day lost, began to fire their bolters anew as they moved backwards in a fighting retreat. The Grandmaster, always remembering his duty, followed after them.

Octavius walked towards his Captain as his squad made to join the pursuit. His Captain was kneeling near the throne next to Clara's limp body. The jolt of the whip had not left a mark on her body. The Brother-Captain placed an armoured hand upon her face and gently shut her eyes.

"Brother Captain... Claudius is still alive," Octavius said quietly, "He needs to be brought to the apothecaries immediately."

The Brother-Captain was silent.

"She died with the Emperor's name on her lips. She died saving this planet from heresy. We must not dishonour her sacrifice, Isaiah."

"No," Isaiah said softly. He looked down at the Sister for the final time, "May the Emperor always smile upon you, his finest daughter."