'It is fitting we face one another with the weapons we forged long ago,' said Fulgrim.

'I have long waited for this moment, Fulgrim,' replied Ferrus, 'ever since you came to me with betrayal in your heart. For months I have dreamt of this reckoning. Only one of us will walk away from this, you know that.'

'I know that,' agreed Fulgrim.

'You betrayed the Emperor and you betrayed me,' said Ferrus, and Fulgrim was surprised to hear genuine emotion in his brother's voice.

'I came to you because of our friendship, not despite it,' answered Fulgrim. 'The universe is changing, the old order upset and a new dawn approaching. I offered you the chance to be part of the new order, but you threw it back at me.'

'You sought to make me a traitor!' snarled Ferrus. 'Horus is mad. Look at all this death! How can this be right? You will hang from Traitor's Gibbet for this sedition, for I am the Emperor's loyal servant and through me his will and vengeance will be done.'

'The Emperor is a spent force,' snapped Fulgrim. 'Even now he whittles away on some trivia in the dungeons of Terra while his realm is in flames. Are those the actions of a being fit to rule the galaxy?'

'Do not think you can win me to your cause, Fulgrim. You failed once and you will not get a second chance.'

Fulgrim shook his head. 'I am not offering you a second chance, Ferrus. It is already too late for you and your warriors.'

Ferrus laughed at him, but he could sense the despair in it. 'Are you mad, Fulgrim? It's over. You and the Warmaster are defeated. Your forces are routed and the power of another four Legions will soon crush your attempt at rebellion utterly.'

Fulgrim was unable to keep the sensations seething in his head contained any longer and he shook his head as he savoured his next words. 'My brother, how naive you are. Do you really think Horus would be foolish enough to trap himself like this? Look to the north and you will see that it is you who are undone.'

The forces of the Raven Guard and Salamanders fell back in good order to the drop zone, where their reinforcements were deploying to join the fight. The drop-ships of the Iron Warriors, armoured bastions connected by high walls of spiked barricades, formed an unbroken line of grim fortifications on the northern slopes of the Urgall Depression.

A force larger than that which had first begun the assault on Isstvan mustered in the landing zone, armed and ready for battle, unbloodied and fresh.

Corax and Vulkan led their forces back to regroup and to allow the warriors of their brother primarchs a measure of the glory in defeating Horus, dragging their wounded and dead with them. The victory had been won, but the cost had been steep indeed, with thousands of all three Legions lost to the betrayal of the Warmaster. Horus's forces were in retreat, but there would be no celebration of the slaughter, no joyous victory feasts or glorious days of remembrance, only another sad scroll added to a banner that would never again see the light of day.

Scorched tanks rumbled alongside the Astartes, their ammunition expended and their hulls battered by the impact of shot and shell.

Unanswered vox hails requested medical aid and supply, but the line of Astartes at the top of the north ridge was grimly silent as the exhausted warriors of the Raven Guard and Salamanders came to within a hundred metres of their allies.

A lone flare shot skyward from inside the black fortress where Horus had made his lair, exploding in a hellish red glow that lit the battlefield below like a madman's vision of the end of the world.

And the fire of betrayal roared from the barrels of a thousand guns.

Fulgrim laughed at the stunned look on Ferrus's face as the forces of his ''allies'' opened fire upon the Salamanders and Raven Guard. Hundreds died in the fury of the first moments, hundreds more in the seconds following, as volley after volley of bolter fire and missiles scythed through their unsuspecting ranks. Explosions flashed to life in their midst, vaporising warriors and tearing through tanks as the force of four Legions ripped the beating heart from the first wave of loyalists.

Ferrus Manus watched in mute horror as he saw a storm of fire engulf Corax, and a titanic explosion mushroom skyward from where Vulkan stood in astonished outrage at what was happening.

Even as terrifying carnage was being wreaked upon the loyalists below, the retreating forces of the Warmaster turned and brought their weapons to bear on the enemy warriors within their midst. Hundreds of World Eaters, Sons of Horus and the Death Guard fell upon the veteran companies of the Iron Hands, and though the warriors of the X Legion continued to fight gallantly, they were hopelessly outnumbered and would soon be hacked to pieces.

Ferrus Manus turned to face Fulgrim, and the Primarch of the Emperor's Children could see the despair etched into his brother's features, his silver eyes dull and lifeless. To have so great a victory snatched away in an instant must be the most sublime sensation. Fulgrim almost wished to switch places with his brother just to taste that feeling for himself.

'Only dismal defeat and death await you, Ferrus,' said Fulgrim. 'Horus has commanded your death, but for the sake of our past friendship I shall plead your case to him if you throw down your arms. You have to surrender, Ferrus. There is no escape.'

Ferrus Manus tore his eyes from the slaughter of the loyalist forces, his teeth bared with the volcanic fury of his home world.

'Maybe not, traitor, but only dishonour holds any terror for me,' spat Ferrus. 'The Emperor's loyal warriors will not surrender to you, not now, not ever. You will have to kill every last one of us!'

'So be it,' said Fulgrim, launching himself towards Ferrus Manus, swinging his mighty warhammer. The primarchs' weapons, forged in brotherhood, but wielded in vengeance, met in a blazing plume of energy, and the battlefield was illuminated for hundreds of metres by their ferocious energies.

The two primarchs traded blows with their monstrously powerful weapons, the strength to defeat armies and topple mountains unleashed as they fought like gods forced to end their dispute in the realm of mortals. Ferrus Manus wielded his flaming blade in fiery slashes, his every blow defeated by the ebony hafted hammer he had borne in countless campaigns.

Fulgrim swung his hammer in great, looping arcs, its heavy head powerful enough to crush the armour of a Titan to paste. Both warriors fought with the hatred only brothers divided can muster, their armour dented, torn and blackened by the fury of their conflict.

To fight an opponent of such magnificence was a privilege, and Fulgrim savoured every clash of hammer and sword, every fiery line cut across his flesh and every grunt of pain torn from his brother's mouth as Forgebreaker glanced his armour. They circled in the midst of cries of pain and roaring savage glee, the Morlocks of Ferrus Manus slain, but for a last few desperate heroes.

Ferrus cut the shoulder guard from Fulgrim's armour and spun inside his guard to deliver a lethal thrust towards his groin. Fulgrim stepped to meet the blow, batting aside the tip of the fiery sword with the haft of Forgebreaker, and hammering the warham-mer's head towards Ferrus's skull.

The Primarch of the Iron Hands took the blow, dropping to one knee and lashing out with his blade as blood streamed from the terrible wound in his temple. The sword's fiery tip cut across Fulgrim's stomach, opening his armour and tearing through his flesh. The pain was indescribable, and Fulgrim fell back, dropping his hammer as his hands sought to stem the blood pouring from his body.

Both primarchs faced each other on their knees through a haze of pain and blood, and Fulgrim once again felt an ache of sadness well within him. The pain of his wounds, and the sight of his brother's broken skull coated in blood, tore a window into his mind. The sensation was like a powerful gust of fresh mountain air, clearing away the fog that had wrapped him in a suffocating embrace for so long that he no longer noticed it until it was gone.