His vox-unit chimed urgently as a ripple of fear visibly passed along the traitor lines at the sight of such a terrifying display of martial power. His practiced eye could see that the traitor forces had lost their stomach for the slaughter, entire cohorts pulling back from their prepared positions in dismay. Even the Dies Irae was retreating, the mighty Titan cowed in the face of such overwhelming force.

Ferrus saw the distant form of Mortarion ushering his warriors back towards the rained fortress, and even Angron was retreating, his bloodstained World Eaters like some monstrous, bloody tribe of head-hunters. But the Emperor's Children…

The smoke parted before him, and Ferrus saw what he had been looking for ever since he had set foot on this damned planet.

Clad in shimmering armour of purple and gold, he saw Fulgrim.

His former brother drew his most debased followers to him, waving them back to the black walls with long sweeps of a glittering silver blade. A long haft of ebony, worked with silver and gold extended behind his shoulder, and Ferrus smiled grimly as he realised that his brother had also understood that the fates had ordained this duel must take place upon the blasted plain of Isstvan V.

Twisted freaks in flesh-covered armour surrounded the Primarch of the Emperor's Children, and a monster with red, seared flesh attended at his right hand. Only now, at the end, did Fulgrim dare to reveal himself.

Even as Ferrus finally saw Fulgrim, he knew that his brother too was aware of him. He felt hate and betrayal rise in him like a suffocating wave.

The traitors were falling back from the loyalists with increasing speed, leaving thousands of corpses behind them, both friend and foe. The scale of the slaughter was not lost on Ferrus, and though his blood sang with this victory and his imminent confrontation with Fulgrim, he was not blind to the fact that the loyalist Legions had suffered appalling casualties to win it.

He watched the enemy line melt before him, the loyalist warriors exhausted by the furious battle, stumbling as their enemy fled before them. He called his Morlocks to him before opening a channel to Corax and Vulkan.

'The enemy is beaten!' he shouted. 'See how they run from us! Now we push on, let none escape our vengeance!'

Grainy static washed through the reply, Corax's words almost lost amid the rambling thunder of explosions and the descent of yet more allied drop-ships.

'Hold, Ferrus! The victory may yet be ours, but let our allies earn their share of honour in this battle. We have achieved a great victory, but not without cost. My Legion is bloodied and torn, as is Vulkan's. I cannot imagine yours has not shed a great deal of blood to carry us this far.'

'We are bloodied, but unbowed,' snarled Ferrus, watching as the distant figure of the fabulously bedecked Fulgrim climbed to the top of a jagged spur of black rock and spread his arms in blatant challenge. Even from hundreds of metres away, the mocking smile twisting his features was clearly visible.

'As are we all,' put in Vulkan. 'We should take a moment to catch our breath and bind our wounds before again diving headlong into such a terrible battle. We must consolidate what we have won and let our newly arrived brothers continue the fight while we regroup.'

'No!' shouted Ferrus. 'The traitors are beaten and all it will take is one final push to destroy them utterly!'

'Ferrus,' warned Corax, 'do not do anything foolish! We have already won!'

Ferrus snapped off the vox-channel and turned to face the surviving Morlocks of his bodyguard. A half century of Terminators surrounded him, their clawed gauntlets crackling with blue arcs of energy and their proud stances telling him they would follow whatever order he gave, whether it be to retreat or to march into the hell of battle once more.

'Let our brothers rest and lick their wounds!' he yelled. 'The Iron Hands will let no others have the satisfaction of settling our affairs with the Emperor's Children!'

Fulgrim smiled as Ferrus Manus renewed his attack into the heart of the defensive lines atop the Urgall Depression. Backlit by the flaring strobe of battle, his brother was a magnificent figure of vengeance, his silver hands and eyes reflecting the fires of slaughter with a brilliant gleam. For the briefest second, Fulgrim had been sure that Ferrus would pause to muster with the Raven Guard and Salamanders, but after his daring challenge atop the rock, there would be no restraining his brother.

Around him, the last of the Phoenix Guard awaited the blunt wedge of the Iron Hands, their golden halberds held low and aimed towards their foes. Marius and his wailing sonic weapon howled in anticipation of the combat, and Julius, almost unrecognisable with his skin burnt from his bones, ran a blistered tongue around the lipless ruin of his mouth.

Ferrus Manus and his Morlocks charged through the shattered ruin of the defences, his black armour and their burnished plates scarred and stained with the blood of enemies. Fulgrim's fixed smile faltered as he truly appreciated the depths of hatred his brother held for him and wondered again how they had come to this point, knowing that any chance for brotherhood was lost.

Only in death could this end.

The retreat of the Warmaster's forces appeared ragged and faltering, exactly as Horus had planned it. Warriors streamed back from the front lines of battle in determined groups, their spirits apparently broken, but gathering in knots of resistance behind shelled ruins and fire-blackened craters.

The Iron Hands pushed through the defences, the bulky Terminators unstoppable in their relentless advance. Lightning crackled from the claws of their gauntlets and their red eyes shone with anger. The Phoenix Guard braced themselves to meet the charge, fully aware of the power of such mighty suits of armour.

Marius released a howl of ecstatic joy, and his bizarre weapon amplified it into a screeching wail of deadly harmonics that ripped through the ground in a roaring sonic wave to explode amongst the front ranks of the Morlocks.

The giant warriors were torn apart in a clashing shriek of aural power as the apocalyptic noise made play of their armour and butter of their flesh. The Emperor's Children screamed in pleasure at the sound, their enhanced senses and augmented brain paths rendering the discordant sounds into the most vivid sensations imaginable.

'When they come,' shouted Fulgrim, 'leave Ferrus Manus to me!'

The Phoenix Guard answered with a terrible war cry and leapt to meet the Morlocks in a searing clash of blades. Electric fire leapt from the golden edges of the halberds and claws of the warriors, and a storm of light and sound flared from each life and death struggle. The battle engulfed the Primarch of the Emperor's Children, but he stood above it, awaiting the dark armoured giant who strode inviolate through the lightning shot carnage as brothers hacked at one another in hatred.

Fulgrim nodded in greeting as Ferrus reached towards a sword belted at his waist, and he smiled as he recognised Fireblade's hilt.

'You remade my sword,' said Fulgrim, his voice cutting through the atrocious din of fighting. Though the ferocious battle between the Morlocks and the Phoenix Guard surrounded them, neither primarch's praetorians dared approach them, as though aware that to transgress this fateful confrontation would be a heinous crime.

'Only to see you dead by a weapon forged by my own hand,' spat Ferrus.

In response, Fulgrim sheathed his silver sword and reached behind him to unlimber the great warhammer held at his back. 'Then I shall do likewise.'

The great weight of Forgebreaker, the weapon his own skill and energies had crafted beneath the peaks of Mount Narodnya, felt good in his hands as he descended the rock to face his erstwhile brother.