He still carried the great musical instrument he had taken from Bequa Kynska's orchestra, modified to bear spiked handles and grips to render it into a terrifying sonic weapon. Together, he and his fellows unleashed a barrage of discordant scales that sent a dozen of the Morlocks into convulsions, and Julius screamed his appreciation as he leapt to meet Gabriel Santar with his sword aimed at his throat.

The horror of what he was seeing almost cost Gabriel Santar his life. The Emperor's Children before him were like nothing he could ever have imagined in his worst nightmares. Though the enemies he had fought before had been honourless traitors, at least they had still been recognisable as Astartes. These were degenerate perversions of that perfect ideal: warped and twisted freaks who openly displayed their perversions.

A mutilated monster in power armour draped with bloody flaps of skin shrieked as he swept some bizarre weapon back and forth, its deadly sonic energies tearing warriors apart in explosions of ruptured armour and liquefied flesh.

Even as Santar raised his energised fist to block a sword cut aimed at his head, he recognised the twisted features of Julius Kaesoron. The warrior was a thrashing dervish, laughing and howling as he spun like a lunatic around Santar, slashing wildly as he attacked. Kaesoron's weapon was a fearsome, energised glaive that was easily capable of carving through his armour, and Santar turned as fast as he was able to block each ferocious stroke of the blade, but even one as fast as he could not hope to match his opponent's serpent-like speed.

He caught the descending blade of his opponent's weapon between the digits of his energy wreathed fist and a fiery explosion burst between them. He twisted his wrist, and Julius's blade snapped, leaving only the length of a forearm above the quillons.

Santar grunted in pain as he felt the skin of his fist fuse with the melted plates around his hand. He saw Julius sprawled on his back, the ceramite armour of his breastplate bubbling with the residue of the explosion, his face a screaming, burnt horror of seared flesh and exposed bone.

Despite the pain of his burned claw of a hand, Santar grinned beneath his helmet and stomped forwards to deliver the avenging deathblow to his hated enemy. He raised his foot to stamp down on Julius's chest, the power of his Terminator armour easily able to crush Astartes plate.

Then he saw that Julius wasn't screaming in pain, but in orgasmic pleasure.

He paused in revulsion for the briefest second, but that second was all that Julius needed. Sweeping up the broken edge of his glaive, the blade alive with flaring energies, he rammed it into Santar's groin.

The pain was unimaginable, surging agonisingly around his body. Julius Kaesoron tore the remains of the weapon upward, molten gobbets of armour dropping to the dark sand in the midst of a spraying rain of Santar's blood. The blade tore through his pubis and ripped into his breastplate as Julius rose to his feet with the motion of his sawing weapon.

Santar's entire body convulsed in agony, not even the frantically pumping pain balms able to mask the horrifying agony of having his torso carved open. He tried to move, but his armour was locked in place as Julius looked directly at him. His face was horrifically illuminated in the firelight of the battle, the skin peeled away from the musculature beneath, and the while gleam of bone jutting through his cheeks.

Even amid the thunder of battle and with his lips burned away, Julius's next words were horribly clear to Santar as his life slipped away.

'Thank you,' gurgled Julius. 'That was exquisite.'

The battlefield of Isstvan V was a slaughterhouse of epic proportions. Treacherous warriors twisted by hatred fought their once-brothers in a conflict unparalleled in its bitterness. Mighty gods walked the planet's surface and death followed in their wake. The blood of heroes and traitors flowed in rivers, and hooded adepts of the Dark Mechanicum unleashed perversions of ancient technology stolen from the Auretian Technocracy to wreak bloody havoc amongst the loyalists.

All across the Urgall Depression, hundreds were dying with every passing second, the promise of inevitable death a pall of darkness that hung over every warrior. The traitor forces were holding, but their line was bending beneath the fury of the loyalist assault. It would take only the smallest twists of fate for it to break.

And then they came.

Like fiery comets from the heavens, the thrasters of countless drop-ships, landers and assault craft broke through the fire-shot clouds of smoke and descended to the loyalist landing zone on the northern edge of the Urgall Depression. Hundreds of Stormbirds and Thunderhawks roared towards the surface, their armoured hulls gleaming as the power of another four Legions came to Isstvan, their heroic names legendary, their mighty deeds known the length and breadth of the galaxy: Alpha Legion, Word Bearers, Night Lords, Iron Warriors.

Ferrus Manus smote all around with his fists, twin balls of silver steel that crushed bone and clove armour wherever they struck. His gun was discarded, his load of ammunition long since expended, but he needed no mere weapon to be a lethal killing machine. No blade could wound him and no shot could penetrate his armour, his every movement a fluid economy of motion as he killed with every stride, pushing the fighting wedge of the Morlocks deeper into the traitor lines.

The sword at his waist hung like a lead weight of cosmic justice at his side, but he would not draw it, not until he faced his traitorous brother and revealed its terrible purpose before taking his revenge.

He longed to push ahead of his warriors, to carve a bloody path through the traitors in search of Fulgrim, but while the battle still hung in the balance he could not set aside his duty of command, and seek a duel with the viperous primarch to settle once and for all the enmity between them.

The fire and clamour of war surrounded him. Smoke boiled from wrecked tanks and shattered defences, and explosions of gunfire filled the air with bullets, bolts and lasers. Screams and blood filled his senses, the chaotic nature of the battlefield a morass of thousands upon thousands of warring Astartes. Even through his fury, Ferrus saw the horrific tragedy being played out upon the stage of Isstvan V. Nothing would ever be the same again after this battle, even in their final victory.

This betrayal would stain forever the honour of the Astartes, no matter the outcome.

Men will fear us from this day onwards, and they will be right to, thought Ferrus.

He heard the cries of jubilation behind him, but it was some moments before their substance penetrated his killing rage. He crashed the skull of a warrior of the Sons of Horus in his mighty fist and turned to see the welcome sight of an aerial armada of gunships dropping from orbit.

'My brothers!' he yelled triumphantly as he recognised the familiar iconography of his fellow loyalists. Alpha Legion Thunderhawks screamed over the battlefield, and the midnight-skinned vessels of the Night Lords swooped in to take position on the flanks to envelop the Warmaster's forces. Word Bearer Stormbirds howled in on screaming jets, the gold wings on the glacis of their craft shimmering as though afire in the glow of battle. Heavy transports of the Iron Warriors slammed into the Urgall Depression and disgorged thousands of warriors, who immediately began fortifying the landing zones with armoured barricades and looping coils of razor wire.

Tens of thousands of his fellow Astartes poured onto the surface of Isstvan V, and in a single stroke, the loyalist force was more than doubled in size. Ferrus punched the air in righteous vindication as he watched the power and might of his brothers' Legions fill the black desert behind him, their warriors, fresh meat for the battle.