'My brother,' he whispered, 'my friend.'

'You have long since lost the right to call me friend,' snarled Ferrus, pushing himself to his feet and staggering towards Fulgrim with Fireblade raised to smite him.

Fulgrim cried out, and his hand leapt unbidden to his waist as the flaming blade carved a burning path towards his neck. Silver steel flashed as he drew the sword he had taken from the Laer temple and blocked the descending weapon. Ferrus's sword hissed and spat as it bit into the silver blade, the Primarch of the Iron Hands' strength forcing the blazing metal, centimetre by centimetre, towards Fulgrim's face.

'No!' cried Fulgrim. 'This is not right!'

The amethyst stone at the hilt of Fulgrim's sword pulsed with an evil light, bathing Ferrus Manus's face in a leering purple glare. Energy streamed from the blade, and musky smoke billowed around them, deadening sounds and obscuring sight. Fulgrim felt a monstrous presence swell around him, its power and nameless essence more intoxicating and dreadful than anything he could ever have imagined.

Diabolical strength flooded his limbs and he pushed against the power of Ferrus Manus, feeling his brother's surprise at his resistance. With a cry of animal rage, he surged to his feet and hurled Ferrus Manus back, spinning and lashing out with his sword.

The silver edge bit deep into the breastplate of his brother's armour, and the Primarch of the Iron Hands cried out, falling to his knees once again as the blade's flaring energies parted his dark armour like a fingernail through cold grease. Hot blood sprayed from the wound and Fireblade slid from Ferrus's hand as he gasped in fierce agony.

Finish him! Kill him! the voice screamed, and to Fulgrim it seemed as though it echoed across time and space as well as within his skull. He staggered with the blunt force of its imperative, lurching as though his limbs were not his to control.

His normal grace and elan were forsaken as he falteringly raised the silver sword in preparation of delivering the deathblow to Ferrus Manus. Unknown energies coruscated along the notched blade and down the length of his arms into the meat and bone of his wounded body.

Fulgrim was wreathed in purple fire. Crackling arcs of lightning caressed him with a lover's tenderness, seeking out his open wounds and licking them with balefire as they sought entry to his flesh.

Fulgrim stood above Ferrus Manus, his chest heaving convulsively as his entire body shook with the violence of the power that sought to claim him.

He must die! Otherwise he will kill you!

Fulgrim looked down at his defeated opponent and saw his own reflection in the mirrors of Ferrus's eyes.

In an instant that stretched for an eternity, he saw what he had become and what monstrous betrayal he had allowed himself to be party to. He knew in that eternal moment that he had made a terrible mistake in drawing the sword from the Laer temple, and he fought to release the damnable blade that had brought him so low.

His grip was locked onto the weapon and even as he recognised how far he had fallen, he knew that he had come too far to stop, the realisation coupled with the knowledge that everything he had striven for had been a lie.

As though moving in slow motion, Fulgrim saw Ferrus Manus reaching for his fallen sword, his fingers closing around the wire-wound grip, the flames leaping once more to the blade at its creator's touch.

Kill him before he kills you! NOW!

Fulgrim's blade seemed to move with a life of its own, but it had no need of such impellents, for he swung the blade of his own volition.

The silver blade clove the air as it swept towards Ferrus Manus, and Fulgrim felt the ancient triumph of the presence that he now knew had dwelt within it all this time. He tried desperately to pull the blow, but his muscles were no longer his own to control.

Unnatural warp-forged steel met the iron flesh of a primarch, its aberrant edge cutting through Ferrus's skin, muscle and bone with a shrieking howl that echoed in realms beyond those knowable to mortals.

Blood and the monumental energies bound within the meat and gristle of one of the Emperor's sons erupted from the wound, and Fulgrim fell back as the searing powers blinded him, dropping the silver sword at his side. He heard a shrieking wail, as of a choir of banshees, whip around him as phantom, skeletal hands clawed at him, and a thousand voices tore at his mind.

Ghostly whirlwinds seized him and spun him around, twisting him like a limp rag in their grip, and threatening to tear him limb from limb in retribution. Even as he welcomed such oblivion, he felt another presence move to protect him, the same presence that had guided his sword arm, the same presence that had been his constant companion since Laeran, though he had not known it.

Fulgrim fell to the ground as the winds released him, and faded with a shrieking howl of anguished frustration. He landed heavily and rolled onto his side, heaving great gulps of cold air into his lungs as the sound of battle returned to him. He heard cries of pain, gunfire, explosions and the rhythmic crack of bolters as they fired relentless volley after volley. It was the sound of death.

It was the sound of a massacre.

His entire body aching with pain and loss, Fulgrim pushed himself upright. Blood and the detritus of battle surrounded him, the stoic figures of armoured warriors staring in wonder at the headless body that lay-on the black ground before him.

Fulgrim took a shuddering breath and raised his hands to the heavens, screaming his loss at the sight of his brother so cruelly murdered.

'What have I done?' he howled. 'Throne save me, what have I done?'

What needed to be done.

Fulgrim heard the voice as a sibilant whisper in his ear, the breath of the speaker hot on his neck. He twisted his neck, but there was nothing to be seen, no unseen speaker or mysterious presence.

'He's dead,' whispered Fulgrim, the aching loss and guilt of his crime too monstrous to believe. 'I killed him.'

Yes, you did. With your own hands, you struck down your brother, he who had only thought well of you and fought faithfully with you through all the long years.

'He… he was my brother.'

He was, and all he ever did was honour you. The looming presence that surrounded him and spoke to him seemed to claw at his eyes with insubstantial fingers, and Fulgrim felt his mind wrenched into the realm of memory, seeing once again the battle against the Diasporex and the Fist of Iron coming to the rescue of the Firebird. He saw the resentment he had picked at for months, only now understanding the altruism of Ferrus Manus's deed and the loss of life his selfless act had incurred. Where before he had seen only self-aggrandisement in his brother's action, he now saw it for the heroic deed it had truly been.

His brother's critical comments, the wounding darts meant to undermine him, he now saw had been jests designed to puncture his self-importance and restore his humility. What he had perceived as Ferrus's prideful boasts and rash actions had been deeds of courage that he had spitefully dismissed.

Ferms's rejection of his attempt to betray him was the act of a true friend, but only now did he see how his brother had, even then, tried to save him.

'No, no, no,' wept Fulgrim as the true horror of what he had done struck him with the force of a thunderbolt. He looked around through tear-filled eyes and saw the horrific changes wrought upon his beloved Legion, the perversions that masqueraded as epicurean pleasure.

'Everything I have done is ashes,' he whispered and swept up the golden Fireblade, so recently wielded by his brother in an attempt to undo the evil Fulgrim had embraced.