'Obax Zakayo!' screamed a voice, but Uriel could not see who shouted through the pain screeching around his nervous system. Gunshots burst against the Iron Warrior's armour and he lashed out with his axe.

'You?' laughed the Iron Warrior. 'You were under my blade once, slave, and escaped. You will not do so again.'

For the briefest second, his attention shifted from Uriel and it was all the distraction he needed. He swept up his sword, hacking through the energy whip, and the pain vanished, leaving him drained, but free of its incapacitating agony. Uriel pushed himself to his feet, seeing Colonel Leonid and Sergeant Ellard facing off against the Iron Warrior.

Lasbolts hammered his bulky body, but his debased power armour could withstand such trifles and he roared, swinging his axe for Leonid's midriff. The colonel jumped back, stumbling on loose rubble, and fell to the ground. Obax Zakayo closed for the kill, but Ellard leapt upon the Iron Warrior, pummelling his fists against his head.

Ellard was a big man, but next to the Iron Warrior he was a child, and Obax Zakayo ripped him from his back and hurled him away. Uriel stepped in and hammered his sword across the Iron Warrior's shoulders. The blade crackled as it hacked though the ceramite plates of his armour, but slid free before connecting with flesh.

Obax Zakayo swung his axe in a vicious arc at Uriel's groin, but the blow never landed as the ground shook and cracked, molten metal spewing up as the crashing footsteps of the battling Titans finally split the mountain. White hot metal hissed and spat as it spilled out onto the rocks, rendering them down to slag in seconds. Uriel scrambled away from the widening crack in the ground, sheathing his sword as he saw that there was no way his opponent could reach him across the gulf of liquid metal.

Roiling clouds of bitter smoke gusted from the river of molten metal and Uriel scrambled away from its intolerable heat, Leonid and Ellard clambering over the rocks to join him.

'This is Uriel Ventris!' he shouted, hoping that the vox-bead attached to his larynx was still functioning. 'If anyone can still hear me, make for the breach above us now!'

Bolters roared behind him and the crash of explosions almost drowned his order, but as he climbed through the blinding clouds of steam and smoke, he could see the shadowy forms of the warrior band climbing towards him.

The breach was above them, barely thirty metres away, the rubble-strewn sides of the fortress a beacon that called him onwards.

They had done it. They had found a way in.

Blood blinded him and a grating static filled his senses. Honsou removed his helmet, tossing it aside in anger, and wiped blood from his eyes. Banks of hot steam sent runnels of moisture down his face and he pushed himself upright as the thunder of battle returned to him with all its fury.

'What in the name of the Dark Gods is happening?' he shouted to no one in particular.

'My lord!' returned Obax Zakayo, picking his way carefully through the rocks. Moisture and blood ran from his armour, his energy whip crackling with sparks where it had been severed. 'The—'

'Renegades!' roared Honsou. 'Is this what Toramino has been reduced to?'

'Aye, renegades,' agreed Obax Zakayo. 'Renegades and runaway slaves, they—'

'I was wrong to fear him, Obax Zakayo,' said Honsou, a measure of calm returning to him. 'They are all dead?'

'No, my lord. The mountain sundered and we were separated.'

Honsou looked up sharply. 'Then where are they?'

'That is what I am trying to tell you. They broke past us and made for the breach!'

'Damn!' cursed Honsou. 'Then why in the name of Chaos are you still standing here?'

'My lord, a river of molten metal separates us. For now, there is no way across.'

'For you, perhaps,' sneered Honsou, striding through the battle to where he had left his trapped champion. 'Onyx!'

Iron Warriors still struggled with the debris that buried the symbiote, but seeing their master's fury and urgency, redoubled their efforts. Within minutes, they had shifted enough of the rubble to allow Onyx to pull himself free of the debris. Lithe, supple and showing no signs of having been almost crushed to death, Onyx made his way gracefully towards Honsou. His black armour bore not a single scratch and Honsou saw Onyx's daemonic powers rippling just below the surface of his crawling, silver-etched skin. His eyes blazed with deadlights as Honsou pointed to the breach.

'Find the renegades,' he ordered Onyx. 'Find them and bring them to me.'

The daemon creature nodded and set off up the slopes of the mountain.

The shattered remnants of this part of the ramparts were eerily deserted, the noise of battle muted from here, as Uriel pulled himself over the tattered lip of stone with the aid of the orange-steel rebars. He rolled to his feet, alert for danger, but finding none. The brooding presence of the fortress still towered above him, but he kept his eyes averted from its monstrous geometries for now, turning and helping the remainder of their force onto the battlements.

The walls swept around the mountain, curving and angled, seemingly at random, hordes of human soldiers and mutants firing from the embattled ramparts into the masses of attackers below. Thousands of warriors fought in the breach, looking from here like some great serpent that heaved and convulsed as it pushed its way, metre by metre, up the rubble slopes.

Pasanius and Vaanes climbed up, followed by Leonid and Ellard and the rest of the warrior band. Uriel could scarce believe it. They were within the walls of the fortress!

'Throne of Terra,' breathed Pasanius. 'That was bloody work!'

'It's not over yet,' cautioned Uriel, turning and more fully surveying their surroundings. A row of great archways led deeper into the fortress, each one as tall as a battle Titan and ringed with grotesque carvings that squirmed within the rock, as though the unquiet matter of the blocks was reshaping itself as they watched.

'Which way?' asked Vaanes as the last of the Space Marines climbed to the ramparts.

'I don't know,' admitted Uriel. 'There is nothing to choose between them.'

'Then we've nothing to lose, whichever one we take,' pointed out Vaanes, heading towards the middle archway.

'I suppose,' said Uriel, though a gut feeling told him that there was something different about this archway. He could not put his finger on what, but since he had no better idea of which one to take, he set off after Vaanes. The Space Marines followed him, bolters levelled in cautious apprehension.

Vaanes waited for him at the entrance to the archway, and as Uriel passed beneath its Stygian immensity, he sketched the sign of the aquila across his chest, hearing a distant pounding, like the slow heartbeat of a sleeping monster.

'We are in the belly of the beast once more, Uriel,' said Pasanius, the guttering blue tip of his flamer throwing their faces into stark relief and causing the carvings on the inner faces of the archway to leer and dance across the walls.

'I know,' nodded Uriel, praying that the white cloak he had put over his soul would protect it from the vile things they were sure to see in the heart of the Enemy's lair.

Onyx ghosted over the lip of the ruined bastion, his bronze claws sliding slowly from his flesh. His silver eyes scanned the battlements for any sign of the renegades, but they were nowhere to be seen. Moving like a shadow, Onyx tasted the air, the crawling silver veins beneath his skin burning brighter as he channelled the daemonic energy within him into tracking the intruders.

His vision shifted into realms of sight beyond the ken of mortal men, where that which had already come to pass could be seen by listening to the echoes in the air. He watched as shadowy forms climbed over the ramparts, in much the same way as he had just done: many warriors, led by one whose soul burned brightly with purpose and another whose soul was withered and dead.