The first of the mutants died with a strangled screech on the point of Uriel's sword, the second fell without a sound as Uriel hacked its head from its body with one blow. Now aware of the killers in their midst, the remainder scattered in terror. A sheet of flame incinerated more of the mutants, their screams ululating as their rubber bodysuits melted on their corrupted flesh.

The slaughter was over in a matter of moments, the twisted mutants no match for the power and fury of the Adeptus Astartes. Most turned to flee, but there was nowhere to hide from Uriel's wrath. As the last mutated creature fell beneath his blade, Uriel took a deep breath, taking profound pleasure in the butchery of such worthless wretches. Whatever deviant beasts they had been in life, they were only so much dead flesh now.

He turned as Pasanius said, 'Uriel, look…' and pointed at the nearest of the skins.

Uriel felt his heart tighten in his chest as he saw the dead features of a man atop the huge expanse of skin. Stretched almost beyond recognition, but a man's nonetheless.

'Holy blood. But how could a man become so vast?' said Pasanius.

Uriel shook his head. 'Not by any natural means.'

'But why?'

'The ways of the Enemy are unknown,' said Uriel. 'Better that some remain so.'

'What shall we do?'

Uriel turned in a circle, seeing row upon row of faces in the skins circling the platform - dead, slack features of men and women staring down at him as though he were the subject in an anatomist's theatre.

'Burn it,' he said. 'Burn it all.'

CHAPTER SIX

With the scorched reek of burning flesh still in their nostrils, Uriel and Pasanius left the depression in the rock, leaving the smouldering remains to the scouring wind and whatever passed for carrion on Medrengard. Invigorated and filled with purpose from the slaying of the mutant things, their step was quick and energised, but by the time they passed through the narrow slice in the rock face and began climbing worn steps carved into the rock, the leaden weight of the daemon world had settled upon them once more.

Uriel glanced back down at the blazing sheets of skin, feeling his hate at what had been done to these people burn as brightly. He knew that the image of the skinned man's features would haunt him forever, and was reminded of the horror of the disassembled flesh sculpture created by the loathsome xeno surgeon beneath the estate of Kasimir de Valtos on Pavonis.

Just by being here he felt polluted, as though his very soul was becoming hardened or being drained from his body to nourish the dead rock underfoot, and he was becoming less himself. The emptiness of Medren-gard was leaving him hollowed out, a shell of his former self.

'What will be left,' he whispered, 'when this world takes the last of me?'

He could tell Pasanius was feeling the same way, his cheeks hollow and his eyes glazed as he trudged up the winding stairs. Even as he watched, Pasanius stumbled, his silver arm reaching out to arrest his fall, but at the last minute his friend snatched his arm back and he fell to his knees instead.

'Are you all right?' asked Uriel.

'Aye,' nodded Pasanius. 'Just hard to keep focussed without an enemy to fight.'

'Fear not, my friend,' said Uriel. 'Once we reach this fortress, I am sure we will have enemies aplenty. If what the Omphalos Daemonium has told us is true, then we will have a surfeit of them.'

'Do you think a daemon of the Skull Lord is capable of telling the truth?'

'I do not know for sure,' said Uriel honestly, 'but I believe daemons only cloak what they need to in lies, wrapping kernels of truth in shrouds of deceit. Part of what it told us is true, I am sure, but which part… well, who knows?'

'So what do we do?' asked Pasanius, trudging after Uriel.

'Whatever we can, my friend,' said Uriel. 'We will act with courage and honour and hope that that is enough.'

'It will need to be,' said Pasanius. 'It is all we have left.'

The hike through the mountains seemed never-ending, their path through the blackened, rocky desolation draining their spirits with every step they took. They saw more of the steam-venting grilles and the acidic reek of the great smoke stacks was their constant companion as they neared the summit of yet another toothed crag of rock.

The further they travelled, the more signs of death they saw. Bleached bones lay strewn all about in the rocks, but Uriel could not discern how they had come to be here. Not a scrap of meat remained on the bones, but it was impossible to tell whether they had been picked clean by scavengers or boiled free of flesh. Toxic clouds of smog and ash hugged the ground: noxious and polluted, lurking in cracks in the rock like predators with coiling tendrils of fog questing through the air like undersea fronds.

Uriel briefly removed his helmet to cough up a mouthful of brackish phlegm, its substance black and stringy. His enhanced metabolism enabled him to survive such pollutants in the air, but didn't make them any less unpleasant.

Several times they had been forced to traverse hissing rivers of molten metal as they flowed along great basalt culverts towards the smelteries and forges on the plains below. The heat of the mountains was growing and great geysers of scalding steam and hot ash spewed from vents and cracks in the rock. Were it not for their blessed power armour and bioengineered physiology, neither Uriel nor Pasanius could possibly have survived the journey.

Again, Uriel thought he caught sight of the reddish things Pasanius believed were following them, but each time they would vanish into the rocks and remain unseen. Flocks of the delirium spectres wheeled far overhead, but Uriel suspected that only the heat of the lava-hot rivers of metal and spouting plumes of boiling water kept them at bay.

As he passed near a zigzagging crack in the ground, a whooshing tower of boiling liquid suddenly erupted from it. Steam billowed around him, blinding him, and he stumbled away as a rain of objects began clattering around him, falling from somewhere above. Coughing and spluttering, feeling the heat scorch his oesophagus, he wiped moisture from his visor and watched a rain of bones fall upon the mountain, ejected from somewhere deep below the earth by the spouting geysers.

'Well, at least we know where the bones are coming from,' said Pasanius.

The strange objects Uriel had seen in the sky before they had discovered the scouring platform came into sight once more as they neared the summit, swollen leathery balloon-like objects with drooping cables that hovered in the sky over something beyond the ridge of black rock. Now that they were nearer, Uriel could see that his initial assumption that these were some form of crude barrage balloon looked to be accurate. Dozens of them floated ahead, their surfaces a patchwork of uneven fabric and, after what they had seen thus far on Medrengard, Uriel did not want to think too hard as to what they had been fashioned from.

The sound of the siege was not so distant now, the rumble of artillery drawing closer with every step they took.

'Whoever is attempting to take that fortress is determined indeed to keep up such a prodigious expenditure of ordnance,' said Uriel as he clambered up another sheer slab of rock. His gauntlets were battered and scarred, the razor-like rocks of Medrengard tearing at them with every handhold.

Pasanius nodded, his breath heaving as he climbed to join Uriel. The massive sergeant removed his helmet and spat the taste of the world from his mouth. 'Yes, I don't think we're the only ones interested in this Heart of Blood.'

'You think that's what the besieger is after?'

'I don't know, but it's certainly one explanation. Like you said, he's determined.'