Uriel watched in horror and amazement as the crushed and mangled metal of Pasanius's arm ran like liquid mercury and the destruction Obax Zakayo had done to it vanished utterly, every single dent, scrape and imperfection renewed until the arm was as unblemished as the day it had first been grafted to the sergeant's stump of an elbow.

'Pasanius…' breathed Uriel. 'What… how?'

His friend rolled onto his side, hiding his newly healed silver arm from Uriel's sight.

'I'm so sorry…' he wept. 'I should have…'

Honsou loomed over Pasanius, pulling the sergeant's silver arm away from his chest where he cradled it. He slid his own augmetic fingers across the silver perfection of Pasanius's mechanised arm and looked at his own glossy, mechanical limb in leering anticipation.

'Take them to the Halls of the Savage Morticians and give them to the Savage Morticians, but tell them to keep this one alive… I want this arm.'

Honsou rose and walked over to Uriel, his features twisted in betrayed anger. 'But give Ventris to the daemonculaba, he's not worth anything else. Let them abuse his body and take what they want from him before shitting him out.'

The journey to the Halls of the Savage Morticians was as fraught with insane visions and delirious apparitions as the one towards its inner sanctum. The interior of the tower flaunted the laws of nature and physics with nauseating perspectives and impossible angles that fought the evidence of Uriel's senses.

They descended winding spiral stairs that looped around others in a dizzying double helix pattern, with shuffling slaves, gold-robed acolytes and Iron Warriors climbing or descending - Uriel wasn't sure which - above them in defiance of gravity.

Obax Zakayo, Onyx and the forty Iron Warriors had marched the warrior band from Honsou's chambers, back through the chasm-split chamber and Titans towards the dirge-echoing cloisters of the tower. Beyond that, Uriel could not say what route their captors led them, the chaotic architecture of the tower defeating his every attempt to remember their route of travel.

Battered, without weapons and heads bowed in defeat, the Space Marines and Guardsmen were herded through darkened, dusty corridors - though Pasanius kept his distance from Uriel and would not meet his eyes. Such passivity chafed on Uriel's sense of honour, but to attack their captors now would see them all slaughtered. And while he still had a death oath to fulfil and continued to draw breath, he knew there would be time enough to fight.

Their march led ever onwards to what Honsou had called the Halls of the Savage Morticians, where dwelt the Savage Morticians. Uriel had caught more than a little fear at the mention of these individuals, and did not relish discovering the reason for that fear. Was the creature that had tried to take them from Onyx as they had entered the tower one of these beings? Uriel had a horrible suspicion they would find out all too soon.

Their march came to an abrupt end when Obax Zakayo hesitantly approached a low, red-lit archway, its edges delineated with hooks, long needles and gory meat racks hung with cuts of dressed human flesh. Plaintive cries and the hiss of sizzling meat gusted from within, carried upon the stench of blood and despair. Something moved within the glowing arch, a shambling, misshapen thing.

Obax Zakayo hesitated before passing beneath the archway, the click, click of metal claws on stone and the echoes of a booming heartbeat echoing from the dripping archway ahead. The Iron Warriors' apprehension was plain to see. Onyx displayed no such hesitancy, passing the threshold into the domain of the Savage Morticians without fear.

Uriel felt foetid warmth as he passed through the arch, glancing around to see what could so discomfit the Iron Warriors. The silver fire of Onyx's eyes and veins cast a faint glow around the chamber, and Uriel was suddenly grateful for the dimness of the light as he saw macabre hints of all manner of grotesque experimentation hung from the walls and displayed within jars of milky fluid. The chamber's occupant limped towards Obax Zakayo, its every step obviously painful.

Uriel saw its naked body was a melange of limbs and appendages from Emperor alone knew how many other bodies. Its head was stitched on backwards, with rusted copper augmetics replacing its eyes and ears. It bore itself up on legs that had obviously belonged to two people of greatly differing size and its torso was a spiderweb of poorly healed surgical scars. Perhaps it had once had a gender, but nothing remained of its groin to tell. The thing's arms dangled before its chest in an asymmetrical loop, its hands grafted together in one lumpen mass of fused flesh and bone.

'What want you?' it slurred from a mouth thick with ropes of drool. 'Not welcome.'

'Sabatier,' said Onyx. 'We bring offerings for your masters. New flesh.'

The creature named Sabatier transferred its gaze from Onyx to the warrior band and dragged itself painfully towards Ardaric Vaanes. It reached up to rub its fused fists against his face, but Vaanes pulled away from its bruised flesh before it could touch him.

'Don't touch me, you monster,' he snarled.

Sabatier chuckled - or gargled, it was hard to be sure - and turned back to Onyx.

'Defiant,' it said as Vaanes lunged forwards and grabbed its neck, twisting its head around with a loud crack of bone. It sighed once and dropped to the ground. Obax Zakayo stepped in and gripped Vaanes's armour with his mechanised claws, lifting him from the ground with a roar of anger.

'And strong…' said Sabatier from the ground as it awkwardly picked itself up. Its head lolled on its shoulders, a sharp-edged shard of bone jutting from its patchwork skin.

It waved the fleshy loop of its arms at Obax Zakayo. 'Leave him be, masters always prefer flesh be strong, than weak, starved things normally get. Maybe defiant one get lucky and masters make him like me. Dead, but not cold in ground.'

'He should be so lucky,' said Obax Zakayo, dropping Vaanes back to the ground.

'No, will not be,' said Sabatier, raising its head and speaking a guttural incantation.

At the sound of its phlegm-filled voice, the far wall of the archway shimmered and vanished, the noise of screams and the pounding heartbeat filling the chamber. A great, iron-meshed cage lay beyond, and the Iron Warriors pushed them into its centre with brutal clubbings from their bolters.

Once they and their captors had entered the cage, Sabatier looped its arms around a yellow and black chevroned bar and, with some difficulty, pulled it shut across the cage's door. As the door clanged shut, the cage lurched and a grinding squeal built from above as ancient mechanisms engaged and the cage began to descend into the depths of the tower.

Uriel looked down through the grilled floor of the cage, seeing only a dimly glowing shaft constructed of oily sheets of beaten iron. The bottom was lost to perspective, and Uriel saw that there was no way that this shaft could be physically contained within the tower. The fact of the shaft's spatial impossibility did not surprise him any more.

Vaanes sidled close to Uriel as the shaft continued its descent, gaining speed as it went until the metal sides were screaming past.

'We have to get out of here soon. I don't like the sound of these Savage Morticians.'

'Nor I,' agreed Uriel. 'Anything that worries an Iron Warrior cannot be good.'

'Perhaps your sergeant with that self-repairing arm can fight his way clear. Where in the hell did he get that?'

'I wish I knew…' said Uriel as the speeding cage finally slowed before coming to a juddering halt. Sabatier hauled open the doors on the opposite side of the cage.

The Iron Warriors beat them from the cage into a gradually widening tunnel hacked through the rock. At its end was a pulsing red glow, a chorus of screams, hissing, clanging and thumping engines. But drowning everything beneath its thudding, regular hammering was the pounding of a deafening heartbeat.