Ventris turned and ran back into the arena, and with Pasanius's help, began freeing the pitiful remainder of their once-proud warrior band.

'If they don't kill you, follow my tracks!' called Vaanes. 'Sabatier said something about all the filth of Khalan-Ghol being flushed out into the mountains, so there's got to be a way out of here!'

Ventris nodded, too busy to answer, as the shrieks of approaching enemies drew nearer.

Cursing the Ultramarine for a fool, Vaanes set off into the depths of the cavern.

Uriel freed Leonid and Ellard, the coughing Guardsmen nodding their thanks as they clambered free and gathered up their own weapons. Soon they had freed the surviving members of the warrior band and set off into the macabre wilderness of the chamber, the great heartbeat and the screams of both victims and pursuers echoing weirdly from the rocky walls of the cavern.

Vaanes's trail was not hard to follow: the cloven bodies of mutants and overturned surgical tables clearly marking his passage through the cavern. The sounds of pursuit drew ever closer, their ragtag band weary to the point of collapse through a combination of sheer physical exhaustion and terror.

The sound of rushing fluids came from ahead and Uriel staggered into a vast, open sluice chamber filled with a multitude of filth-encrusted chutes and aqueducts that either pierced the walls of the cavern, rose up from below the ground or sluiced down from the upper tiers of the daemonculaba. The roaring noise of tonnes of excrement, waste matter and dead flesh rivalled the thudding of the Heart of Blood. Everything washed into a pool of stinking effluent that in turn poured through a colossal pipeway in the cavern wall.

A waterfall of filth, body parts, corpses and decomposing foetal matter poured from the cavern and away from the fortress. A way out…

Dead mutants littered the chamber, hacked in two by Vaanes's mad dash for freedom, and Uriel saw that there was only one way they would get out of this damnable place.

'We cannot fight them here! Into the tunnel!' he shouted and set off through the pool, wading thigh-deep in the bobbing detritus of surgical waste matter. He had no idea where the wide tunnel led or even if their situation would be improved by jumping in, but it had to be better than this.

The going was slow, but as he looked back over his shoulder to see a dozen or more of the Savage Morticians emerge into the sluice chamber, he pushed forward through the sludge with renewed vigour, sheathing his sword as he went.

The warrior band reached the churning, roaring waterfall of the tunnel and, one by one, leapt into its stinking darkness. Uriel heard the splash of thick, mechanical limbs entering the water behind him, and without a backwards glance, leapt in after his warriors.

Rushing filth enfolded him, its repulsive contents buffeting him as he tumbled downwards. Darkness and half-light warred with one another, and as he slipped beneath the surface of the scummy fluid, he was grateful for the shadows that hid the dead horrors flushed from the Halls of the Savage Morticians.

The roar of the tunnel was deafening, its slope too precipitous and the waters too deep to gain any handholds. He fought to the surface, gasping for breath and swallowing mouthfuls of foetid, frothing matter. The thunder of great pumps and the whining of enormous filters echoed from the encrusted walls and Uriel felt his skin burning with the pollutants and toxic discharge.

He slammed into the tunnel wall as it bent to one side, losing his grip on his bolter and watching as it spun off into the water. His fingers scrabbled for purchase, but he was being carried along too fast to find any kind of grip. Huge blades churned the water, hurling severed body parts and disembowelled carcasses into the air and Uriel desperately kicked out to avoid them. A rusted spar of sharpened metal slashed the water next to him and stinging water blinded him as he was carried along by the torrent, spinning him beneath the water.

As his head broke the surface, Uriel saw a huge foaming mass of spuming effluent ahead and heard the thunderous crash of water falling hundreds of metres. Jagged archipelagos of ruined flesh and foetal islands had agglomerated into decaying masses at the edge of a waterfall, and Uriel fought against the immense flow of the river of waste to direct his frenetic course towards one.

The roar of the waterfall and the stench of rotten flesh and organic waste matter filled his senses, threatening to overwhelm him. As the current hurled him onwards, he gave one last desperate kick and thrust his hands out to grip the mass of body parts before him. His hands closed on the clammy, greasy flesh, his fingers breaking the surface and spilling a mass of rotted innards into the water. Dead eyes and glassy features stared at him from the lifeless mounds as the sodden flesh disintegrated beneath his grip. He tumbled away, spinning around and cried out as he was swept over the edge of the waterfall.

Suddenly Uriel was in freefall, hurtling downwards through the air and tumbling end over end into the unknown depths. His limbs flailed uselessly as he fell and he roared in defiance at the darkness below. Was this how it was to end? Dying, broken to pieces within the refuse of the Iron Warriors?

He caught a glimmer of light on the fractured glass surface of water below and straightened his body to reduce the coming impact. His body knifed into the water, the filthy murk closing over him as he plunged into its inky black depths. Drowned corpses swirled in the cold darkness with him, rotted arms wrapping around him and eyeless skulls mocking him with their sightless gazes.

Uriel kicked for the surface, the breath hot in his supernumerary lung, fighting against the dead of the Savage Morticians who were dragging him down to lie with them forever.

His head broke the surface and he heaved a great breath of air, the dank stench of the rushing, water-filled tunnel welcome after the stinking depths. Swirling filth foamed around him and, as he shook his head clear, he heard and saw giant, churning blades chopping the water ahead of him, smashing the water and debris ahead to a fleshy morass.

Uriel fought against the current, spitting effluent from his mouth as he struggled against the worsening flow of water. The great fan blades spun too fast to dodge, but as he was carried ever closer, he saw that the leading edges of the fan did not quite reach the roof of the cavern…

Was it possible they didn't reach the bottom of the tunnel also?

Knowing he had only once chance of survival, Uriel took a deep breath and dived beneath the surface of the corpse-filled water, feeling the pressure waves of the huge blades buffet him from side to side as they foamed with water stained red with flesh and blood. The pounding pressure wave of the fan blades was a fierce force dragging him onwards, but with powerful strokes and kicks, Uriel swam downwards towards the bottom of the tunnel.

His lung burned with fire and his vision greyed, but through the murk of the water, he saw the soiled rockcrete base of the tunnel. Ahead, a thrashing mass of bubbles obscured the lethal edges of the fan blades, and he couldn't tell whether there was enough room for him to pass beneath. With no other choice before him, he pulled himself along the bottom of the tunnel, feeling the enormous beat of the blades.

He cried out, a breath of bubbles bursting from his mouth as he felt a searing slash across his back. Instinctively he pulled himself down and forward, letting what little air remained in his lungs pull him towards the surface as he cleared the blades. Uriel's struggles and kicks grew weaker and weaker, his limbs leaden as oxygen starvation took its toll on his already weakened physique.

And then his head broke the surface once more and he vomited up polluted matter, retching in a reeking lungful of air. The current beyond the fan blades was still strong, but he found that he could keep his head above the water with a little effort.