Several times my hearts quicken at the announcement of supposed enemy targets. I hunger for our foe. Perhaps we had found the shadow-corpse of Ungol Shax... or perhaps not. If his Bearers of the Word still haunt the passageways of the Penetralia, then they shall be mine. I have pledged my blade to their ending. This is a task unfinished. A mission without completion.

But time after time, our enemy targets turn out to be shadows and silhouettes, cast by our own light the very bedrock playing with us. The Cicatricians beg our pardon, but it is not difficult to see how the depths are rattling them. The scar tissue of their faces is taught with tension, their mouths unsmiling, their eyes peering through the slits of their helmets with dread expectation.

'Lord Pelion!' Evanz erupts. Such a warning had been sitting on the soldier's sun-scalded lips since entering the tunnel complex.

I turn, half-expecting another false alarm, but like the Cicatrician, I catch the shadow and its movement. Rocks don't move.

Before I can stop him, Evanz plucks off several las-bolts from his fusil. Light from the blasts ripples back down the passage, throwing more fleeting shadows along the rugged walls.

Something retreats.

Flushed with the validity of his sighting his fear moment-arily forgotten and a tension-fuelled rage taking over the soldier charges off after his shots with a roar.

'Hold!' I shout, but Evanz is already disappearing into the darkness. 'Hold your positions!' I bark back at the rest of the group before setting off after him.

It doesn't take me long to catch up, my armoured strides taking me with confidence back down the rough passage. I find him at an uneven crossroads one I don't recall passing through. Evanz's helmet is off. He's young, but his flesh is sun-scarred, lined with age and anxiety. He holds his empty fusil slackly at his side and his chest rises and falls beneath his plas-fibre breastplate. He stares with hollow eyes, but each of the passages offer nothing but fearful gloom.

He stiffens as I move him to one side. I scan the rocky convolutions of each tunnel, cycling through different optic spectra. Nothing.

'Back to the group,' I order. Evanz stands transfixed by the empty obscurity. 'Now!' I growl.

The soldier turns, deflated, and starts trudging back up towards his Cicatrix compatriots. I give the crossroads a last long, lingering look. 'I'm here,' I announce to the darkness, my voice carrying further than I expected. 'When you tire of your cowardice and playing games in the shadows, I am here.'

Back with the group, I exchange Evanz for one of the Tarxis Reservists on the rearguard and order Brother Phornax onwards.

It doesn't take us long to find Sergeant Grodin. Like a crystalline outcropping in the rock, we find the Cicatrician his back to the passage wall, his helmet turned up the tunnel and his fusil aimed back down it. I know little of the work of artists and remembrancers, but the sergeant strikes me as a sculptural study in panic and confusion.

We also discover the soldier he was searching for, a member of the Vospherous 55th, hiding in a small grotto. The trooper clutches his helmet to his breastplate and peers fearfully around a rocky corner, out into the tunnel. His scarred face remains aghast at the horror he must have beheld there, fixed in solidified shadow that smokes and steams under the glare of our lamps.

'Pelion,' Phornax calls.

The former Librarian had found Brother Daesenor. He could have been a statue from any compliant world, or one of the many depicting the noble and heroic exploits of the XIII Legion to be found across the worlds of Ultramar. For his lethal service on the fields of Komesh alone, Daesenor deserved as much. With his boltgun snug at his pauldron and his helmet optics lined up with the weapon's mean sight, the Ultramarine still looks ready to fire. I examine his gauntlet. His digit is fully depressed. The trigger has been pulled. Daesenor has been petrified in the moment that it might have saved him.

I feel a curse, common and uncouth, escape my lips. A tightness creeps into my voice.

'Phornax surely the Librarius has something to say on these unnatural matters?'

'Officially, the Librarius has nothing much to say about anything anymore, brother,' Phornax returns dispassionately.

'Unofficially, then?'

Phornax hesitates. 'The Heralds-that-were have clearly developed their sorcerous interests,' he tells me. 'They draw outlandish powers from the immaterial plane that enhance their already considerable capabilities.'

'Gifts like your own,' I ask.

'No, brother,' Phornax continues warily. 'Magicks and superstitious deviancies. Augmentations in the form of polluted artefacts and otherworldly bargains.'

'Could these perversities be responsible for these dark deeds?'

'Yes, brother.'

'And what weapons do we have to combat such deviancy?' I ask.

'You have my bolt and blade, as you have always done.'

I stare at him, and he stares back. Dodona looks on with some trepidation.

'I'll take point,' I tell him, pushing past. As our pauldrons scrape in the confines of the tunnel, I'm sure he can sense my frustration. He doesn't have to be witch-kin to do that.

Leading with my sword and shield, I move from corner to craggy corner, peering around with lamp and optics. As my light reaches down the tunnel lengths and through rocky corkscrew paths, I feel doubt infecting my thoughts. The desire to bring my enemy to battle can be heard in the grit-pulverising economy of my steps, in the fluid caution of rehearsed manoeuvres and positioning. The creak of my gauntlet about my weapons. Muscle and plate hydraulics primed to strike.

I want my enemy dead. Such need burns with perfect execution. No mistakes. The enemy will not benefit from my silent vexation.

At the same time I cannot indulge untruths. Finding Daesenor was unnerving: if a battle-brother of his skill had nothing to combat the dread powers of our Word Bearer foes, then there is little that my blade has to offer. I drew blood, fast and first, from the cheek of Deucalius of Prandium in a duel of honour. Draegal the Cardinal-Crimson lost helm and head to the seething sweep of my sword. The tentacular horrors of Twelve-Forty-Seven would have dragged me into their communal maw, had it not been for the snip and clip of my blade.

But if these monstrous bastards in the deeper darkness of the Penetralia took Daesenor in the instant before a bolt round could depart his barrel, then I fancy the flash of my blade might not be fast enough.

The junctions and intersections are the worst. At the dark nexus of adjoining passageways I feel the eyes of the foe upon me. The length of each holds the simultaneous, shadowy promises of an enemy acquired and latent doom.

I push on. There is little point in informing the others that we are now hopelessly lost. That is not the point. The enemy will find us. Of that, I am sure.

I hear a half nay, a quarter-stifled scream, and something clatters to the rocky floor. I spin around to find Evanz staring down one of the passages I just passed. His finger is outstretched in inexpressible horror. The fear is washed from his face and replaced by the ugly contortion of dread and disgust, and then the Cicatrician flashes from living being to crystalline shadow. First his trembling finger, then his arm and armour before his fear-sculpted face, the soldier suffers some kind of sorcerous petrifaction. Like a flesh-eating darkness, the shadow takes him, turning Evanz into crystallised tenebrosity.

The passage echoes with shouts of panic and horror. The remaining Cicatricians back into the immovable wall of armour that is Brother Phornax, as the former Librarian looks on with cold interest.

I cannot let our tormentors escape. Charging forward, I smash aside the glassy darkness that was Evanz. The muzzle-lamp from his dropped fusil still shines its beam up the tunnel... but there is nothing there.

I advance steadily. It will take more than 'nothing' to stop me.

My steps take me up the tunnel at speed, my sword and shield held close to my body. My suit lamps reach ahead of me, revealing the crooks and chicanery of the Penetralia passages. Whatever killed Evanz must be retreating just as quickly, since my light reveals nothing but a dead end, though it soon turns out to be a tight corner.

As I scrape my plate through the narrow gap, I find myself looking into the face of Olexander. The first of my party to go missing, he is in shadow also dissolving silently under the beams of my suit lamps. His statue soaks up the illumination like a sponge: the helmet, the crystalline shaft of a las-fusil clutched in one hand, the other hand stretched to hide his eyes from the sudden horror he spotted in the darkness of the tunnel entrance.

The tunnel entrance in which I'm standing.

Olexander stands at the head of crowd of such statues, and I realise that I'm back in the unholy temple-cavern, the twisting tunnels of the Penetralia somehow leading back upon themselves.

'Phornax!' I call out. 'The foe is playing a game that I cannot win. They've lost themselves and they wish for us to follow.'

Phornax enters the cavern through the narrowing with the same difficulty I experienced, yet Ione Dodona and the Cicatricians slip through with ease, not wishing to be left behind in the passageway on their own.

'The Word Bearers elude us,' I say, lending words to what everyone else is thinking.

'The Word Bearers are dead,' Phornax replies, his conclusion flat and lacking in the comfort such reasoning should inspire.

'Then who is it?' I demand. 'Those weakling cultists?'

Phornax sweeps his outstretched gauntlet across the statues, set in their ghoulish tableau. 'They invited something into the deep and the dark,' the former Librarian insists. 'Something they couldn't control. Something that destroyed them.'

I can't quite bring myself to believe it. So many men lost so swiftly. No shouts. No screams. No enemy sightings. Daesenor gone without a single bolt round discharged...

'Some... thing,' I echo.

'What is it?' Ione Dodona murmurs.

'Something that kills on sight,' Phornax replies. 'An unnatural. It hides in the shadows, waiting for us to seek it out with our lights. The horror of its otherworldly appearance alone seems enough to kill.'

The shadows lurch forward as the barrel-lamp belonging to one of the Cicatricians suddenly disappears. We all turn, weapons raised, but the unseen beast has left nothing but a figure, carved into the darkness. Dodona screams.

'Get back!' I roar. 'It's in here with us!' Bundling her behind me, I heft my shield high. She screams again. I cannot blame her. She is only human.

'Lord Emperor,' one of the soldiers cries. 'It's'

And the Cicatricians are gone, petrified into crystallised darkness. Their curiosity has killed them.

Without thinking, I almost turn to look before I catch myself. As quick as lightning, I grab Phornax and Dodona. 'Close your eyes, both of you!'

Fear is a stranger to my hearts. I am Legiones Astartes I am an Ultramarine but there is something primal about the fear of darkness. It is a fear of the unknown that even I can understand. I keep my eyes fixed upon the engravings at my feet.

'How can we kill it?' Dodona shrieks, gripping tightly onto my shield arm.

'We can't,' answers Phornax. Though he would deny it, I can feel him casting about with his feathery witch-sight, brushing against my soul in the darkness.

My concern for them becomes concern for all our people, all who eke out their existence beneath the standard of the 82nd Company in Arcology Magnesi. What if such an abomination were to find its way in?

I cannot allow that. Tauro Nicodemus must be warned.

'Brother Phornax,' I find myself saying, 'take Dodona and get back to the terminus chamber. Do not delay. Make your way back to Magnesi and inform the tetrarch of what we faced here. The Word Bearers doomed themselves and us along with them. He will know what to do.'

I feel objection building in my brother, but there's no time.

'Hurry,' I urge him.

Phornax slips a gauntlet under Ione Dodona's arm. Though she pulls hard on my vambrace, her dread allows her to be dragged away.

'What about you?' she shrieks back.

'Get Brother Phornax back to Magnesi,' I command her. I bring the blade of my sword up sharply and carve through the crystalline form of a Word Bearer statue nearby. It shatters, and the cacophony fills the temple-chamber the screech and fracture of tumbling obsidian echoes through the tunnels and crevices of the Penetralia.

'I'll draw it down to me,' I tell her, 'and give you a chance to escape.'

She starts to speak, but my blade smashes through two more Word Bearers.

'Go!'

The tunnel devours them like a great serpent. I stand alone in a sphere of my own meagre radiance. The blackness about me is overwhelming. I feel its intention to extinguish my very existence. Who will know of Pelion? Pelion the Lesser, who fought an ancient evil in the bowels of a doomed world like the heroes of ages past, freeing the empire of Ultramar from the tyranny of things-that-should-not-be?

I put my combat shield through a cultist. My sword cuts another in half. It rains shards of pure darkness, and the shattering feels too harsh for the chamber to contain.

Impossibly, amongst the raucous destruction, I hear a crash from the far end of the chamber. I spin around combat shield out in front of me and blade poised to strike. Some kind of unseen beast is headed straight towards me in the gloom.

It's been drawn. The distraction has succeeded. Now I will pay for my success.

I prepare myself for the horror I'm about to witness. Some dreadful thing, so disturbing in form as to be beyond my imagining. Some abominate existence that lives only to end my own. I feel the cold perversity of its solitude, its cursed power damning it to an eternity alone, ending even those foolish enough to summon it into the light. The violence of its advance burns with primordial fury. A tsunami of crystalline frag threatens to engulf me.

In that moment, I find myself thinking of Azul Gor. His face, full of bitterness and hatred, flashes momentarily before my downcast eyes. I think on his insistence that he could end me with a single world. Indeed, that word 'Penetralia' has led me to my doom.

Then, I realise.

Azul Gor survived the attentions of this beast of the beyond. Upon its summoning, the monster turned all who had gathered to witness it into solid darkness perhaps Azul Gor was not invited to the ritual. Perhaps he had other, more important duties, or perhaps he had merely sensed the coming destruction.

Regardless, escaping the Penetralia cost him his eyes.

The beast is all but upon me, vomited forth from the darkness and smashing an explosive path through the victim-statues. That it means to end me is clear.

I bring the sword to the side of my neck. There is only one thing left to do I run the blade across my throat. Its sharpened molecular edge slips into the groove created between my helm and plate seals. It slices through the power cabling and neural feeds. The light in my visor dies. The helmet's optics darken, and the data from my autosenses is cut.

I impose upon myself an artificial blindness. A disability that might save my life. Everything sizzles to static-shot black.

The impact of the beast knocks me clean off my feet, and I crash backwards through the shattered assembly. The thing feels like a charging beast of burden, some bull-grox on the stampede. It's hard to ascertain its size from such an attack, but the monster strikes me as a powerful quadruped, or a perpetually hunched thing lunging forwards on two more powerful legs.

No horns. No claws. No snaggle-toothed jaw.

Perhaps no jaws at all. Just an otherworldly bulk, full of fury and ancient hideousness.

The world has flipped about me in tumultuous darkness. I scramble back to my feet, sword and combat shield in hand. I shut down my suit lamps, plunging the entire chamber into an abyssal blackness. I doubt that this will faze the daemon-thing. I call upon my decades of training and my other superhuman senses. It is difficult as a Space Marine I rely on sight, augmented both genetically and technologically, to kill and to avoid being killed.

Instead I tune into the beast's movements. With my feeds and helm power cut, I cannot enhance my hearing. My ears are sensitive, though, even through the dead shell of my helmet. In a cave now carpeted with glassy shards of darkness, I can hear the crunch of its footfalls.

I immerse myself in a world of sound. I detect every creak of every shard; the whisper of pulverised blackness underfoot; crystalline fragments evaporating into wisps of powdered darkness.

It's circling me. It's confused. I haven't succumbed to its curse-power.

Perhaps I'm the first to do so. I enjoy its perturbation. I concentrate. I focus.

Crunching. The sound of more shards crushed into splinters. It's behind me now. It's behind me... A chill snakes up my spine, but I quash it with my resolve. Such misgiving belongs not in the minds of the Legiones Astartes.

The thing closes. I sense its horrid form at my back. I imagine its outline, and I strike.

I spin, crunching shadow-sand beneath my boots. I slam the monster with my combat shield, then back-slam it, my short blade sweeping forwards. The sword cuts through daemon-flesh, and cuts deeply.

I hear nothing. Not a screech. Not even a whimper of pain.

Perhaps the being doesn't even have a mouth, or any organ for such expression? Instead, I feel the ache of its agony within my mind.

I turn on my heel, my blade biting into it once more from the flank. I hear the crunch of an agonised stumble. The bastard thing certainly didn't like that.

It circles, but gives me a wide berth. I turn with it, my sword and shield raised.