In the seeping black pools around its feet, spider-leg stalks and spastic pseudopods sprout and fade, jutting briefly from the steaming tar and dying back like a time-lapse pict-feed of nocturnal weeds. It is a shadow, straining to exist.

Voices chirp and snigger. Oll hears the voices of people he knows on the wind, and realises they are lies. He hears the voices of people he has not seen alive in thirty thousand years. Lies. Lies.

He hears John's laugh. He hears Pascal at Verdun, asking for a light. He hears Gaius on the Wall, cursing the rain and praising the virtues of Galician girls. He hears Commander Valis whisper the name of a forgotten god as they both flinch from the nuclear light blooming across the Panpacific horizon. He hears a man question the quality of bronze stirrups in strongly accented Scythian. He hears Zaid Raheem, pinned in his burning T-62, begging to die. He hears the shocktroopers around him moan as the officer tells them that their objective will be the Brumman Hives. He hears Iason and Orfeus, singing together. He hears Lieutenant Winslow dictating his will the night before Copenhagen. He hears Private Labella whistling as she fries beans and eggs the morning after the Socal Basin fell.

He hears his son, five days old, crying lustily in his crib, the day that the Norsemen landed. As if he knew, five days old and knew what was coming.

Oll raises his rifle, slips the toggle to full-auto, and fires.

The advancing darkness ripples as his streaming shots strike it. The darkness absorbs the bright bolts, but spatters too, each wound squirting fluid like milk.

The wounds vanish as fast as he makes them. The lactic blood fades. He cannot hurt it. It knows it, and he knows it. It does not just want him dead, it wants him broken. It wants his soul burned out with misery before it consumes him. It wants to anger him, wants him to feel rage and pain and frustration, and all the other human inadequacies of a thirty-five thousand year long life.

It knows he is a Perpetual.

Oll realises that suddenly, despite the pain robbing him of sense. He is caught up in the death of his son, a loss that took him three centuries to come to terms with, a loss he had pushed to the back of his over-stuffed mind, a loss M'kar has gone straight for, but even so, Oll realises.

It knows he is a Perpetual.

They would all be dead already, otherwise. It does not get to do this very often. It does not get to torment a being with such a great capacity for torment. Oll is a treat, a delicacy. All those heartless centuries of pain and loss and disappointment to tease out and relive, so many many more than a human life can encompass.

The pain is going to kill me, Oll thinks. The very thought of me is going to kill me. To remember all I have ever been through will kill me stone dead.

It will not be quick.

He stops shooting. His anger is as spent as his power cell. He throws his rifle aside. He turns his back on M'kar and walks away. He walks back to the others. They are still trying to sing, but it is not working.

'Keep going,' he urges, his voice breaking. 'Keep going... "forgive our foolish ways"... come on! Don't listen to it! Drown it out! Don't listen to its lies!'

He hears an old friend in a Dresden shop, chatting as he packs china in newspaper, 'in case the planes come tonight'. He hears his sisters calling his name from the cages on the caravan. He hears Him, the day they met, recognising a kindred being.

'The likes of us,' He says to Oll, 'the likes of us will leave our print on things down the ages. That is why we were made the way we were. The courses of our lives will not go unmarked.'

'Mine will,' Oll assures Him. 'I have no stomach for the games you want to play with the world. I just want an ordinary life.'

'My dear friend, you'll have as many of those as you want.'

It was summer, a meadow beyond the walls of Nineveh. He had never met another Perpetual before. He would never meet another like Him.

Look at him now. After all this time, having turned his back on all those games, and never being a part of any of them, look at foolish old Oll Persson. Crossing the universe on a knifeblade for his sake. Running a fool's errand through the warp and weft of the cosmos to stop his games from unravelling.

M'kar comes closer, gurgling laughter in the darkness. The voices swirl around him like blossom, the voices of Oll's life. The pain, the lies.

Oll and his pilgrims are in a circle, their backs facing outwards. Oll's back is directly to the darkness.

'Don't look,' he says. 'Don't listen. Sing up. Drown it out.'

They have stopped singing, though. They just look at each other. Bale Rane is to Oll's right, Katt to his left. Oll places a hand on each of their shoulders.

'Don't look,' he says. 'It's going to be okay.'

It is not, but what else is he supposed to say?

The voices are in his ears. The pain of his life is unimaginable. He knows the others are hearing their own voices too. Bale can hear Neve. Zybes is begging his mother to stop calling out. Krank is crying about someone called Pappi. Katt is just shuddering. Oll does not want to know what she is hearing.

He takes his hand off her shoulder slowly. If there is a chance at all, it is coming and it is going to be miniscule.

'M'kar!' she barks, an involuntary sound.

'Shhhh,' he soothes her through his tears.

'Mmmmkk!' she blurts.

'Easy,' he says. He lowers his hand to his waist, to his belt, to the wrapped athame. He can feel the daemon's breath on the nape of his neck.

The athame is warm too.

One chance. One tiny chance.

'Maloq!' Katt squeals, eyes rolling back.

'Hush now,' Oll says, taking hold of the dagger.

'Maloq! Maloq! Maloq!' she screams. Meaningless. He has lost her. She has gone.

'Maloq Kartho!' she cries, and vomits. 'Maloq Kartho! M'kartho! M'kar!'

He has the dagger. One chance.

He wheels around, blade raised.

[mark: ?]

The thing is gone.

Only ordinary darkness surrounds them. The smell of it has gone, and the heat of it. The tar has vanished.

Only the voices remain, just for a minute or so, receding into the distance like whisperers moving away into a room beyond.

Oll blinks. He realises his mouth is open to scream, so he closes it. He feels sweat on his flushed face. He lowers the blade.

'I don't' he starts to say.

He looks at the others. Bale is nursing the sobbing Krank. Zybes is sitting on the ground with his head in his hands. Graft has picked Katt up. She is limp.

'Oh God, no!'

She is not dead, though. There is vomit down the front of her clothes, and blood streaming from her nose.

'It went back,' she murmurs, looking up at Oll.

'Back?'

'Didn't you feel it? It was pulled back. It was yanked away from us, from here. It was needed somewhere else, for something more important than us.'

Oll shakes his head. He remembers John's words. Keep away from it for long enough. It will eventually have to give up and turn back.

'What in God's name?' Oll wonders, out loud.

'Maloq Kartho,' Katt says. Graft helps her to stand up. She is not steady.

'That's not a human name,' Oll says.

'No, it is,' she insists. 'I feel it is. A transhuman name, at least. Whoever Maloq Kartho is, Maloq Kartho is why M'kar had to go and leave us.'

'Then I pity poor Maloq Kartho,' says Oll.

Katt shakes her head. 'I don't know why, but I don't think you should.'

It has a destiny of its own.

[mark: ?]

Dawn breaks, soft over the thorn wood. The winds rise with it, rustling. Oll takes a bearing. He is pretty sure that the approach of M'kar was shielding them from the winds and prevented them getting a bearing.

The skies are clear, for now at least.

They have still got a long, long way to go, and it is not going to get easier.

'What do we do?' asks Zybes.

'Do we keep going?' adds Krank. 'Do we have a route? A... direction?'

'Boreas,' Oll tells them, putting the compass and chart away. 'The north-north-easterly. Boreas, or Mese, to the Grekans, at least. Nordostroni to the Franks. To the Romanii, Aquilo.'

He takes out the dagger and prepares to make the next cut. Their voyage will continue as it has been, like their lives and their destinies, unmarked.

That is why they might succeed.

'So what do we do?' asks Bale.

Oll puts his hand flat against the air and starts to cut.

'We push on,' he says. 'Okay?'

I am sorry. I used to have faith. I used to believe that there was more to the universe, that there was more than what we could touch and see, that there was a power higher than all of us guiding us, keeping us safe. I never told you because I knew you would be angry, because you might leave. Now you are gone anyway, and I do not believe it anymore. I am sorry. I was right there is another world beyond our dreams. I wish I could still believe it was a place of kindness. I do not want to go there.

N.

AFTERWORD.

If you'll forgive one final pun, Calth certainly left its mark upon me...

It was just over a year ago that Know No Fear landed in my editorial email inbox. I knew that Dan Abnett had been working on it for some time, but I wasn't expecting anything to be handed in before the Christmas break. Considering how much of a Horus Heresy geek I've become in the last seven years or so, I actually knew relatively little about the battle which comes to define the Ultramarines as a Legion in the Horus Heresy, and so I really had no idea what to expect from the novel.

I can honestly say and I think I Facebooked to this effect at the time that this was the first Black Library manuscript I'd ever read that made me want to laugh, cry, puke, and bang my fists on the desk in frustration all at the same time. It was compelling, gripping, painful, cathartic stuff. There are sections of that book that feel like a gut-punch, and others that make you want to start a whole new gaming army right then and there. Seeing Guilliman and his sons skipping merrily towards the precipice with looks of blissful ignorance plastered all over their patrician features it's like watching a documentary about a disaster, when you already know the ending. Far from being a straight-up military battle, this was bordering on sci-fi terrorism that quickly descends into warp-spawned madness.

One of my editorial comments to Dan at the time was something like: 'You've dropped in loads of plot hooks here aren't you going tell some more of these other stories?' Of course, his only response was, 'Maybe one day... But who says it has to be me that tells them...?'

In my mind, at least, that was when Mark of Calth was born. The uber-fan in me wanted to see the rest of Ventanus's legendary tale, and to find out just what the hell happened to the Campanile. I knew that there were still many hundreds of pages of plot left in the battles beneath the planet's surface, but the Horus Heresy always has a habit of moving on to the next big story and leaving a lot of the minor threads behind. This is where I think anthologies come in, since they provide a chance for short stories or novellas to pick up where the novels leave off, and vice versa. Speaking as an editor and following in the footsteps of The Primarchs, I'd like to see more anthologies themed towards specific characters or events as the Horus Heresy series continues.

The High Lords of Terra (that is to say, the authors) really took to this idea when we first tabled it for discussion. At the quarterly meetings at Games Workshop HQ, ideas began to take shape and sections of the Underworld War were marked out. Without even needing to add anything new into the mix, the existing continuity from Know No Fear and Graham McNeill's Warhammer 40,000 Ultramarines novels gave us some great starting points, and inspired a lot of the guys to get started straight away.

The interstitial snippets between the stories grew out of that initial rush of enthusiasm, too. There were so many story ideas flying around that we realised there wouldn't be enough pages to tell them all in full given Guilliman's predilection for note-taking and reviewing events in detail (why does that feel so familiar?) I invited everyone to write 100-word mini-stories to represent all these little disparate fragments of 'evidence' after the fact. With a little prefacing note from the primarch himself, these become less like colour text and more like an additional narrative in and of itself; some of them relate indirectly to the stories they append, and some of them hint at far darker things still to come in the wider Heresy series...

For me, the continuity is what makes all of these stories really special, regardless of word count. It's the crossover, the opportunity for little references to be made across different plotlines; for recurring themes like flooding, daemonic possession or the presence of simple ritual daggers which crop up time and time again. The Horus Heresy has always been an awesome exercise in collaborative writing, but this really is something else. Having up to ten authors simultaneously working on the same bit of background not only facilitates plenty of holographic storytelling, but also lets each of them write in their own individual style.

I say 'ten' because, of course, the Mark of Calth is still running.

At the same time as these fine gentlemen were penning the material for this anthology, other stories were being written to further explore the battles between the Ultramarines and the Word Bearers. Gav Thorpe has outdone himself with the exciting audio drama Honour to the Dead, which really depicts the 'epic scale' of Titan combat; similarly Nick Kyme continues the saga of Aeonid Thiel everyone's favourite bad boy in blue! in Censure. Also, Dan and cover artist Neil Roberts have begun work on the magnificent graphic novel Macragge's Honour, which follows the naval duel between the Ultramarines flagship and Kor Phaeron's battle-barge, fleeing for the Maelstrom at the end of Know No Fear. Any and all of these stories could have been included as prose in this anthology, but this way we get enough Calth action to satisfy even the most impatient Horus Heresy fan.

Besides, who knows how many more Calth-based stories are out there, waiting to be told?

Well, I know, obviously. But as always I can't say.

Laurie Goulding.

December 2012.

ABOUT THE AUTHORS.

Dan Abnett.