But precognition was never perfect. The second shell grazed the other Space Marine’s armour, knocking him off-balance but failing to drop him. The warrior regained his poise almost instantly, falling low and twisting round. A brace of white-hot plasma bolts flew directly at Arvida.

By then the Corvidae had already moved, darting back into the protection of the statue as the energy-pulses hammered into the stone. It broke open on the second impact, cracking from head to foot and toppling into pieces. Arvida burst left from the tumbling remnants, squeezing off another controlled salvo from his bolter.

His enemy hadn’t stood waiting to be hit, but had closed in for the kill. He had a chainaxe in his left hand, buzzing like a furious swarm of insects. His movements were powerful and fast, aimed perfectly and backed up with crushing force. The chainaxe whirred in close, going for the chest then suddenly banking up towards Arvida’s neck.

Without precognition, he’d have been dead. His adversary was stronger, quicker and had the momentum behind him. But when the blades whistled into position, Arvida had already moved, weaving away from the preordained pattern of the cutting edges. Shifting his weight expertly in the wake of the axehead, he pivoted out of contact and fired three rounds into his enemy’s face at point-blank range. They detonated immediately, throwing both of them apart with the crack of the explosion.

Arvida checked his fall, springing back up, and prepared to fire again. He didn’t need to. His enemy’s face was ruined, a hollow shell of blood, armour-chips and skull-fragments.

For a moment, Arvida stood over the defeated warriors, feeling his pulse throb in his veins. It was the first time he’d got close to those who’d hunted his squad through the ruins.

As he looked at the livery on the shoulder-guards, his satisfaction at the kill was replaced by shock.

Then there were more sounds of pursuit, echoing in his future-sense like the memory of a dream. Other warriors were closing fast.

Arvida broke into a run, heading into cover past overhanging building-remnants and loping quickly towards the lander coordinates. There was no way he could fight to Kalliston’s position alone, and he’d help no one by getting pointlessly killed. The only option was to gain the ship, take off and attempt an airlift recovery.

It was as he went, darting between shadows like a ghoul, that he tried to make sense of his attackers’ identity.

But it made no sense. No sense whatsoever.

MY QUESTIONER’S ARMOUR, which I had thought was grey in the near-total dark, is a dirty white. The shoulder-guards were once a bright blue, though every exposed surface on his battle-plate is covered by a translucent layer of brown-red filth.

So he is a War Hound. Or, as I believe they’ve started calling themselves, a World Eater. The assumed name is ludicrous, a perversion of everything the Legiones Astartes used to stand for. However, to the extent that I understand the ways of other Legions, it is perfectly accurate. They do devour planets. I have heard tales of outrages under Angron’s insane tutelage that make my stomach turn. The only Legion with a comparable reputation is the Wolves, so perhaps it’s not surprising that I found it so easy to believe I was held by one of Russ’s dogs.

In the dark, I had imagined my interrogator being something akin to a beast, slavering on the edge of madness. The reality is only a little less disconcerting. The World Eater’s head is uncovered, exposing the full distortion of his features. His flesh is bronzed and supple, though there are deep wells of shadow under his low brow. He has long cheekbones and a blunt, slabbed chin. His head is shaved bare, the scalp puckered with scars. There are regular marks on his temples and a series of iron studs further up on the smooth skin. In another Legion, those studs might have indicated long service, but I know their purpose on him. As with all his kind, there are implants under the flesh, implants long forbidden by the Emperor. The prohibition is for good reason. They accelerate the rage and stoke it, amplifying an already testosterone-charged kill-factory into a bringer of truly ludicrous levels of violence.

And there is something else. The Space Marine before me is no ordinary World Eater, if such a thing could even be said to exist. A few select members of that terror Legion have carved a name for themselves outside their closed, brooding brotherhood. This is one of them. I know, without needing to use my fractured mind-sight, that I am in the presence of Khârn, Captain of the Eighth Assault Company and equerry to the primarch. If I needed any confirmation that my death is close, I have it now.

He stares at me. His eyes are the yellow of curdled milk, rimmed with red where the lids are pulled back. Veins pulse at his temples, bulging darkly against taut skin. He has a line of drool still, glistening against his chin. If I ever wish to conjure up the image of a psychopath again, I will have this picture to bring to mind. Khârn is almost a parody of himself, the apotheosis of martial insanity, a walking furnace of unfettered bloodlust.

He was not always like this. Even in the stories I have heard, he was ferocious but not mad. Something has happened to change him. Something terrible.

‘Why have you brought me here?’ I ask.

Khârn smiles, but there is no mirth there. It is as if his facial muscles pull naturally into a leer unless continually suppressed.

‘I am here for the same reason as you,’ he says. ‘Hunting through the wreckage, looking for something to salvage.’

Even in my weakened state, that image brings a choking, bitter laugh to my lips. I cannot imagine World Eaters salvaging anything. They are the soul of destruction and nothing else.

‘And did you find what you were looking for?’

Khârn nods.

‘There is a cavern, far below the surface of Tizca. You will know of it – the Reflecting Cave. We speculated that the Wolves might have missed it, despite their reputation for thoroughness. There was something down there I was ordered to retrieve.’

He withdraws an iron pendant from his armour. It is fashioned into the shape of a wolf’s head howling against a crescent moon. The metal is black, as if placed in a fire for too long.

‘The Moon Wolf,’ says Khârn. ‘Your primarch used it to make contact with Horus. It was a part of the Warmaster’s armour once, and so has a sympathetic connection with him.’

He speaks as if those words should mean something to me, though I struggle to see the significance of them.

‘It could be used again, and Horus has no wish to be reached for further discussions. It will be destroyed, and another potential chink in our defences will be closed off. Then, thank the gods, I shall be free to undertake more fulfilling work for the cause.’

‘I do not understand,’ I say, and the passing reference to godsmakes me uneasy. ‘What has Horus to do with this? What has happened here?’

Khârn doesn’t smile this time, but I can sense a vicious amusement cradling in him. I sense more than that, too. He is burning with agony, an agony that can only be discharged by murder. The Moon Wolf was not the only reason he came to Prospero.

‘You really know nothing,’ he says. ‘I had planned to torture you for your secrets, but I see that you have none. So I shall torture you another way.’

He leans forwards, and I recoil at the raw-meat stench of his breath.

‘Listen to me, Thousand Son, and I will tell you a story. I will tell you of the great movement that is taking place across the galaxy. I will tell you of the ruin of all your primarch’s hopes and the final triumph of the virtuous strong over the craven weak. And then, before I kill you, I will tell you of the final destination of this crusade, the crusade men are already beginning, in their infinite ignorance, to call the Heresy.’