'Second Company!' shouted Torgaddon. 'Stand to, weapons free!'

'Where's it coming from?' bellowed Horus.

'Can't say,' replied Torgaddon. 'The mist's playing merry hell with the acoustics.'

'Find out,' ordered the Warmaster.

Torgaddon nodded, demanding contact reports from all companies. Garbled shouts of impossible things came over the link, along with the louder bark of heavy bolter fire.

Gunfire sounded to his left and he spun to face it, his bolter raised before him. He could see nothing but the staccato flashes of weapon fire and the occasional blue streak of a plasma shot. Even the external senses of his armour were unable to penetrate the creeping mist.

'Sir, I think we—'

Without warning the swamp exploded as something vast and bloated erupted from the water before him. Its gangrenous, rotten flesh barrelled into him, its bulk sufficient to knock him onto his back and into the swamp.

Before he went under the dark water, Torgaddon had the fleeting impression of a yawning mouth filled with hundreds of fangs and a glaucous, cyclopean eye beneath a horn of yellowed bone.

'I don't know. The command net just went crazy,' said Moderati Primus Aruken in response to Princeps Turner's question. The external surveyors had suddenly and shockingly filled with returns that hadn't been there a second ago and his princeps had demanded to know what was going on.

'Well find out, damn you!' ordered Tumet. 'The Warmaster's out there.'

'Main guns spooled up and ready to fire,' reported Moderati Primus Titus Cassar.

'We need a damn target first, I'm not about to fire into that mess without knowing what I'm shooting at,' said Turnet. 'If it was Army I'd risk it, but not Astartes.'

The bridge of the Dies Irae was bathed in a red light, its three command officers seated upon their control seats on a raised dais before the green glow of the tactical plot. Wired into the very essence of the Titan, they could feel its every motion as though it were their own.

Despite the mighty war machine beneath him, Jonah Aruken suddenly felt powerless as this unknown enemy arose to engulf the Sons of Horus. Expecting armoured opposition and an enemy they could see, they had been little more than a focus for the Imperial forces to rally around so far. For all the Titan's overwhelming superiority in firepower, there was little they could do to aid their fellows.

'Getting something,' reported Cassar. 'Incoming signal.'

'What is it? I need better information than that, damn you,' shouted Turnet.

'Aerial contact. Signal's firming up. Fast moving and heading towards us.'

'Is it a Stormbird?'

'No, sir. All Stormbirds are accounted for in the deployment zone and I'm not picking up any military transponder signals.'

Turnet nodded. 'Then it's hostile. Do you have a solution, Aruken?'

'Running it now, princeps.'

'Range six hundred metres and closing,' said Cassar. 'God-Emperor protect us, it's coming right for us.'

'Aruken! That's too damn close, shoot it down.'

'Working on it, sir.'

'Work faster!'

The dense mists made looking through the frontal windshield pointless; nevertheless, there was an irresistible fascination in looking out at an alien world - not that there was much, or indeed anything, to see. Thus, Petronella's first impressions upon breaching the upper atmosphere were of disappointment, having expected exotic vistas of unimaginable alien strangeness.

Instead, they had been buffeted by violent storm winds and could see nothing but the yellow skies and banks of fog that seemed to be gathered around another unremarkable patch of brown swampland ahead.

Though the Warmaster had politely, but firmly, declined her request to travel to the surface with the warriors of the speartip, she had been sure there was a glint of mischief in his eye. Taking that for a sign of tacit approval, she had immediately gathered Maggard and her flight crew in the shuttle bay in preparation for descent to the moon below. Her gold-skinned landing skiff launched in the wake of the Army dropships, losing itself in the mass of assault craft heading to the moon's surface. Unable to keep pace with the invasion force, they had been forced to follow the emission trails and now found themselves circling deep in a soup of impenetrable fog that rendered the ground below virtually invisible.

'Getting some returns from up ahead, my lady,' said the first officer. 'I think it's the speartip.'

'At last,' she said. 'Get as close as you can then set us down. I want to get out of this mist so I can see something worth writing about.

'Yes, ma'am.'

Petronella settled back into her seat as the skiff angled its course towards the source of the surveyor return, irritably altering the position of her restraint harness to try to avoid creasing the folds of her dress. She gave up, deciding that the dress was beyond saving, and returned her gaze to the windshield as the pilot gave a sudden yell of terror.

Hot fear seethed in her veins as the mist before them cleared and she saw a huge mechanical giant before them, its proportions massive and armoured. Saw-toothed bastions and towers filled her vision, massive cannons and a terrible, snarling face of dark iron.

'Throne!' cried the pilot, hauling on the controls in a desperate evasive manoeuvre as roaring fire and light horrifyingly filled the windshield.

Petronella's world exploded in pain and broken glass as the guns of the Dies Irae opened fire and blasted her skiff from the yellow skies.

Loken surged backwards in horror and disgust as the cadaver attempted to strangle the life from him with its slimy fingers. For something as apparently fragile as a rotted corpse, the thing was possessed of a fearsome strength and he was dragged to his knees by the weight and power of the creature.

With a thought, he flooded his metabolism with battle stimms and fresh strength surged into his limbs. He gripped the arms of his attacker and pulled them from its reeking torso in a flood of dead fluids and a wash of brackish blood. The fire died in the thing's eyes and it flopped lifeless to the swamp.

He pushed himself to his feet and took stock of the situation, his Astartes training suppressing any notion of panic or disorientation. From all around them, the bodies he had previously thought to be lifeless were rising from the dark waters and launching themselves at his warriors.

Bolters blasted chunks of mouldered flesh from their bodies or tore limbs from putrefied torsos, but still they kept coming, tearing at the Astartes with diseased, yellowed claws. More of the things were rising all around them and Loken shot three down with as many shots, shattering skulls and exploding chests with mass-reactive shells.

'Sons of Horus, on me!' he yelled. 'Form on me.'

The warriors of 10th Company calmly began falling back to their captain, firing as they went at the necrotic horrors rising from the swamp like creatures from their worst nightmares. Hundreds of dead dungs surrounded them, mouldering corpses and bloated, muttering abominations, each with a single milky, distended eye and a scabrous horn sprouting from its forehead.

What were they? Monstrous xeno creatures with the power to reanimate dead flesh or something far worse? Thick, buzzing clouds of flies flew round them, and Loken saw an Astartes go down, the feeds on his helmet thick with fat bodied insects. The warrior frenziedly tore his helmet off and Loken was horrified to see his flesh rotting away with an unnatural rapidity, his skin greying and peeling away to reveal the liquefying tissue beneath.

The bark of bolter fire focussed him and he returned his attention to the battle before him, emptying magazine after magazine into the shambling mass of repulsive creatures before him.