'I think we know what happened to the Jaegers,' he said grimly. 'And probably most of the labourers besides.'

'Most of them?' Astelan said.

'A worm didn't send the radio transmission to Aldurukh,' Zahariel said.

'Emperor protect us,' the chapter master hissed in disgust.

'It's been done before,' Attias said. 'The Knights of Lupus turned their beasts on us, remember?'

'But the Knights of Lupus are no more,' Astelan said sharply. 'And the great beasts driven to extinction. So where did these vile things come from?'

'That's not important right now,' Zahariel said, eager to change the subject. 'If the worms carried off the bodies of the Jaegers, it means they've got a nest and an egg-laying queen down here.'

Astelan nodded in agreement. 'The queens are much larger than the drones,' he warned.

'Then she must be up ahead, near the thermal core,' Zahariel declared. He checked the load in his bolt pistol, then holstered it and pulled a frag grenade from his belt. 'Grenades first, then we charge. I'll take the lead. Any questions?'

There were none, of course. The warriors of the squad had their orders. The Astartes returned to their formation and readied their weapons without hesitation. Zahariel took Astelan's place at the head of the group and set off down the corridor at a swift pace. As he did, he summoned his power once more and sent it questing down the passageway ahead. He sensed more worms waiting in ambush at the far end of the corridor and lashed the monsters with a wave of psychic energy. A hideous screeching filled the air, and powerful, armoured bodies burst from the concealing roots, thrashing in their death agonies. Zahariel struck them again, channelling every ounce of his rage into the blast, and the worms became shrieking pyres of purple and indigo flame.

Zahariel primed the grenade in his hand. 'For the Emperor!' he cried, and hurled it down the corridor. Nine more grenades followed an instant later, flashing past his head in flat, precise arcs to detonate just beyond the entrance to the core chamber. More shrieking rent the air as shrapnel scythed through the creatures hiding around the entranceway. Zahariel answered them with a furious shout of his own and broke into a run, his force staff blazing like a firebrand.

A swarm of reaver worms awaited their charge, ready to defend their nest. The Librarian hurled a torrent of psychic flame into their midst, immolating a score of the creatures and stunning the rest. He and his brothers crashed a moment later, and the battle was joined in earnest.

Zahariel swept his force staff in a crackling arc and killed two worms lunging at him from the right. Another monster struck from the left, fixing its mandibles about his ceramite pauldron; in one swift motion he drew his bolt pistol and decapitated the creature with a single, well-aimed shot. Around him, chainswords howled and bolt pistols hammered as the Angels of Death slaughtered their foes.

The chamber was a huge, man-made cavern that, rose to a curved, dome-like ceiling thirty metres above their heads. The huge cylinder of the thermal core itself dominated the centre of the chamber, rising from a bore that had been drilled more than five hundred metres into the bedrock of the planet and disappearing through an opening at the apex of the dome, where it carried geothermal heat to power exchange units that supplied the rest of the plant.

The air inside the cavernous space was gelid with heat and the stench of rot. The air around the thermal core shimmered like a mirage, and a powerful sense of dislocation threatened to overwhelm Zahariel. The cables of his psychic hood burned into his skull, and a spike of dull agony bore into his brain despite the effects of the dampener. The barrier between the warp and the physical world had been weakened here, and the sense of madness and corruption was almost palpable, like a layer of oil coating his skin. Sorceries had been worked here, his training told him, and the heart of it lay only a few dozen metres away.

At the centre of the chamber, right at the feet of the columnar thermal core, lay a massive pile of corpses. The top layer, Zahariel could see, wore bloodstained uniforms of forest green - the Jaeger relief force that had been drawn to the site. But there were hundreds more, the Librarian estimated - likely the entire labour force of the plant as well.

Hissing and screeching, the defenders of the reaver worm nest assaulted the Dark Angels from all sides. Zahariel blew one out of the air with a pair of shots from his bolt pistol and blasted two more into burning husks with a sweep of his staff. The Astartes kept their octagonal formation, facing outwards and slashing away with their chainswords at any monster that came within reach. The training of the Legion - and the rites of the Order before it - served the warriors of Caliban in good stead, and the bodies of their foes began to pile about their feet. But every time they slew one of the monsters, Zahariel felt the invisible energies swirling in the room grow more turbulent. Whatever dark designs had been set into motion here, their actions only served to energise it further.

'Press forward, brothers!' Zahariel cried, and the squad responded instantly, shifting their formation towards the thermal core one measured step at a time. The surviving worms redoubled their attack, leaping for perceived openings in the warriors' formation, but each attempt was met with a scything blade or the muzzle flash of a bolt pistol. The Dark Angels advanced relentlessly across the chamber, leaving a trail of broken, bleeding monsters in their wake. With each step, however, the air seemed to grow more and more charged. Strange coruscations crackled along the length of the core, and unearthly groans reverberated around the Astartes. As they drew nearer to the pile of corpses, Zahariel could see that they had been laid inside a vast spiral. The curving line was formed of a procession of carefully-shaped runes, each one carved into the floor by a plasma torch and filled with congealed blood. The symbols smote his eyes and sent jagged needles into his brain when he tried to focus on them, and the effect grew worse the farther along the spiral he stared.

The surviving worms had abandoned their frenzied attack, and were retreating away from the Astartes in a ragged circle, their swift, sinuous forms slithering across the damp ground as they lurked beyond chainsword range. The members of Zahariel's squad continued their bloody work, picking off the monsters with careful shots from their bolt pistols. The death energies added to the growing maelstrom, stoking the invisible fires further. Zahariel gritted his teeth at the mounting pain in the back of his skull and drove his squad forward a stubborn step at a time. They were ten metres from the corpse pile now; he could see that each body had been daubed with runes of its own and coated in a translucent slime that shimmered faintly in the strange energies flickering overhead. As the ball lightning flashed, Zahariel glimpsed a sigil of some kind that had been painted against the side of the thermal core, about a dozen metres above the mound of bodies. But before he could focus on what it was, the worms suddenly turned about and rushed at his squad.

A terrible sense of foreboding gripped Zahariel. Before he could shout a warning, however, nine bolt pistols hammered, and every remaining worm was blown apart in a single, simultaneous volley. Their death energies smote the ether like a hammer blow, and the pent-up forces in the chamber erupted.

Zahariel felt the sense of dislocation sharpen dramatically as the barrier between the realms began to unravel. He staggered as his psychic dampener threatened to overload, sending shooting spikes of agony into his brain.

Before him, the pile of corpses began to stir.