And the manufactorum sang. The conduits were the pipes of an organ. Whatever moved through them summoned notes of cancerous music. The deeper the Blood Angels ventured into the forge, the more complex the song became. The mouths of open conduits had teeth, and tongues lapped at their edges. They shaped themselves to the demands of the tune. The tongues vibrated. The octaves of the sick melody plunged so far beneath hearing, the vibrations would have shattered a mortal’s skeleton. They rose so high, Sanguinius tasted blood. The music was a polyphonic symphony of dark industry and darker intent. It was a hymn to ruin, and a threnody for hope. In the complex nodes that developed, he thought he heard the formation of a whisper. It was at the edge of perception, unwilling to declare itself yet. There were no syllables. It was the hesitation that came before a familiar word was pronounced.

Sanguinius was not alone in hearing the whisper. Raldoron spoke to him when First Company and the Sanguinary Guard broke through another horde of the corpulent, plague-bearing abominations. ‘Something is speaking here.’

‘And it wants us to listen,’ Sanguinius said. ‘Shut your ears to it. There will only be poison in the words.’

They were in a hall hundreds of yards wide, and they had a clear run for at least a mile. The space was lit by the conduits. They ran in thick clusters along the walls and the ceiling, two hundred feet up. Each was almost as wide as a Rhino, and they glowed, lit from within by the burning fusion of warp and matter they carried. They tracked their way down the curving tunnel like veins, their lines irregular, merging and branching but always feeding deeper.

‘The voices want us to advance,’ Raldoron said. ‘They are pulling.’

‘And we must advance for our reasons too,’ Sanguinius said. ‘There are matters where we have no choice. There are actions we are bound by destiny to take. That does not mean the consequences of the action are preordained.’ He needed this to be true. Please, Father, let it be so. ‘The foul song of this place may want us to go deeper. We will, and we will overwhelm the power within. It will rue its desire to lure us in.’

The tunnel curved sharply. Its immensity sighed. A great choir resounded, and the hall opened up into a chamber of even larger dimensions. Filling the centre was a nexus of conduits. They arrived from a score of corridors, from multiple levels. They tangled with each other, forming a gigantic knot.

‘A nerve cluster!’ Sanguinius shouted. It could be nothing else. The unwholesome light within flashed with maddening intensity, illuminating the chamber with a blinding stutter. ‘This monstrousness mimics life, and so makes itself vulnerable. Teach it pain!’