‘There is no forgiveness. Better to die twice than betray the Emperor. You made the wrong choice.’ And Justinian’s assault bolters would bark, or his fists would swing, leaving red ruin where men had knelt.

Battle was replaced by a fragile calm for a time. The building evinced little of the touch of Chaos, being fairly made of plasteel plating upon a ferrocrete core of near indestructible thickness. The sheer mass of it dulled the thunder of battle outside upon the plains, so that the worst of it was felt only as gentle tremors, and the rest they did not notice at all. Machines hummed in the fabric of the building. Although the decoration was barbarous – the grisly trophies nailed to walls and set upon spikes told of the Iron Warrior’s bloodier proclivities – the warp was absent.

When they reached fire control, that changed. A large room of three stepped tiers, the tower’s fire-control centre was similar in design to those in Imperial fortifications. The two had the same origin, so that was to be expected, but what occupied the fire-control centre here would never be found in any Imperial facility.

Where ranks of tech-thralls and servitors should sit guiding the weapons of the fortress to the commands of their masters, there was instead a thick organic mess. Tendrils of noisome matter linked wall to wall. This filthy mass grew thicker in the middle, somehow coming together to make a living thing, though at its edges it was nothing more than a set of flimsy, folded membranes. At its thickest part, pulsing veins made the whole thing quiver. A soft keening sounded from somewhere, and an intolerable sense of suffering pressed at the Primaris Space Marines’ minds.

‘Emperor preserve us,’ said Justinian.

Exposure to warp-born horror did nothing to lessen his revulsion. Countless times he had seen creatures made of the pressed flesh of men, mutant weavings of corrupted genes, and daemons trapped in machine and mortal form. No matter how often he saw these things, they never failed to disgust him.

‘If any pure machine exists here, then I commend your spirits to the god of Mars,’ he said loudly. He meant it sincerely. Though he had no belief in the Emperor-as-Omnissiah, he respected the machines’ own beliefs.

He raised his gun and opened fire. Aldred joined him, raising both guns and filling the rotten mess with explosive rounds. The keening became a scream. Gunfire blew huge holes in the organism, opening its innards to the smoking air. Hot yellow liquid slopped from it in amounts the thing could not possibly contain. The scream grew so loud it made the noise-suppression equipment of their helmets thrum. When it abruptly cut out, their aural equipment squealed with relief. The oppressive nature of the room disappeared along with the creature’s death cry.

‘Whatever that was, it is dead,’ said Aldred. Fyceline smoke wisped from his guns. Heat bloom discoloured their muzzles.