The long iron hall was filled with shadows.

In the echoing space, nothing human moved. No one had the courage to enter, for fear of what lay beyond. No one dared to set foot inside, to take a breath of the air within and challenge fortune.

At least, no man dared.

Concealed in the gloom, a heavy hatchway opened with a hissing chorus of pressure-locks and two hulking figures entered the chamber. These were not men. They towered over common humans, these scions of battle. Once, both of them had been proud to stand amongst the Emperor’s Legiones Astartes. Brothers in conflict, comrades against adversity. Now fate had set them upon separate paths.

One was clad in wargear the colour of storms, adorned with a golden eagle cuirass, his helm mag-locked at his waist and his sword at his back. Nathaniel Garro, Knight Errant and Agentia Primus of the Regent of Terra. The other, a former warrior stripped of his armour, weapons and the desire for war. Meric Voyen in his robes, once an Apothecary of the Death Guard Legion and now a soul in search of peace.

‘Captain! Please, no! Wait!’ cried Voyen, trying in vain to halt Garro’s furious strides.

‘I will not,’ came the reply.

‘Stop! I beg of you, let me explain!’

Garro shook his head angrily. ‘Nothing you say will sway me.’

‘Nathaniel!’ The shout echoed through the chamber, with such force behind it that both of them halted.

Garro looked down at the hand that Voyen had placed on his vambrace, a warning flashing in his eyes. ‘Step back, brother. Now.’

‘Hear me out,’ said the former legionary. ‘That is all I ask.’

‘There is no explanation you can voice, Meric.’ Garro’s ire ebbed, replaced by a sadness. ‘I am disappointed in you.’

‘I have not done this for your approval, my captain,’ Voyen said stiffly. ‘I did it for a greater good. For our battle-brothers and our Legion.’

Garro’s scowl returned. ‘The Death Guard are no longer our Legion. They broke that faith when Mortarion turned against the Emperor.’

‘We can bring them back.’ Voyen’s words gave him pause, as did the light of certainty in his old friend’s eyes. ‘I can bring them back.’

‘With that?’ Garro turned and gestured tersely towards the only object in the hall, a heavy cylindrical cryo-casket made of plasteel and armoured glass. ‘A harvest of poisoned dregs and foul detritus?’

Voyen raised his hands. ‘How does one cure a disease, Nathaniel? First you must capture the virus. Analyse it and conquer it. Only then can a vaccine be feasible.’

The warrior sneered. ‘A vaccine? We do not speak of some malady to be treated by balms and potions! You cannot… recover from this corruption. I have seen it, at close quarters and with my murder in its fangs! I have looked this foulness in the eye and glimpsed the true shade of its hatred.’

‘You are not alone in that,’ insisted Voyen. ‘I was on the Eisenstein too, remember? I know what happened to Grulgor and Decius! I saw the pestilence that overtook their bodies.’

Silence stretched between them. It seemed like an aeon had passed since they had fled to Terra. Garro and Voyen, and Solun Decius, Andus Hakur, Iacton Qruze and the rest of the Seventy, who dared to oppose their primarchs when all loyalty to Terra had been burned to ashes.

In the aftermath, amidst the airless wastes of Luna, they had awaited an uncertain fate. Warriors orphaned by their traitor kinsmen, trusted by few, feared by many. In that silence, their brother Decius had been taken by the same insidious taint that even now was undoubtedly corrupting the rest of their Legion.

Garro had been forced to kill Decius out there in the Sea of Crises, destroying the aberrant creature he had become. And perhaps, in the act, the battle-captain had known that he had been spared for something greater.

Voyen saw something different that day. A sickness that he could not turn away from. The Apothecary surrendered his birthright as a Space Marine and dedicated his existence to finding what Garro now thought impossible.

‘A cure,’ said Voyen. ‘I believe it exists. It must.’

Garro shook his head. ‘No matter how hard you wish for it, Meric, no matter how much either of us would wish it to be true… Believe me when I tell you that it does not.’ His harsh retort robbed Voyen of any immediate reply. ‘Now get out of my way, or I will put you aside by force.’ He pushed past his comrade and strode towards the dais and support frame upon which the casket rested.

‘You cannot know that,’ Voyen called after him.

‘What I know…’ Garro tried to find the words that would convince the Apothecary. ‘What I know is that corruption is absolute. It is subtle and constant.’

‘Do you see that in me, my lord?’

He released a slow, sad breath. ‘You kept something from me once before, brother. Your membership in the lodges.’ At Garro’s mention of the covert gatherings instigated by Horus’ Legion, Voyen hesitated. Guilt soured his expression.

‘I have atoned for my mistake!’ He looked at the deck, chastened. ‘I foreswore that clandestine pact when I learned they were the tool of the Warmaster’s perfidy.’

‘Indeed,’ allowed Garro. ‘But still you kept all of this from me as well.’ He opened his arms, gesturing at the walls. ‘You began your work in secret and hid it from the world. Why? Is it because you knew what I would do when I learned of it?’

‘I did not think you would understand,’ Voyen said hesitantly. ‘I am a man of science, and I think in such terms. But you are…’

‘I am what?’ snapped the legionary. ‘Do you think me a credulous fool?’ He snorted. ‘You know me better than that.’

Voyen eyed his former commander, choosing his words with care. ‘You have always put great stock in the numinous. I believe only in what I can see and touch and know.’

Garro hesitated before the steel-blue cylinder. ‘Aye, I have faith, brother. But that does not mean I have abandoned reason. It is you who cannot see clearly. You cling to the truth you were born with, that this is a rational universe of immutable laws. You tell yourself you could understand all of existence, if only the structure of it were visible to you. But that is not so.’

‘Then what do you say is true?’ There was open challenge in the words.

‘The truth is that we live on the surface of a great maelstrom, populated by powers we can only begin to comprehend.’ Garro had rarely been called upon to frame such thoughts to voice to others, but now he did so, they came to him clearly. ‘That we must oppose those threats unto death, on that point you and I fully agree. But if your only compass is the lucid and the possible, then you have already lost! The Archenemy lies beyond human constructs like reason and logic. To fight them, to beat them, we must see past the veil.’

Voyen waved at the air, as if he were dismissing a nagging insect. ‘If I can save the lives of the Death Guard–’

‘You cannot save their souls,’ Garro broke in. ‘It is already too late for that.’ The warrior studied the container. Through misted, glassy panels, a dark grey mass of particulate matter was visible. It resembled volcanic ash, clumps of it accreting around objects that might have been fragments of mutant bone or distorted chitin.

It was all that remained of the ground where Solun Decius, transformed into a monstrous Lord of Flies, had perished. Where he fell, Decius’ ashen remains polluted the lunar surface like a toxic spill. In any other place but the moon’s magnificent desolation, the residue of death would have spread like a canker. And now that material had been scooped up and gathered here for transit off-world.

Garro glanced at his former battle-brother, unable to mask his dismay. ‘Where did you hope to take this?’

Voyen took a moment to reply. ‘The moon Io, the Jovian installation. There is a facility there that rides atop the sulphur oceans. It belongs to a loyal faction of the magos biologis who rejected the rebellion of Mars. We could examine the remains there, in safety.’

He considered the Apothecary’s use of that last word carefully. ‘How many men died to gather it all?’

‘Seven men perished in the recovery process. Each from a different chimeric disease vector.’ The answer was a reluctant one. ‘They were dead before we could get them to an infirmary.’

Garro frowned. ‘And still you wonder why I came to stop you.’

When Voyen spoke again, his manner was different. Something had changed in him now, and there was almost a beseeching tone to his words.

‘You left us behind, Nathaniel, those who remained of the Seventy. You went away and you were given purpose. But not the rest of us. Not I.’

Somehow, the Apothecary seemed to have been lessened by his experiences. He went on.

‘So I forged my own. We legionaries are functionally immortal, are we not? Away from battle and threat of violent demise we might live for millennia. So I chose to rededicate my existence to finding a cure for that hideous living death that took our former kinsmen.’ He met Garro’s piercing gaze. ‘I need this purpose. Without it, I am only the cast-off son of a Traitor Legion. Lost and forgotten, distrusted and maligned. I have no Knight Errant’s armour, no sanction from Malcador the Sigillite to elevate me. I have only my hope. You understand that, don’t you?’

Garro did, only too well. ‘More than you can know, my old friend.’ He shook his head. ‘And that is why, for the final time, I refuse you. This must end here.’

‘If you do this,’ cried Voyen, ‘then there will be no chance of redemption. You will doom the name of the Death Guard to live in infamy for thousands of years!’

‘It is our gene-father, Lord Mortarion, who made that choice, Meric,’ Garro said sadly. ‘Not I.’

The shadows were at their heaviest here, thick curtains of night-dark that made the wide space of the hall seem enclosed and oppressive. As Garro reached for the casket, he felt the flesh on the back of his neck prickle. That innate war-sense, bred into him through the gene-works of the Legions, came alive. An intuition he could not name, an animal impulse warning him of a danger as yet unrevealed.

His armoured fingers touched the curved lid and he knew that something was amiss. There, along the seam that held the casket closed, the thick brass mag-locks that should have each been sealed tight were hanging wide, the latches like slack jaws.

‘It is open…’

Garro heard the shock in his old friend’s voice. ‘What? That’s impossible!’ But then the low moan of a deathly, unearthly wind blotted out his words.

Suddenly the air tasted of foetor and rancid meat. A wave of slaughterhouse stench and decay arose, potent enough to curdle the air in Garro’s lungs and repulse even a legionary’s constitution. He took an involuntary step backwards, though some instinct made him reach out towards the black, shadow-wreathed stanchions supporting the casket. Light moved strangely upon the iron pillars, almost as if it were being absorbed by the dark, and Garro had the sudden sense that the unnatural shadows he saw were not falling from the play of illumination and shade.

Darkness coated everything in a fathomless slick. His fingers scraped at the metal and encountered thousands of tiny, chitinous forms, clustered so densely together that they were a thick, black mantle.

The shadows were flies.

Hidden in the gloom, the silent, unmoving insects now exploded into horrible, freakish life. Their tiny mutant wings were sharper than razors, their warp-tainted mandibles wet with acidic venom, and they craved warm flesh and spilled blood. The droning swarm rose up and attacked them both in a shimmering black tempest.

‘Back!’ shouted Garro. ‘Get back!’

Voyen stumbled as the cloud of insects writhed and turned in the air. ‘Where did these things come from? There was no living organic matter in the ashes. They could not have come from the casket. This chamber was hermetically sealed. Nothing can get in or out. Nothing!’

‘They came from the immaterium,’ Garro shot back. ‘They are born out of madness and corruption. Do you see now, Meric? This is the nature of the enemy.’

‘The warp?’ The Apothecary struggled to grasp the reality of it.

‘Aye,’ he said grimly, and he shoved Voyen towards the heavy airlock hatch behind them. ‘Go! You are unprotected! These things will feast on the meat of you, make your body a nest for their maggot hatchlings. We cannot let the swarm move beyond this chamber. Go now, and seal the door behind you!’

Garro’s former comrade nodded, but he could not take his eyes off the casket. Of its own accord, the metallic cylinder was deforming, cracking open, and a torrent of newborn insects flooded out, filling the air with a hurricane of glistening wings.

Although he carried no weapons other than Libertas, Garro knew he had to find a way to destroy these things. As if seeing his thoughts on his face, Voyen cried out to him. ‘You can’t fight them with a sword!’

He waved him away. ‘Let me worry about that!’ Voyen stepped over the threshold and Garro slammed his mailed fist into the hatch controls.

The metre-thick barrier of solid plasteel slid into place and locked shut. Garro reached down and donned his sharp-snouted battle helm, securing it against the dithering cloud of carnivorous flies. Through a portal of armoured glass, Garro saw Voyen’s face looking back at him from the safety of the corridor beyond. The Apothecary’s aspect was that of a man shaken by a truth he did not wish to face.

‘I warned you,’ he said, his words distorted by the helmet’s vox. ‘This is what the enemy is capable of. And when we try to fight them on a battleground of reason, they shift the sands beneath us. We are at war with the impossible.’

He marched into the storm of flies, but did not draw his power sword. Voyen was right; even with the weapon’s energy-charged edge, Garro would only destroy a handful of the swarming horde. He had a different manner of attack in mind.

With each step closer to the casket, the density of the flies increased. He heard the scratch and snap of thousands of microscopic fangs biting into the ceramite sheath of his armour. The flies chewed at the flex-joints, trying to pierce to the plasteel beneath. They clogged the breather slits of his faceplate with a wet paste of their own crushed bodies. His helmet’s glowing eye slits drew them in like moths to a flame, blinding him. Step by step, Garro felt his way back to the casket on the dais. A colossal mass of flies crawled and writhed across the plasteel surface, acid venom sizzling from their maws. For a moment, the warrior thought he heard the echo of Solun Decius’ warped laughter in the buzzing of their wings.

He knew what needed to be done. In a way, he had known from the moment Rogal Dorn had handed him that data tablet on board the Phalanx. He blink-clicked an image-icon inside his helmet lenses and opened a vox-channel to a preset frequency. ‘This is Captain Garro. Execute emergency protocol. Open the doors.’ As the words left his lips, he activated the magnetic pads on the soles of his boots, and tensed against what was to come.

The blank bulkhead at the far end of the hall shuddered and then, in the manner of a magician’s trick, it became a series of great panels that shifted on hidden rails, retreating back into the walls. Behind it, a blinding, yellow-orange inferno was suddenly revealed, blazing beyond the retracting doors, filling his vision.

The turbulent surface of Sol, Terra’s great sun, seared him with its incredible radiance.

The tainted atmosphere inside the compartment was immediately blown out into the vacuum beyond, and with it went the creatures of the swarm. The mutant insects were simultaneously flash-frozen and burned to a crisp, and even their warp-tainted origins were not enough to save them from the titanic power of the star.

The screaming air howled around him until it trailed away into the silence of space, and then the only sounds Garro could hear were the internal mechanisms of his power armour and the steady pace of his own breathing. After a moment, soft alarms began to chime, and he felt the withering solar heat even through the dense layers of his wargear.

Crimson warning runes lit up across every read-out visible to the legionary, as the temperature and radiation inside the compartment rose towards lethal ranges. The heat burned off the dead flies and scorched the front of Garro’s grey armour a dull, sooty black. He felt it beat at him, slowly boiling him alive. He had little time to finish what he started. With effort, he reached for the casket and took hold of it.

The intelligence intercepts that Dorn had given him were thorough, as one might have expected of the Imperial Fists. The primarch’s Legion watched all that took place in the boundaries of the Solar System, and it was their agents who had logged and tracked the works of Meric Voyen and the cadre of men from the magos biologis on Io. Dorn’s sentinels looked for anything that carried the slightest suggestion of sedition, and it did not surprise Garro that they made special effort to watch the warriors of the Seventy, the Death Guard battle-brothers who had become lost in the no man’s land between their traitorous kinsmen’s misdeeds and the new oaths sworn by Garro as a Knight Errant.

Even after everything they had done, after all that had been sacrificed, they would never be trusted. The Fists watched them and waited for treason to bloom, even as Garro knew that it never would. It would forever be a weight they would carry, to realise that they would never be able to do enough to erase Mortarion’s betrayal.

So then, what must Dorn have thought of poor Meric’s foolhardy venture? The primarch of the Fists had given Garro permission to intervene personally in this instance, but he had to have known how that would play out. He imagined that the primarch gauged this as some kind of test. The legionary had no doubt that Dorn would not have given him this opportunity without planning in an alternative.

There were warships out there in the void, shadowing them. He had not seen them, but Garro knew Dorn’s ways, and so he knew they were there. Ships with orders to obliterate this vessel and every­thing aboard it, if Garro did not end this today.

The Fists would have seen Voyen’s scheme as dangerous, as a thing to be stamped out and destroyed utterly. Dorn’s sons never chose subtlety where the application of naked force would better serve. Giving Garro the gift of dealing with this on his terms was an act of kindness, in a strange way, but it was also an act with an agenda behind it.

If Dorn knew of Voyen’s desperate, doomed plan to disinter Solun Decius’ warped remains and take them to Io, then so did Malcador the Sigillite. Yet the Regent of Terra had said nothing of it to Garro.

What did that mean? How, in all the complex strata of the Sigillite’s scheming, did this circumstance benefit him? Had Malcador wanted the Fists to terminate Voyen’s experiment? Had he wanted it to succeed? Or had the Regent of Terra known all along that his Agentia Primus would end up in this place, on this ship, standing before a casket filled with death and corruption?

When Garro had intercepted Voyen’s ship out past lunar orbit and forced his way on board, his first act had been to convince the vessel’s commander to divert course and accept no countermand of that order, save from Malcador himself. And as the ship turned away from Io and Jupiter, directly towards the sun, Garro had gone below to find his brother.

He pushed all other questions aside and concentrated on the moment, until nothing lay before him but the blinding oblivion of the great solar furnace, putting his full strength into the action and tearing the casket from its support with a snarl of exertion. He lifted it high, marshalling all the potency of his genhanced musculature and the power armour that encased him, and then he hurled it through the open hatchway and into the void, into the eternally hungry grasp of the star’s gravitational pull.

He watched the blackened, twisted mass of the container tumble end over end, spilling streams of decayed and desiccated matter from within. Dead clouds of chitin glistened in the orange light, and the casket began to break up. Passing into the corona, it would be stripped down to plasmatic gas and absorbed into fuel for the raging fires of the chromosphere, every last molecule of its uncleanness burned and purged from space.

He turned away, chemical sweat streaming down his brow and blinding him. ‘Garro to bridge,’ he told the vox. ‘Close it.’

The shutters silently slid closed once more and locked back into place. The sounds of the world outside Garro’s armour returned by degrees as air rushed in to refill the chamber, and at length he removed his helmet.

He took a wary breath. He tasted the oily tang of burned metal and the ozone of machine-cycled air, momentarily grateful that the foetid stench of decay that had so sickened him before had been completely expunged. ‘It is done,’ Garro said aloud.

Is it done? The question in his thoughts countered, nagging at him.

From the corridor beyond, Voyen saw Garro standing amongst the trace ashes of the burned swarm, and the horror of full understanding at last came to him.

All his hopes to search out a cure for the malaise he had seen in the diseased forms of Ignatius Grulgor and Solun Decius were gone. His fears for the future of the Death Guard, his wish to save his brethren. This need that defined him… It was in vain.

His own eyes had shown him the truth. Garro was right. This new war was a thing of daemonic powers and foul magicks as much as guns and blades, and if that were so…

‘How can a rational soul face that?’ He faltered over the words as a wave of weakness came over him. Voyen felt his throat tighten and a sudden burning in his blood. A stinging sensation made the flesh of his forearm twitch and he pulled back the cuff of his robes, part of him knowing, fearing what he would see.

There, on his skin, was the reddening mark of an insect bite and, already forming, a trio of tiny sores. He thought he heard the tinny, high-pitched buzzing of a fly, and his hand came up to swat at the air around him.

Voyen struggled for breath and turned in place as an alien, unfamiliar sensation filled him. Horror welled up inside like bitter bile. He shot a look back towards the sealed hatch and through the armoured glass panel, the Apothecary saw Garro standing on the far side of the door. His former commander was watching him with a sorrowful expression. Voyen tried to speak, but no words formed.

Garro’s eyes were bleak. ‘Show me,’ he ordered, his words muffled through the thick glass.

Voyen shook his head, raising up his hand, almost as a gesture of warding. He felt the skin on his palm tighten, and he turned it to his face. There were more lesions and puckered flesh there, red and damp and newly formed.

Garro looked away, saying something into his vox-bead. A moment later, Voyen heard the grinding of gears at the far end of the corridor as a thick pressure door emerged out of the deck and rose to seal off the length of the passage where he stood. He looked back towards Garro in time to see his old friend don his battle helmet once more. Then the door between the two of them began to slide open.

The Apothecary reached for his courage and stood his ground.

Rubio found him in the Citadel’s landing bay, surrounded by a quartet of patient gun-servitors, all with their cannons at rest but all in active pre-combat mode.

Garro sat in the middle of the machine-slaves upon an overturned cargo crate, the hard lunar light glistening off his armour. Another work serf was slump-shouldered and inert by his side, dirty with the remains of whatever it had cleaned off the other legionary’s wargear. The stringent odour of powerful chemical purgative agents lingered in the air. For his part, Garro was working at the blade of Libertas, the weapon lying across his lap. With metered, careful motions, he cleaned the sword, dabbing away spots of what could only be dried blood.

Where have you been? Rubio wanted to ask the question, but he hesitated. It was unlike Garro to simply disappear without a word for days on end, and yet that was exactly what he had done, commandeering a Stormbird with no flight plan and no mission at hand.

Instead he asked the question that preceded. ‘What happened to you on the Phalanx?’

Garro looked up at him, then back to the sword’s blade. ‘You know. The mission was a failure. The Imperial Fists Librarian, Massak. I could not convince him to join us.’

‘There’s more to it than that,’ Rubio countered. He sensed the shape of Garro’s surface thoughts, even without having to actively probe his mind. ‘Dorn. Dorn spoke to you.’

‘Stay out,’ Garro said quietly, the warning gentle but no less firm for it.

The psyker tried a different tack. ‘Since you came for me on Calth, over these past months we have grown to respect one another, yes? To share the trust of brothers in battle.’

‘Of course.’

‘But you cannot speak to me of where you have been?’

‘It was a duty,’ he replied, cleaning the blade with infinite care. The naked crystalline-metal edge shone, all traces of spilled blood gone from its surface. ‘One that is complete now. You need not concern yourself over it.’

Rubio hesitated. He knew of no such mission that had come from the Sigillite, but the changing shade of Garro’s aura became marbled with a deep sorrow and suddenly the Codicier felt a stab of guilt, as if he were trespassing upon some private moment.

‘What do you want of me, kinsman?’ The other legionary looked up at him, before returning the sword to its scabbard.

‘Orders,’ said Rubio, nodding to himself. ‘There is news from Malcador’s prognosticators. They predict a brief path will be opening through the Ruinstorm, a treacherous one to be sure, but enough to serve our purposes. It is time. Time to venture out and find the last of them.’

Garro rose to his feet and the gun-servitors flinched in unison, but then after a moment, the machine-slaves seemed to think better of it and they retreated away across the landing bay, their smaller servile cohort trailing behind.

There was an uncountable distance in the other warrior’s gaze, a melancholy that Rubio had sometimes glimpsed but never seen fully revealed until this moment. ‘The last,’ he echoed, and in those words the psyker knew he was counting a cost that would never be repaid. ‘If only that were truly so.’

Rubio found he had no reply to that, so he gestured across the bay to where a fuelled and ready drop-ship sat waiting for them. ‘Command is yours, battle-captain,’ he said, deliberately using the old Death Guard honorific. ‘Give the word.’

But Garro said nothing, only marching away towards the Stormbird.

With each step he took, his grim demeanour shifted until only his resolute and familiar aspect remained.