With the Emperor and Malcador grievously wounded, the primarchs kept as prisoners, and a badly mauled crusade fleet, the short-lived Nexus campaign ended with a practically unconditional surrender of the Imperium. Enough ships and cowed Navigators were captured that there was very little doubt that the Nexus would be able to eventually achieve Warp travel. With the weapons they had, Sev’s threat of entering Imperium space to raze Terra had ensured that negotiations went smoothly for the Nexus Unity.

Magnus felt appalled at how the terms felt both light and oppressive at the same time. After referring to star maps, the Nexus Unity would gain sovereign control over several neighboring systems, establishing a small empire for itself. Sev had promised that the borders would be thoroughly monitored. He also made utterly clear that any unauthorized Imperium presence would be immediately treated as a declaration of war, which would set the Nexus fleet towards Terra, sterilizing every Imperial holding along the way.

Fortunately, the systems around the Nexus Unity were mostly devoid of any other human presence.

Mostly. Unfortunately, the Imperium would have six Terran standard months to have their enroute colony fleets redirected out of the new Nexus territories, or to evacuate those that had just established themselves.

Mechanicum surveyor fleets, outposts and factorums in the region were only given one month, or until the Nexus properly expanded into their new territory, whichever came first. Sev had little mercy to offer the tech-priests.

In the grand scheme of things, the territory carved by the Nexus between Segmentums Obscurus and Ultima had little to affect the Imperium in the end. It was essentially a quarantined area that could be treated no more differently than Warp storms or systems marked as Perditia Extremis. Allowing the Nexus Unity to enforce its strict border controls was barely worth calling an inconvenience.

It was the other half of the terms that Magnus knew was the most dangerous, and the most humiliating.

Beyond the establishment of its empire, Sev would be following the survivors of the Imperial fleet back to Terra, where he would then have free reign to explore and pick out the rest of his war reparations from the archives and repositories in Mars and Terra.

“And by full access, I mean full access. The Library Sanctus, the Noctis Labyrinthus, the Librium Omnis… All doors opened, all archives ready for me to peruse.”

It was either that, or the promise to do unto Mars and the Imperial Palace what had been done to the Nexus’ mirror-Mars. The Emperor bitterly acceded to the ‘tour’. With the captured Mechanicum magi being the most likely source of intelligence, Magnus didn’t doubt for a moment that the Nexus now had a frightening amount of knowledge about the core of the Imperium.

For what little it was worth, Sev at least seemed inclined to make copies rather than outright plundering the Imperium’s precious and forbidden knowledge. Not that it alleviated any of the concerns from the Emperor and Malcador that Magnus clearly felt during the negotiations.

The Crimson King did not know whether to hate the humiliating terms or be grateful that Sev had not been more…vindictive in his terms. The Legions were mostly left untouched, and the Nexus had even returned most of the Luna Wolves’ equipment from the earlier defeat. Every surviving ship was repaired and even slightly upgraded within a few weeks, the crew of mortal humans and Astartes alike being fully healed by the Nexus’ arcane technology. Even the crippled pilots once consigned to dreadnought sarcophagi were now walking amongst their brothers once more, whole of body if not of mind.

Most of the prisoners captured during the one-sided void battle were also returned, shaken but otherwise hale. Magnus noted the distinct lack of Navigators and astropaths among the repatriated crew, and his thoughts soured at the implications of losing those valuable psykers to the interrogations of the Nexus.

On the other hand, almost nothing of the Mechanicum was returned to the Imperium, save for a gaggle of former tech-priests, cowering, wailing men and women that were now fully flesh and blood with their augmentations missing. The more senior priesthood were barely recognizable in their mortal forms, and most had to be constrained and sedated lest they break from their mental trauma. A cursory glance at their minds told the primarch that few would ever truly recover from the ordeal.

The implied insult in the generous actions were far from subtle; Sev and the Nexus Unity saw no threat in the Imperium, enough that it was willing to repair and rearm what was left of their enemies to send them off.

Only the Emperor himself received none of that generosity. Magnus had not witnessed the battle in detail, but he saw the rent in His golden armor, and the healing skin underneath. The damage Sev had dealt to the Master of Mankind was disturbing. Not only was it a clear sign of the Emperor of Mankind’s mortality, it had left a green-tinged void in His psychic form that was barely covered by His blinding psychic radiance.

Neither his Father nor Malcador was willing to speak with him when Magnus tried engaging in telepathic communication. He tasted their bitter resentment, but nothing else.

Two weeks after the Imperium’s defeat, the humbled and greatly reduced fleet finally prepared for Warp travel to begin the humiliating return to Terra. As he had promised, Sev joined the fleet with a captured Ark Mechanicus, now renamed ‘Mekhane’. From what Magnus understood, it had been thoroughly retrofitted with Nexus technology in the short time that the Nexus owned it.

“Mostly to cut out the literal dead meat,” Sev had freely explained to the primarchs when he greeted them aboard Mekhane. “The use of servitors and meat-analogs is utterly inefficient and ineffective. Also purged out the bugged out AI you guys call a ‘Machine Spirit’ and fully sterilized the OS.” Other terms were thrown about, which essentially boiled down to condescending insults against the Mechanicum’s technological advancements.

Only Magnus, Sanguinius and Angron took up the invitation by the Nexus’ ruler for a brief meeting before the translation into the Warp. Or more likely, they were the only ones Sev had invited.

The interior of the Mekhane seemed to have been cored out, leaving a vast space with none of the usual protrusions of consoles, piping, shrines or grates. It was too quiet, devoid of the comforting humming and rolling of cogitator stations or internal wireworks. As Sev led them towards the meeting hall, Magnus felt a disturbing sterility smother out the presence of the invisible tides of the Immaterium. The deeper into the vessel they went, the duller his psychic senses were. Even Sanguinius and Angron noticed it, wearing thoughtful frowns of their own.

Sev finally noticed the primarchs’ reactions about halfway through, and gave a halfhearted shrug. “Ah, forgot about that… It’s the Liquid-T piped throughout the place. A stopgap measure to keep this ship eldritch-free. It’s quick to install, but the liquid state means I can’t fine-tune the rate of siphoning. I’ll have to wait until a proper retrofit to get everything plated down.”

The primarchs shared a look amongst themselves. It was Sanguinius that finally voiced his curiosity. “Is this how you’ve…prepared this ship for Warp travel?”

Sev’s smile was one of excited pride, like that of a scholar eagerly announcing his latest discovery. “Nah, we just upgraded the…Gellar, right? The Gellar shielding tech you guys use for that. Mostly was just streamlining the code and refining the hardware, I’m told. Wasn’t too much of a stretch to incorporate that into our existing defenses either, which is nice. The Liquid-T is like waterproofing the bulkheads, while the upgraded Gellar shielding would be the outer hull itself.”

“How are you piloting this ship then?” Magnus followed up, unable to help himself. “Are you using…your own Navigators?”

“Eh, no. I’m sticking to what I know is reliable. So a warded and fortified navigation program. The initial trials were promising enough to allow for this run.”

Silence descended for several seconds. Magnus reeled in his mind as he picked apart the meanings to Sev’s words. That the Nexus was using soulless machines to manage their navigation through the Great Ocean was ultimately not surprising after all they’ve done. But they’ve already tested the system? When was this done? How was this done that nobody in the Imperium had detected it?

A knowing smirk from Sev was the only answer the primarch was going to get, and he turned to resume leading his guests to their destination.

The meeting hall was austere and as stripped down as every other part of the ship that Magnus had passed. A solid, round table of gray stone and a set of matching chairs - three primarch-sized, one not - were the only things furnishing the hollowed out chamber. Yet, the primarch noted how their footsteps barely echoed at all.

“Now then,” Sev declared semi-seriously once everyone was seated. “To the matter of hand. I’m glad you’ve accepted the invite. I have…offers for each of your legions.” The ruler of the Nexus leaned back in his raised seat, taking on a more informal posture. “Let me get it out of the way first and tell you that the cost will be simple enough. For what I will offer each of you, the price will be simple: A non-aggression pact between your legion and the Nexus, rendered null and void if the Nexus becomes the aggressor in any conflict with your Imperium.”

“You do not trust the Emperor to keep his word?” Angron’s insinuation made Magnus and Sanguinius bristle, though their brother ignored their offense.

Sev shrugged in response. “Consider it a precaution.”

“You must believe to offer much to us if you expect us to abide by this conspiracy,” the Angel said with icy calmness.

Again, the man only shrugged. “I don’t care if you tell everyone the deal I’m making here. Besides…” Sev gave a pointed look that was surely aimed at both Sanguinius and Magnus, “...it’s not like you don’t keep your own secrets as well, right?”

Magnus met his knowing gaze and froze for a half second.

He knew.

The primarch of the Thousand Sons turned to see his brother equally stunned, the shocked surprise marring his angelic features. Curiosity seeped into Magnus’ mind.

What damning secret did Sanguinius of all people hold?

“So, are you all willing to listen to what I have to offer?”

It was both curiosity and dread hope that made Magnus nod in silence, though he couldn’t be sure that the same applied to Sanguinius. Angron at the very least seemed the most eager to accept Sev’s offer.

The World Eaters’ primarch was also the first to follow Sev into a smaller chamber on one side of the hall, and try as Magnus might, neither his posthuman or psychic senses could pick up any of their conversation behind the closed doors. Angron came striding out minutes later with a relieved and satisfied smile on his face, one that seemed utterly out of place on the once bloodthirsty primarch.

Sanguinius was next, with almost imperceptible stiffness to his movements that betrayed his doubts and insecurity. He left the private room visibly shaken, but there too was some of the relief that Angron carried, one that was tinged with shame and guilt.

Magnus forced himself to calmness as he followed Sev into the plain room that barely fit the two of them. As soon as it closed, the primarch recoiled as the man’s eyes glowed in roiling colors, the familiar energies of the Warp spilling out of them.

Sev’s eyes had instantly become the same unbarred windows to the Great Ocean as the Third Eyes of the Navigator psykers. “How-”

The question was cut off, as Sev immediately pitched his offer. “I can prove to you that the current cure for the Flesh Change is a scam. And I can provide you a more reliable alternative, one with no chance of being undone.”

Magnus joined his brothers back in the meeting hall, but he couldn’t find it in himself to meet their gazes. None of the primarchs said anything about their offers as they left the Mekhane, though it felt like Angron was being more empathic about it rather than the guilt or shame his brothers were burdened with.

When he returned to the Photep, Magnus immediately summoned his equerry, along with those commanders present on the ship. He had until they convened to decide how honest he wanted to be with his sons about certain things.

*****

Sanguinius secluded himself in meditation as soon as he returned to the Red Tear. Sev’s offer had been too tempting, and worse, it was so honestly given.

“It’ll take some studying, but I’m pretty sure the Nexus has the relevant tech to come up with an effective cure against the Red Thirst.”

Did he trust the man, who was clearly not just a man, with access to his legion? With potential to irrevocably corrupt or ruin the IXth? But the results on Angron had been clear enough. Even the Emperor, as reluctant as he was, had confirmed Angron’s faculties to be fully restored.

Sev had left the offer open for him to consider, but even now it felt to Sanguinus to be a mistake for not accepting the offer right there and then. But there was still doubt, and there was the disturbing fact that Sanguinius’ prescience had not reared up at all to offer any insight to the path that he might take.

Sanguinius sighed heavily. Regardless, his Father would no doubt question the meeting with the enemy. The Angel decided to distract himself from the heavy choices and focus on preparing himself for the debriefing that was sure to come.