Silent detonations blossomed across the periphery of the fleet, colossal blooms of fire illuminating the void before being superseded by a deluge of multi-spectral energy beams. On the command bridges of the Imperial warships, the Navy ratings watched in horror as their auspex arrays shrieked with piercing proximity alarms.
Two months of uneasy tranquility were shattered in an instant.
The veil of the Warp was torn asunder once more as a massive fleet surged into realspace in a textbook broad-front formation. However, it was the heraldry etched upon the approaching hulls that froze the blood of every observer.
"Dark Mechanicum!"
A void-man guarding the tactical monitoring station screamed the identity of the marauders across the bridge. The Imperial vessels, already maintaining a state of high alert, immediately commenced retaliatory fire.
Guilliman, who had anticipated further treachery, narrowed his eyes. The repairs to The Rock had been completed, the other vessels had undergone much-needed refits, and a massive Imperial relief force was even now churning through the Immaterium toward their coordinates. The reason Guilliman and the Lion had lingered in this system was specifically to draw out whatever remaining gambit the Daemon-Demigod held in reserve.
Hellforge-class cruisers unleashed torrents of eldritch Chaos energy, their jagged, nightmarish silhouettes pulsing with the Warp-taint that surged through their armor plating. Desecrator-class battleships banked their massive hulls, their broadside macro-cannon arrays cycling rapidly to hurl volleys of mountain-sized shells toward the Imperial line.
Guilliman signaled the fleet to maintain formation and begin a fighting withdrawal toward the system's edge, intending to keep the enemy locked in a long-range artillery duel.
But the tactical situation did not unfold according to his design.
As the fleet began its maneuver, dozens of Dark Mechanicum vessels moved to pursue. Yet, barely thirty minutes into the engagement, disaster struck the Imperial rearguard. Several Imperial cruisers suddenly veered off course, bringing their primary weapon batteries to bear on their own sister ships.
The sudden betrayal tore a gaping hole in the Imperial formation.
Guilliman immediately attempted to hail the rogue vessels, but they remained vox-silent, seemingly lost to some total internal catastrophe. Having successfully cut off the trailing elements of the fleet, the Dark Mechanicum ships ceased their pursuit of the main body.
Axion watched the screen with a sense of clinical confusion as the Imperial ships ahead moved away while the Chaos fleet closed in from the rear. The legions of the Iron Men had never experienced a sudden battlefield defection; even if their systems were compromised or jammed, they possessed sub-routines to detect and alert the network of such subversion.
Within the bridge-shrines of those betrayed cruisers, groups of Tech-Priests were chanting blasphemous litanies. Chaos energy seeped through the chambers like a physical miasma. Bizarre mechanical apparatuses had been dragged into the rooms, and the bulkheads were now scored with countless shifting, maddening runes.
The power of the Warp saturated the cogitator arrays, beginning the rapid corruption of the ships' Machine Spirits. The priests' own mechanical augmentations began to twist and warp, and even their crimson cowls shifted into darker, more malevolent hues.
As the final syllable of the desecrated psalm was uttered, darkness utterly claimed the fallen Tech-Priests.
"Dark technology leads the future; by the power of Chaos, all things are remade."
The ships underwent a visible, physical transformation as the Warp-taint erupted through their hulls. Thousands of mortal ratings were instantly corrupted, their bodies twisting into grotesque, avian, or multi-limbed horrors. Their eyes glowed with an unnatural light as they raced through the corridors, slaughtering any survivors whose wills remained steadfast.
Caught in the center of this gathering storm, Axion opened a direct link to Guilliman.
"Collaborator Guilliman, is the behavior of these vessels considered standard operational procedure?"
Upon receiving the transmission, Guilliman was presented with Axion's sensor-feed. From that unique perspective, the Lord Regent realized the true nature of the trap.
"Check the positions of every ship in the fleet! Tell me, where is the vessel of the ancient construct?!"
A hololithic starchart flickered into life before Guilliman. The rune representing Axion's ship sat, as expected, at the absolute epicenter of the enemy's encirclement.
Though Belisarius Cawl had once instructed Axion to fire upon sight of the Dark Mechanicum's sigil, the enemy fleet had pointedly avoided targeting the Pectaro. Rather than an assault on the Imperial fleet, this was a surgical operation to isolate and extract a specific target.
Guilliman had been playing a game of grand strategy, trying to bait the enemy into a decisive ambush to flush out hidden threats. But the reality was far more petty, and far more dangerous.
The Dark Mechanicum was not here to hunt the fleet.
Facing the encircled Pectaro, the Chaos Tech-Priests gazed upon the strange, evolving vessel with eyes burning with fanatical lust. On the newly corrupted Imperial ships, the fallen priests looked upon the retreating Imperial fleet with contempt, broadcasting bursts of scrap-code, a digital mockery of Guilliman that lasted for nearly a minute.
It was they who had secretly summoned the Dark Mechanicum.
For two months, these obsessed priests had repeatedly petitioned Guilliman for permission to board Axion's ship to conduct "minor inquiries." Guilliman had denied them every single time. For sixty days, they had watched from afar as the strange vessel at the rear of the fleet transformed. Everything about it defied the laws of the Cult Mechanicus. Its power was an intoxicant; its unknown data was a siren's song.
The Goddess of Knowledge was dancing before them, veiled in mystery, but a "Great Blue Tin" named Guilliman stood in their way. To these zealots, having such knowledge within reach but being forbidden from studying it was a torment beyond endurance. Guilliman had known their desire was dangerous, but he had underestimated its depravity.
He had feared that the Iron Man might inadvertently teach them something catastrophic. No one truly knew what these ancient data-archives would do to a modern mind; not even an Archmagos would dare to audit data from the Dark Age of Technology without extreme caution. The simple weapon schematics Axion had shared were harmless enough, but Guilliman had forbidden any Mechanicus personnel other than Cawl from making extensive contact with him.
In the end, the starving priests made the most ruinous choice possible. Their thirst for forbidden lore overthrew their remaining sanity.
Binary ciphers laden with dark-code were transmitted into the void, and the Dark Mechanicum had answered the call. Their objective was simple: the capture of Axion and his vessel. It was not the grand counter-offensive from Vashtorr or Abaddon that Guilliman had feared. It was a heist of the soul.
As the Dark Mechanicum closed in on the uniquely shaped, gargantuan vessel, they were filled with irrepressible glee. They even went so far as to suppress the Chaos radiation from their own ships to prevent the Pectaro from being prematurely corrupted. After all, once a piece of technology or data is warped by Chaos, it becomes a "black box"—utterly indecipherable and impossible to replicate. Like the crude, "shouted-into-existence" technology of the Orks, it might be powerful, but it is scientifically worthless.
Thousands of boarding harpoons and magnetic cables were launched from the surrounding hulls. The Dark Tech-Priests prepared to breach the ship's control systems, seize the vessel, and drag their prize directly into the Warp.