The position where Axion hurled the explosive was still over a hundred meters from the trans-dimensional conduit's aperture within the hall.
The weight of the device was staggering; unless one possessed sufficient space to generate momentum or a means to launch it like a macro-cannon shell, depositing it directly into the conduit was an impossible feat for a mortal. Through the sharpened kinetic perception of their superhuman vision, the Astartes clearly saw the timer: a mere five-second countdown. As it tumbled through the air, they watched the runes flicker and bleed away.
In the moment Axion released the bomb, his form blurred, flickering forward in a micro-warp shunt to bridge the gap. He reappeared instantaneously, striking the device to grant it a seamless second burst of acceleration.
Within the hall, the Aegis Protector caught the bomb with preternatural precision, acting as a living railgun to hurl the payload deep into the throat of the trans-dimensional rift.
Thump.
A dull, heavy impact echoed through the warp-space interface—the sound of something massive attempting to emerge from the other side, only to be violently bludgeoned back into the void.
The conduit's aperture began to contract violently, shriveling away into nothingness.
Archmagos Cawl, who had been remotely monitoring the progress from his command sanctum, shifted his multi-lens gaze toward the Necron Tomb Ship looming in the void. A blinding surge of emerald energy erupted from the heart of the xenos vessel. The monolithic structure atop the ship, the Great Tombstone, vomited forth torrents of light as malevolent green lightning arced across its hull.
The bomb had not reached the Tomb Ship's interior; instead, it had detonated prematurely within the trans-dimensional tunnel itself. Cawl observed no thermal bloom characteristic of a melta explosion, nor the "green firework" display he had calculated.
Instead, the catastrophic energy backlash overloaded the portal's stabilizing arrays. Raw, unbound power bled from the Necron vessel's power cores in a frantic overflow.
None could say for certain what occurred within the claustrophobic confines of that Tomb Ship. They only witnessed the jagged arcs of emerald lightning dancing wildly through the vacuum. Then, before the Imperial fleet could react, the Necron ships accelerated with impossible velocity, vanishing into the lightless depths of the sector.
The inertia-less drives of the Necrons, capable of traversing the materium at the speed of light, were beyond the reach of the sub-light pursuit of the Imperial Navy. Furthermore, the Nephilim Sub-sector remained shrouded by the xenos' uncanny null-field, rendering warp travel within its borders an impossibility. Even a mind as bold as Cawl's would not dare a reckless plunge into those stifling depths.
On the planet below, the gargantuan Blackstone pylon still stood, its beam of green energy piercing the heavens.
There was no time left for study. The Necron fleet had already savaged the Imperial task force, leaving the surviving vessels crippled and bleeding. Should reinforcements from another Dynasty arrive, the survivors would be slaughtered.
Even Cawl's massive Ark Mechanicus had sustained grievous internal trauma. The "mind-cleansed" crew members had inflicted significant sabotage upon the Ark's systems, and the earlier Necron boarding actions had left a sixth of the vessel in ruinous condition.
Cawl looked upon the Blackstone obelisk on the planet's surface and let out a sigh of clinical regret. Moments later, a Two-Stage Cyclone Torpedo was unleashed from a Mechanicus battleship holding station near the world.
For this barren, spent husk of a planet, the decree of Exterminatus was a logical necessity. Roboute Guilliman was watching from the bridge of the Dawn of Fire; Cawl knew that with a simple authorization record from the Primarch, even the Inquisition would find no grounds for censure.
This scorched-earth protocol was the only way to ensure the Necrons could not return to reactivate these massive Blackstone arrays. The Imperium could not hold this ground, not yet. Once a breakthrough was secured, the priority was destruction; there would be time enough in the future to return and harvest the secrets of the xenos.
An explosion, visible even from the depths of space, blossomed across the world. The pillar of emerald light that had reached into the stars was snuffed out.
Without waiting to survey the wreckage, every ship in the fleet came about, turning their prows toward the sector's edge to engage their warp drives. With the Blackstone nodes shattered, the empyrean began to bleed back into reality. Though the Warp remained thin and sluggish, the crucial factor was the ability to tear the veil of realspace once more.
Survivors likely remained aboard the hulking wrecks drifting in the void, but a search and rescue operation was a luxury they could no longer afford. Perhaps, in time, a cruiser or two could be dispatched to scavenge the remains, but to linger now was to court death. The Necrons, having been blooded, would inevitably counterattack. Neither Guilliman nor Cawl would gamble the fate of the fleet on such odds.
Reports gathered a month later from the few rescued survivors would confirm the wisdom of this haste: mere seconds after the fleet translated into the Warp, a second Necron fleet, far larger than the first, arrived in the system.
The xenos showed no interest in the drifting Imperial hulks. On the planet below, the Two-Stage Cyclone Torpedoes had turned the crust into a churning sea of magma. The world was geologically unstable, its surface a roiling nightmare where the Necrons could find no stable foundation to rebuild their pylons. Finding the world devoid of strategic value, the xenos fleet departed as abruptly as it had arrived.
The remaining survivors endured a harrowing month amidst the wreckage, sustained only by the fact that the Necron harvesters did not return to finish them.
…
By the time the Ark Mechanicus and the Dawn of Fire led their battered flotilla out of the Warp and back into the materium, they were on the threshold of Ultramar.
Alerted by astropathic distress bursts, the Tetrarchs had mobilized a fleet to assist the crippled Imperial vessels. Cawl's Ark Mechanicus acted as a tug, hauling the broken remains of the Adeptus Mechanicus battleships in its wake.
Merchant convoys and civilian vessels stood in silent awe as the scarred procession passed. Of all the ships, only the Dawn of Fire remained untouched; the others were charnel houses of twisted metal. Arcs of erratic electricity leapt across rent armor plates, and some vessels lost power entirely before they could reach dock, drifting as dead hulks until they were taken under tow toward the nearest starport.
Yet, the most profound damage lay hidden within Cawl's Ark Mechanicus.
Though Cawl had held the ship together through sheer force of will, aided by his Mech-Throne and the vessel's Machine Spirit, the toll was catastrophic. Of all the ships struck by the "Tombstone" pulse, the Ark had been the most heavily populated. The sheer destructive capability of the frenzied Skitarii within had been devastating.
One-third of the Ark's interior had been dismantled or destroyed by its own defenders, exacerbated by the Necron boarding parties. The internal control structures for the Nova Cannon and the majority of the weapon batteries were melted slag.
By Cawl's own estimation, a full restoration of the Ark would require a return to the forge-fanes of Mars. The projected repair time: upwards of one hundred Terran years.