Grey and Grot advanced deeper into the tunnel with steady, practiced precision, their armor moving in heavy, synchronized rhythm while their bio-scanners swept every meter of passage ahead for the psyker Qin Mo required.
The underhive closed around them like the throat of some dying machine. Moisture bled from cracked walls in oily threads. Rusted pipes trembled overhead, coughing steam into the stale air. The tunnel stank of old sewage, hot metal, spent promethium, and the sour rot of places Imperial authority had abandoned generations ago.
Their armored boots crushed debris underfoot: shattered plasteel, corroded grating, broken ammunition casings, and the half-liquefied remains of Genestealer hybrids already burned down by their weapons. Some of the corpses still twitched, alien nerves firing useless signals through bodies too ruined to obey.
After nearly a kilometer of twisting maintenance corridors and collapsed service arteries, Grey's HUD flickered. A new marker pulsed across his augur display. A moment later, his armor's cogitator issued its cold verdict.
[Psychic signature detected. Target marked.]
The words reverberated inside his helmet in a flat machine tone. Grey turned toward the designated point, adjusted the shoulder-mounted plasma cannon over his right pauldron, and braced his stance.
"There," he said.
Superheated light gathered inside the weapon's barrel. The cannon discharged with a violent howl, striking the rusted ferrocrete wall ahead. Stone, metal, and ancient reinforcement mesh glowed white, sagged, and began to run like wax.
Behind him, Grot turned to face the pursuing swarm.
At first, he reached for his graviton hammer. The weapon suited him. Heavy. Direct. Honest in the brutal way only a tool designed to crush things into paste could be honest. But his HUD updated before his hand closed fully around the haft. Red tactical glyphs flared across his visor, outlining the incoming hybrids' clawed limbs and marking their speed, reach, and probable armor penetration.
Melee engagement: inadvisable.
Grot grunted. "Fine. Spoilsport."
He locked the hammer back onto its mount and brought up his heavy scatter-las instead. The weapon's capacitors whined as they cycled.
The xenos tide surged from the gloom.
They came as a writhing mass of warped limbs, chitinous growths, and human features stretched into things that should never have worn human skin. Their claws scraped the tunnel walls with a sound like knives dragged across bone. Their eyes shone in the dark, narrow and hungry, fixed on the two armored figures barring their path.
Grot opened fire.
Las-bolts filled the corridor in a brutal, overlapping storm. The scatter-las did not fire elegant single beams. It vomited disciplined sheets of light that cut through bodies, limbs, skulls, and the rusted metal behind them. Hybrids burst apart mid-charge. Others collapsed as smoking husks, their clawed hands still reaching forward as momentum carried them into the corpses ahead.
Within moments, the tunnel floor became a carpet of charred bodies. Heat shimmered above them. Burned flesh and alien blood filled the passage with a thick, greasy stink that even the armor's filters could not entirely erase.
"These xeno-bastards just keep coming," Grot muttered. His reactor core vented surplus heat through armored exhaust slits, allowing the scatter-las to cool between volleys.
Grey's plasma cannon fired again, widening the half-melted breach ahead. "You could always let the gravity shield pulverize them."
"I could," Grot said, sending another burst into a cluster of hybrids crawling over their dead. "But then why the hell did we mount weapons on this armor?"
Grey smiled despite himself. "A fair theological question."
The plasma cannon discharged again. More ferrocrete sloughed away, revealing a cramped service void beyond the wall. Grey stepped through first, his armor scraping sparks from the molten edge. Grot followed backward, still firing, until the last visible hybrid dropped twitching into the dark.
By now, the fighting had become routine in the worst possible way. Advance. Scan. Burn through obstruction. Kill whatever lunged from the dark. Repeat. The enemy remained lethal, but their pattern had grown familiar enough that the two men found room for conversation between bursts of violence.
"Didn't the squad try to convince you to ask the Lord Commander to name our armor?" Grot asked.
Grey sighed. "They did."
"And?"
"He called it 'Armor.'"
Grot paused long enough to turn his helmet toward him. "That's it?"
"That was my reaction."
"No title? No pattern name? No glorious line about thunder, wrath, iron, death, or the Emperor's boot?"
"I pressed him for something better." Grey stepped over a severed claw and adjusted his scanner sweep. "He became annoyed and called it Thunderborn-Pattern Power Armor."
Grot gave a slow, grudging nod. "Now that has weight."
"I suspect he made it up to end the conversation."
"Doesn't matter. Thunderborn sounds better than Armor."
"Everything sounds better than Armor."
Another cluster of hybrids emerged from a side passage. Grot erased them with a short burst before they crossed ten meters.
"Thunderborn it is," he declared.
Grey did not argue.
...
After another relentless half-hour, the tunnel opened into a vast underground cavern.
The space had once been part of some industrial hollow beneath the hive: a loading basin, perhaps, or a collapsed transit reservoir. Now it had become a battlefield. Corroded support columns rose into darkness. Broken catwalks hung overhead like snapped ribs. Pools of chemical runoff reflected weapon flashes in sickly colors.
Grey's HUD erupted with alerts. Multiple hostile signatures. Entrenched positions. Heat blooms. Weapons tracking movement.
He scanned the cavern in a heartbeat. Dozens of cult infantry had barricaded themselves behind scrap walls, overturned cargo frames, and welded machine housings. Lasguns and solid-shot weapons were already aimed at the breach. Their equipment was crude, but their firing lanes were not. Someone had placed them carefully.
Lasguns. Stubbers. Autoguns. Makeshift barricades. Firing slits. Kill zones.
At the far end of the cavern, separated from the cult line by a scatter of corpses and wreckage, stood one lone Imperial soldier.
Grey recognized him immediately.
Albert.
The man faced two cult infantrymen with a stolen xeno blade in his remaining hand. His swings were weak, desperate, and slowing. Blood poured from the ragged stump where one arm had been severed. His armor was split. His legs trembled. Yet he remained standing, baring his teeth through pain as if spite alone could keep his heart beating.
This was not a battle.
It was an execution taking too long.
Grey's mission was not to save Albert. The objective was the psyker. Still, he was not opposed to saving the man if the opportunity presented itself.
The opportunity depended on completing the primary objective first.
Behind the entrenched cultists, two robed figures stepped into view. Their garments were filthy and torn, but warp-energy crawled around them in unstable pulses, making nearby dust lift from the ground and drift in unnatural spirals.
Two psykers.
Only then did Grey understand the earlier scan. The psychic signatures had overlapped, blending into one marker until proximity separated them.
One of the psykers raised a trembling hand and screamed, "Fire!"
The cavern erupted.
Las-bolts and kinetic rounds tore toward Grey and Grot in a converging storm. Muzzle flashes strobed behind the barricades. Solid-shot rounds hammered into the air around them and lost all meaning against the gravity fields. Lasfire splashed across armor plating, leaving brief scorch marks that vanished beneath cooling vapor.
Neither man flinched.
Grot deactivated the wide gravity shield and drew his graviton hammer. Grey raised his heavy scatter-las.
His HUD completed the calculation almost instantly.
[Tactical calculation complete. Estimated time to eliminate entrenched hostiles: 2.3 seconds.]
Grey fired.
The scatter-las roared, sweeping across the barricades in a disciplined arc. Cult infantry vanished in bursts of light and blood. Scrap walls glowed, buckled, and collapsed. Weapons detonated in their owners' hands. A heavy stubber team had enough time to turn their heads before the beam punched through the gun shield and reduced all three men behind it to burning fragments.
Grot launched forward.
His jump pack ignited with a controlled thunderclap, hurling him across the cavern in a low, brutal trajectory. The graviton hammer came off his shoulder mount and into both hands.
One psyker reacted first. His fingers crooked, and twisted metal tore free from the cavern walls. Pipes, support braces, and jagged sheets of plating screamed through the air and smashed into Grot's armor. The impacts did not pierce him, but they struck hard enough to halt his momentum mid-leap.
The second psyker thrust both arms forward. Warp-fire gathered between her palms, green-white and hateful, then streaked toward Grot like a living inferno.
Grot's armor shrieked warning runes. He ignored them.
"I AM THUNDERBORN, YOU WARP-SCARRED WHORE!"
His jump pack surged to maximum output. Grav-motors strained. The telekinetic bind buckled under brute force and overbuilt engineering. Grot tore free, dropped through the incoming warp-fire with his armor smoking, and crashed into the first psyker like a falling bunker.
The graviton hammer fell.
The psyker ceased being a man.
Bone, meat, robe, and warp-tainted flesh burst outward in a wet crimson smear that splattered across the cavern wall and rained down over the broken barricade behind him.
At the same moment, Grey extended his augmetic arm.
The grav-field manipulators built into the limb flared. The second psyker's eyes widened as an invisible force seized her and ripped her from behind the cult line. She flew across the battlefield, limbs flailing, robes snapping around her like torn banners, and slammed into Grey's waiting grasp.
His augmetic fingers closed around her throat.
She tried to scream. Only a strangled rasp came out.
Warp-light gathered in her eyes. Her lips twitched around the start of a curse. Then the anti-psyker dampeners embedded throughout Grey's Thunderborn armor activated fully. The air around him tightened. Hexagrammic fields and engineered suppression harmonics bit down on the psyker's connection to the Warp.
The light in her eyes died.
For the first time since she had entered the cavern, she looked truly afraid.
She clawed at his hand with both of hers, heels scraping against his chestplate, but Grey's grip did not shift. Her struggles weakened as air failed her. When her movements slowed to useless spasms, he loosened his hold just enough to keep her alive.
The fight was over.
...
Grey crossed the cavern to Albert.
The soldier had fallen during the exchange. He lay on his back amid blood, rubble, and the remains of the two cultists who had tried to finish him. The stolen xeno blade had slipped from his hand. His face was pale beneath grime and dried blood, but his mouth held the faintest trace of a smile.
Grey knelt and ran a bio-scan.
His HUD mapped the body in cold clinical lines: severed limb, catastrophic blood loss, organ failure, no meaningful cardiac activity. A final diagnostic appeared across the display.
[Exsanguination. Survival Probability: 0%.]
Grey stared at the line for a second longer than necessary.
"He's dead," he said.
"Yeah." Grot's voice came quieter than usual. He looked down at Albert's face and exhaled through his helmet's vox grille. "Looks like he saw the bastards die before he went."
Albert's smile made that easy to believe.
Grey rose and swept the cavern with his bio-scanners. A few cultists still breathed beneath wreckage or behind broken cover. None survived the next twenty seconds. Grey killed them with short, economical bursts while Grot stood guard over the captured psyker.
When the scan finally showed no remaining hostiles besides their prisoner, Grey turned back.
"We cannot leave his body behind," he said. "Secure him for transport."
Grot said nothing. He only knelt, lifted Albert's mutilated corpse with unexpected care, and locked the body across his armor's carrying frame.
The captured psyker watched them with wide, bloodshot eyes. Her throat was already bruising beneath Grey's grip.
"Move," Grey ordered.
...
Their retreat was not unchallenged.
The Genestealer hybrids they had bypassed, outrun, or failed to fully exterminate had gathered behind them in the tunnel network. They came en masse now, flooding side passages and maintenance shafts like a living infection working its way through the hive's metal veins.
This time, Grot took point. Albert's body was secured across his armor, one dead hand hanging limp against the Thunderborn plate. His shoulder-mounted cannon tracked ahead, cycling through firing modes as hostile signatures appeared through smoke, heat, and broken walls.
He fired.
Devastating energy beams cut through the claustrophobic corridor. Hybrids vanished in white-hot flashes, bodies vaporized before they could leap. The weapon's focused output carved through armor, chitin, bone, and rusted wall plating with far greater efficiency than hammer or scatter-las. Entire knots of abominations were reduced to steam and ash before their claws touched the floor.
Grey followed behind, one hand gripping the half-conscious psyker by the back of her robe, his augmetic fingers locked firmly enough to remind her that survival depended on obedience. His other arm remained free, weapon ready, scanner active.
For long stretches, neither man spoke.
The silence inside the tunnel felt heavier than the gunfire.
Grot was usually loud after battle. He cursed enemies, mocked danger, laughed at poor engineering, and filled dead air with the stubborn noise of a man refusing to let fear settle. Now he walked in silence, his thoughts turning inward despite himself.
Albert had been a soldier in ordinary wargear. Praetorian-pattern kit, maybe improved by Qin Mo's standards, but still nothing like Thunderborn armor. A man with courage, a weapon, and too little protection against horrors that could tear open bodies and armor alike.
Was that the only real difference between him and Albert?
Armor?
Had Grot survived because he was better, stronger, braver? Or because Qin Mo had wrapped him in enough engineered miracles that the underhive's nightmares broke against him instead of cutting him apart?
He did not like the question. He liked the answer even less.
Grey's thoughts ran along a different path.
He could feel the weight of his augmetic arm. The precision of it. The strength. The anti-psyker systems humming beneath the plating. Useful. Effective. Not enough.
Armor could fail. Power could drain. A field could collapse under the wrong pressure. A man who depended entirely on a suit was still vulnerable when stripped from it.
If he improved himself further, if bone, flesh, nerve, and machine were made into something harder to break, then perhaps he could keep fighting even without armor. Perhaps the next Albert would not die in a cavern because one limb was lost and blood decided the matter.
The thought should have disturbed him.
Instead, it felt practical.
At last, the extraction shaft appeared ahead, a vertical wound cut through the hive's infrastructure and reinforced by Qin Mo's drones. Grey checked the upper approach. Clear. Grot fired one final beam into the darkness behind them, collapsing part of the tunnel and burying the pursuing swarm beneath molten ferrocrete.
They emerged from the shaft into the stale air of the extraction zone.
The transport waited with engines hot, its landing struts locked against uneven ground. As they boarded, Grey secured the prisoner. Grot laid Albert's body down with more care than he had shown most living men.
The ramp sealed. Thrusters engaged.
The transport lifted away from the underhive darkness and carried them back toward the 47th Regiment's fortress.