For four straight Terran days, the fortress had not slept.
Its halls rang with the clang of improvised forges, the scream of cutting tools, the hiss of quenching metal, and the constant bark of orders as soldiers, former laborers, and exhausted PDF survivors worked under Qin Mo's direction. What had once been a battered hab-block was now almost unrecognizable. Reinforced walls rose where thin ferrocrete partitions had stood. Armored firing slits overlooked every likely approach. Hidden logistics passages threaded through the lower levels. Crates of ammunition, charge packs, ration blocks, and medicae supplies were stacked in marked alcoves instead of dumped wherever tired hands had dropped them.
Across the fortress, men hauled newly fabricated weapons into position. Meltaguns were mounted at choke points. Flamers were secured near murder-holes. Heavy stubbers were bolted into firing nests with overlapping arcs. Crude auto-turrets waited in recesses like sleeping predators. Hellgun charge packs were sorted, tested, and stacked according to output instead of Munitorum labeling, because Qin Mo had quickly learned that trusting Imperial paperwork was a good way to die confused.
The place was still ugly. It still smelled of blood, smoke, oil, hot metal, and too many frightened bodies packed into too little space. But it was no longer merely a refuge. It had become a bastion. A hard, deliberate wound in the Underhive's throat.
And Qin Mo had no intention of lingering inside it.
Grey and the five men assigned to him stood near the inner gate, waiting in their newly crafted armor. The suits were not Astartes plate, not ancient relics sealed with incense and ten thousand years of dogma, but human-scale powered armor built for men who had to fight in collapsing corridors, toxic streets, and broken manufactorums. Their surfaces were matte, functional, and stripped of ornament. Reinforced plates protected the chest, shoulders, thighs, and neck. Servo-muscles whined softly beneath the armor as the soldiers shifted their weight. The jump packs mounted across their backs hummed with restrained power, while the integrated gravity shield housings sat between the thruster assemblies like compact iron hearts.
Qin Mo inspected them one final time. Not ceremonially. Practically. He checked seals, power feed stability, emergency release catches, and the alignment of each shield projector. Then he turned toward the fortress exit.
"Move."
Grey obeyed without hesitation. His squad followed at once, armored boots striking the floor in heavy rhythm. Servo-motors answered each step with a low mechanical growl. The sound carried through the corridor like a drumbeat.
"Wait." Klein's voice cut through the noise behind them. "Shouldn't we test these suits first?"
He hurried after them with a small escort of handpicked troopers from the 47th Infantry Regiment. Unlike the workers and wounded men scattered throughout the fortress, these soldiers still carried themselves like professional infantry. Their weapons were clean. Their eyes were alert. Their armor had been repaired where possible and tightened where repair had failed. Klein had chosen them because they were the best men he could spare. He had also chosen them because he clearly intended Qin Mo to take them instead.
Qin Mo did not break stride. "No need."
Klein scowled. "That is not an answer. These are newly fabricated power suits with experimental jump packs and gravitic shielding. I am not asking for a parade drill. I am asking for five minutes to confirm that no one's spine snaps when the thrusters ignite."
"We'll test them in combat."
Grey's mouth twitched inside his helmet. One of his men muttered something that might have been a prayer and might have been a complaint.
Klein stared at Qin Mo's back. "Of course. Battle-testing. Why would we do anything sane?"
Qin Mo glanced over his shoulder. "Because sane procedures require time, proper facilities, and engineers who do not accuse capacitors of heresy."
"Fine," Klein said through clenched teeth. "Battle-testing it is."
He walked beside Qin Mo for several more paces, but his irritation did not fade. It changed shape, sharpening into a more serious concern. His gaze moved from Grey to the rest of the squad. Five men. Five ordinary soldiers. Five survivors from a logistics regiment that should never have been used as front-line infantry.
"Grey's squad are not elite assault troops," Klein said quietly. "The 44th was a logistics and supply regiment. They learned to fight because the Underhive gave them no choice, not because anyone trained them for this kind of operation."
Grey heard him. So did the others. None of them reacted openly, but shoulders stiffened inside armor.
Klein gestured toward his escort. "Take my men. They have actual combat experience. They know corridor clearance, ambush discipline, demolition work, and squad-level assault doctrine. If you are flying seventy kilometers into hostile territory, you should bring soldiers who were trained for it."
Qin Mo stopped. The sudden stillness made everyone behind him halt as well.
He looked at Klein, then at the elite troopers. They were good men. He could see that. Their weapons were held properly. Their spacing was disciplined. They watched the corridor while Klein argued instead of watching their commander. That alone put them above most PDF soldiers Qin Mo had seen.
But they did not know him.
"Grey's team may not be the strongest," Qin Mo said. "They may not be the best trained. But they are the most resolute."
Klein's jaw tightened.
Qin Mo continued, voice calm. "They fought beside me when I had no rank. They followed orders when following me looked insane. They know how I move. They know when to stay close and when to get clear. They know that when I say run, I mean run now, not after asking whether the order violates doctrine."
Grey lowered his eyes for a heartbeat, then straightened. His squad did the same.
Klein exhaled through his nose. He did not like it. Qin Mo could see that clearly. The commander's instincts were screaming at him to argue, to impose a better decision, to replace sentiment with professionalism. But this was not sentiment, and Klein was smart enough to recognize it.
"You are making a tactical choice based on trust," Klein said.
"Yes."
"That is dangerous."
"Everything down here is dangerous."
For a moment, neither man spoke. Then Klein stepped aside.
"Very well."
The fortress exit waited ahead, a slab of reinforced metal folded seamlessly into the wall. As Qin Mo approached, the surface split and withdrew with a deep mechanical groan. Cold Underhive air seeped inside, carrying the smells of ash, sump-water, burned promethium, and distant war.
Qin Mo stepped through first. Grey and his squad followed. At the last second, Klein shouted after them.
"Do not engage the rebels head-on! We are badly outnumbered, and we cannot replace you!"
Qin Mo did not answer. The gate began to close behind him.
It sealed with a heavy clang that traveled through the wall and floor. Klein stood there for several seconds, staring at the shut gate as if irritation alone might reopen it. Then the wall slid open again.
Qin Mo stood on the other side.
Klein blinked. "What?"
"One more thing."
Klein's expression went flat. "Of course."
"In my room, there's a Psyker Suppression Device. Square metal box. Crude casing. Ward-marked control face. If you encounter an enemy psyker, activate it immediately."
Klein's annoyance vanished. "The device that only holds a charge for two days per activation?"
"That one."
"How wide is the effect?"
"Wide enough to matter inside the fortress. Not wide enough to protect idiots who wander outside the perimeter."
Klein nodded once, already adjusting plans in his head. "I'll assign a five-man team to guard and operate it. One officer, two riflemen, one vox-runner, one technician. No one touches it without authorization."
"Good." Qin Mo turned away again.
The wall resealed, smooth and seamless, as if no door had ever existed. Klein stood in silence for a moment longer. Then he looked at the nearest officer.
"You heard him. Five-man guard detail. Now."
....
The new power armor changed the Underhive.
Not the whole Underhive. Not yet. But for the six men wearing it, terrain that would have taken hours to crawl through became something they could cross in minutes. Jump packs flared in controlled bursts, lifting them over collapsed transit tracks, broken manufactorum roofs, toxic runoff channels, and entire districts where the streets had folded inward like crushed metal ribs.
The gravity shields made flight survivable. Debris that should have shredded armor during hard landings flattened or veered away. Sudden impacts bled into the field before reaching bone. The suits were still crude by the standards Qin Mo wanted. Their power systems ran hot. Their joint seals scraped when dust got inside. The jump packs were louder than he liked and drank charge faster than was comfortable.
But they worked.
They covered seventy kilometers in two hours.
Only once did they stop, crouching beneath the shell of an abandoned crane-platform while Qin Mo recharged the squad's power cells. He did it by pulling heat from a burning fuel sump nearby, drawing the flame inward until it guttered blue-white and died. Grey watched the charge indicators climb and decided not to ask questions he was not ready to understand.
The farther east they traveled, the worse the Underhive became.
The fortress district behind them had at least been reshaped by human hands. Out here, war had chewed through everything. Hab-stacks leaned against one another like corpses. Manufactorum chimneys spat intermittent flame into smoke-thick air. Rail lines hung from cracked supports over pits deep enough to swallow armored vehicles. Somewhere below, something vast groaned in the dark as ancient machinery continued working without operators, purpose, or mercy.
Two kilometers from the eastern stronghold, Qin Mo raised one hand.
"Land here. We proceed on foot."
The squad descended in sequence. Thrusters hissed, flared, then died. Armored boots struck cracked ferrocrete with six heavy impacts. Dust jumped around them.
Grey immediately removed a compact recon drone from the side mount on his armor. The device unfolded like a metal insect, its lenses rotating, stabilizers twitching as it woke. With a soft mechanical whine, it rose into the smoke-choked air.
A faint hum entered the squad's comms as the uplink established.
Qin Mo looked toward the eastern horizon, though there was no real horizon in the Underhive, only layers of smoke, metal, and firelit gloom. "Is the stronghold still standing?"
Grey did not answer at once.
Through his visor, the drone feed filled his display. At first, there was only smoke. Dense, roiling smoke. Ash and burning promethium churned together beneath the broken ceiling of the district. Occasional flashes of lasfire strobed within the haze, too brief and scattered to map. The sky above was a rust-red smear of reflected flame.
Grey's throat tightened. The feed looked less like a battlefield and more like the inside of a furnace.
"Use the bio-scanner," Qin Mo said. "That's one of the drone's functions."
Grey snapped back to himself. "Right."
He blink-selected the command, then cursed when the suit failed to interpret the motion properly. He raised one armored hand and manually dragged the icon across his HUD.
The display shifted. Green markers flickered into being across the smoke-obscured terrain. Hundreds. Thousands. They clustered inside a fortified zone ahead, along barricades, trenches, broken streets, collapsed hab-rows, and defensive platforms built into the sides of manufactorum ruins. Red hostile markers swelled around them in dense waves.
A numerical feed populated the lower-left corner of Grey's visor.
[Human forces detected: 5,723.]
[Heretic forces detected: 9,938.]
[Projected attrition outcome: friendly force annihilation in 1 hour, 21 minutes.]
[Estimate provided for tactical reference only.]
Grey inhaled sharply. "The stronghold is still holding."
Qin Mo turned to him.
Grey's voice hardened. "But not for much longer."
One of the soldiers beside him muttered, "Emperor preserve them."
Grey lifted his hand toward the holographic interface, then stopped. "You said these suits could share tactical data. How do I do that again?"
Qin Mo stared at him for one quiet second. Then he sighed.
"Extend your hand. Treat the HUD like it's floating in front of your face. Lower-left corner. Tap 'Combat Mode.' That force-enables squad data sharing."
Grey did as instructed. "This would be easier with voice commands."
"Voice commands are easy to spoof, dangerous under vox interference, and idiotic when everyone is shouting."
"A simple button would be nice."
"You have a button. You just needed directions to find it."
"I'm wearing a coffin with wings and a physics problem on my back. Forgive me if the lower-left corner was not my first priority."
Despite the tension, one of the squad gave a short laugh. It died quickly, but it helped.
Combat Mode engaged.
The drone feed duplicated across every visor in the squad. Tactical overlays stabilized. Friendly and enemy markers updated in real time. Estimated firing lanes, heat signatures, possible armored contacts, and structural hazards populated the display. The system was too advanced for men who had been using standard-issue lasguns a week ago, but fear was an excellent instructor.
Qin Mo looked toward the battlefield. "Now we move."
....
On paper, the numbers were not completely hopeless.
In reality, the defenders were losing. The reason was obvious the moment the drone cut through enough smoke to identify the enemy assault groups.
Aberrants.
Genestealer Aberrants advanced at the center of the rebel waves, hulking mutated hybrids with swollen muscle, misshapen skulls, and limbs thick enough to tear through barricades by brute force. Some carried mining hammers. Others wielded industrial drills, hydraulic cutters, cargo hooks, or lengths of reinforced machinery torn from manufactorum floors. Their weapons were crude only in the sense that falling masonry was crude. They did not need elegance. They had mass, strength, and fanaticism.
Whenever the Aberrants charged, rebel squads launched smoke canisters ahead of them. Visibility collapsed. PDF firing lines broke. Lasgun volleys lost cohesion. Then the monsters hit the barricades, and the battle became close, wet, and personal.
The defenders could kill them. Eventually. With enough concentrated fire. With melta charges. With luck.
But every Aberrant that reached the line bought the rebel infantry time to close behind it. That was how the eastern stronghold was dying. Not all at once. Bite by bite. Barricade by barricade.
Qin Mo and his squad came in low over the battlefield.
The jump packs screamed as they braked. Their descent drove a blast of displaced air across the killing ground, tearing a temporary wound through the smoke. Ash spiraled away. Promethium haze flattened. For a few seconds, the battlefield became visible.
Both sides froze.
PDF soldiers crouched behind shattered barricades, faces blackened, eyes wide, lasguns half-raised. Rebels in stolen flak armor looked up from the charge. Aberrants paused mid-stride, their heavy tools dragging sparks across the ground.
Six armored figures descended through the smoke. The double-headed eagle was stamped across their chestplates.
The defenders saw it first and stared as if reinforcement had become a physical thing. The rebels saw it next and understood that the newcomers were not theirs. For one suspended moment, the battlefield held its breath.
Then an Aberrant stepped forward.
It stood over three meters tall, shoulders hunched beneath slabs of swollen muscle and torn mining harness. One clawed hand clutched the severed head of a human officer by the hair. Blood dripped from the ragged neck stump onto the ground between its feet. Its other hand dragged an industrial hammer whose head was large enough to cave in a Chimera's side armor.
The creature lifted the head, as if presenting a trophy, and fixed its small, hate-bright eyes on Qin Mo.
Its mouth opened. The word came out thick, broken, and full of inhuman hunger.
"Die…"
Qin Mo did not answer it.
He turned to Grey. Grey understood.
For a heartbeat, the young soldier's fear was visible even through the armor. Then he stepped forward, activated his jump pack, and raised his gravity shield to full output.
"For the Emperor!" Grey launched.
The Aberrant roared and charged to meet him, hammer rising overhead. The ground shook beneath its steps. Around them, PDF soldiers ducked lower. Rebels howled encouragement. Grey's squad watched their tactical feeds spike with projected impact warnings.
There were only two possible outcomes anyone watching could understand.
Either the Aberrant's brute strength would win, and Grey's new armor would be crushed around the man inside it like a tin ration can. Or Qin Mo's technology would hold.
The Aberrant never reached Grey.
The instant its body struck the gravity field, the shield's distortion gradient seized it. Momentum did not merely stop. It folded inward. Flesh compressed. Bone shattered. Muscle, organs, and chitinous growths collapsed toward the point of contact under forces the creature's body had no way to survive.
For less than a second, the Aberrant remained recognizable. Then it imploded into a wet mass of crushed meat, splintered bone, and ruptured armor.
Grey passed through the space where it had been, his thrusters re-engaging without hesitation. Blood and pulverized tissue scattered behind him in a red mist.
The PDF line stared.
The rebels stared.
Qin Mo's voice came through the squad channel, calm and practical.
"Confirmed. Shield works in close-impact conditions."
Grey swallowed hard, still moving forward.
"Good to know," he said.
Then the six armored figures hit the rebel line.