Warhammer 40K: System Error, I Summoned the Arch-Traitor!

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As the ground war on Iax ground forward, Guilliman's forces finally reached the Psuchalina Barbican.

The ancient fortress, once a jewel of Imperial architecture, had become the rotten heart of Nurgle's dominion on this world.

At least ten thousand Death Guard held the walls. They stank of plague and rot from a hundred meters away.

These sons of Mortarion had always been renowned for their endurance. Grandfather Nurgle's blessings had made them worse. Their bodies had swollen to grotesque proportions, bloated flesh split by festering sores that wept dark green pus without stopping. They didn't feel it. They considered it an honor.

Alongside them stood swarms of Nurgle daemons, daemon engines that rumbled like angry machines digesting themselves, and the things the defenders called Mountains — if that word still applied. Colossal mounds of writhing, heaped flesh that moved along the line in slow lurches, each exhale spraying spore clouds dense enough to corrode ceramite.

It was a formidable wall. It held for a while.

Then Guilliman and Horus retasked the battle.

Armored clusters reorganized. Heavy artillery in the rear dialed in their firing solutions.

One order.

The iron tide drove forward like a spearhead and punched through three Death Guard defensive lines without stopping.

The classic Luna Wolves spearhead tactic.

Watching from the rear, Kaelen exhaled slowly.

But command was only one part of it.

The ones who actually broke the line first, who drove into Mortarion's sons at the point of the spear, were two other primarchs: Clone-Fulgrim and Konrad Curze, with the four Battle-Automata Kaelen had loaned them running at their flanks.

The army's heavy firepower wasn't doing much against the Nurgle-blessed the Death Guard. These were Mortarion's sons. They'd been hard to kill before the blessings, and now they were thick enough that bolter rounds hitting center mass disappeared into the rot like stones into a bog. Shell fragments buried themselves in necrotic flesh and accomplished nothing. The Death Guard didn't even register the hits.

Calling them plague hogs was being generous.

Unfortunately for them, they'd run into two primarchs who didn't need guns.

Every time the Phoenician's blade descended, a Death Guard head came with it.

Clone-Fulgrim moved through the enemy like a man performing a kata he'd practiced ten thousand times. His blade traced arcs in the toxic air, each cut landing precisely in the gap between armor plates, through the seam, through the weak point. Clean. Efficient. Nothing wasted. His purple cloak snapped and turned in the poison mist, silver hair catching the light with every pivot.

The Lord of the Night was something else entirely.

Konrad Curze wielded both Lightning Claws the Emperor of Mankind had personally given him, and whatever those weapons touched died and stayed dead. Plague Marines torn apart by those talons did not rise. Nurgle daemons shredded by those claws did not reconstitute. The Emperor's blessing ran through the weapons like a current that simply erased what it touched. Chaos-spawned things had no answer for it.

The four Battle-Automata kept pace, filling in between engagements with precise fire support. Ancient constructs from the Dark Age of Technology, they didn't fatigue, didn't hesitate, and didn't miss. They cleared both flanks of the chaff that might otherwise have dragged the primarchs down.

Sevatar had tried to keep up with his gene-father. He couldn't. The Lord of the Night moved like a bat threading through shadow, no fixed line, no readable pattern. Nobody could track him.

In the rear, Guilliman and Horus coordinated the armored push, steadily widening the breach Clone-Fulgrim and Curze kept tearing open. Impulsors and Gladiators and Astraeus grav-tanks roared through with Astartes drawn from twenty Chapters. Artillery hammered in grids, working the pocket systematically, eliminating everything sector by sector.

The tactical picture was clean. The strategic picture was cleaner. Guilliman and Horus's actual intent was total encirclement: swallow every Plague Marine Mortarion had committed to the Psuchalina Barbican in one bite, leave nothing behind.

"He wants redemption."

Cullen stood at Kaelen's shoulder, observation equipment trained on that purple figure cutting through the far end of the enemy line.

Kaelen set down his optical telescope and nodded. He'd seen it clearly through the lenses. Clone-Fulgrim in the thick of the enemy, his sword moving like it had its own intentions. Purple cloak catching and releasing in the poisoned air. Silver hair sweeping bright arcs with every turn. The blade in his hand wasn't a weapon anymore. It was something between a weapon and a living thing.

"The original committed the sins. He carries the debt." Kaelen watched for another moment, then exhaled. "He has to pay it down, or he can't live with himself." He shook his head slowly. "Worthy of the Phoenician. That swordsmanship isn't combat. It's a dance."

He didn't have better words than that. "Magnificent" was already the ceiling of what he could offer.

And it was earned. Every movement the Phoenician made was precise to the millimeter, and somehow still fluid, still graceful, like a symphony scored for a blade. This was what the Third Legion had been before corruption swallowed it. This was the true bearing of the Phoenix of Chemos.

A boom rolled across the sky.

Kaelen and Cullen looked up together. A ground-assault landing craft bearing the Emperor's Children's insignia was diving toward the surface. Then another. Then more. Their hulls were painted over with Slaanesh's marks, and their approach vectors were wild, almost theatrical, like they wanted to be noticed.

They weren't landing here. Further back, away from the fighting.

"My fallen brother has arrived."

Kaelen hadn't heard him approach. Horus was simply there, standing at his side — the Warmaster's massive frame like a silent mountain in pearl-white armor, eyes tracking the descent of those craft, a thin, cold smile at the corner of his mouth.

"I assumed he'd go straight for the front line," Kaelen said. "Land right in the middle of it. Challenge the clone to a duel."

"Don't forget, my friend." Horus's voice was low and measured. "We are here. Four primarchs. Fulgrim is many things, but he's not foolish enough to challenge all four of us directly. He'll go to Mortarion first. Join forces with the Death Lord before he makes his move."

He paused.

"The fleet has engaged the Emperor's Children fleet. I've also received word from Loken."

"Good news, my Wolf God?"

"Very." A note of pride crept into Horus's voice. "He successfully boarded the Pride of the Emperor. Destroyed the engine room. Crippled her completely. She's drifting in the void now. Dead metal."

Kaelen nodded.

The significance of that was hard to overstate. A Gloriana-class battleship taken out of the war, a class impossible to replace or rebuild. One fewer of those in the enemy's arsenal meant something real in every engagement to come. The Imperial fleet would feel the weight of it lift for the rest of this war.

"Stay in the rear when it starts, my friend." Horus drew a long breath and let it out slowly. The faint smell of machine oil and metal drifted from his armor. "Guilliman, Curze, Fulgrim, and I will deal with our two fallen brothers. We end this ourselves."

Kaelen thought about it for a moment. He knew how this ended. The Emperor of Mankind would arrive when the time came. If things turned against them before that, he could act. Until then, the stage belonged to the primarchs.

"Alright. Watch yourself."

The void battle ended in Imperial victory quickly after that.

Captain Loken had gutted the Pride of the Emperor from the inside, cutting through the power transmission systems and leaving the once-proud Gloriana drifting without propulsion or maneuvering capability, a stationary target in the dark.

He'd also given Lucius the Eternal a proper beating along the way.

The other Emperor's Children he'd encountered had not been so lucky.

With that done, Loken pulled back to his own ship and ordered concentrated fire. The fleet's macro-cannons tore the Pride of the Emperor apart plate by plate. Ten thousand years of the Third Legion's glory and corruption had sailed aboard that hull. It broke apart in the fire, slowly, then all at once.

Simultaneously, the Macragge's Honour broke off from the engagement and climbed back to low orbit over Iax.

On Guilliman's order, the Gloriana fired a single magma bomb, its casing packed with the ashes of an Untouchable.

The bomb punched through the atmosphere and hit the heart of the Psuchalina Barbican dead center.

A mushroom cloud climbed into the sky. White light ate everything.

The Untouchable's ashes rode the shockwave outward, hammering a suppression field into the warp. The Plague Marines who had relied on Nurgle's blessings to shrug off the nuclear detonation had no answer for this. It annihilated them.

The heat killed every enemy inside the encirclement. A very small number of Imperial warriors who hadn't cleared the zone in time died with them.

When the cloud finally dispersed, four figures stood on charred ground.

Guilliman and Horus walked forward into the blast wasteland, weapons in hand, reuniting with Curze and Clone-Fulgrim amid the blackened earth and shattered vehicle wreckage. In the distance, the nuclear afterglow still stained the sky a deep red, an open wound smeared across the face of this dying planet.

Guilliman raised his vox-casters to maximum amplification. The words hit the desolate ground like a thunderclap.

"Mortarion!"

"Brother! You wanted to fight us? We are here. We came because you challenged us. Show some courage and face us. You wanted this. So do we. Let us settle this the way brothers should!"

The smoke and toxic gas thinned and blew back from around the four primarchs, baring the scorched earth and the wrecked husks of war machines around them.

Mortarion didn't appear.

"Think he's too scared to come out?" Curze offered, timing impeccable as always. That pale face split into a thin, mocking smile. His Lightning Claws trembled faintly at his fingertips, still hungry.

"Stay sharp, Konrad."

Horus's voice was flat and hard. He gripped the new Worldbreaker warhammer the Emperor of Mankind had given him. "Mortarion may be watching us right now. So may our other fallen brother."

5 minutes.

10 minutes.

Nothing.

The Imperial warriors in the rear were getting anxious. Four primarchs alone in no-man's-land, and if Mortarion and Fulgrim hit them from an unexpected angle, there was no good outcome to that scenario.

The four primarchs at the front were enduring their own kind of suffering. The waiting kind. Their senses stretched across the wrecked ground, tracking every shift in the wind, every curl of drifting toxic mist. Nothing came.

Then a voice cut through from somewhere in the rear battle lines.

Not loud. But clear. Somehow it threaded through all of it, through the noise and the distance and the formations stacked between the speaker and the front, and landed in the ears of four primarchs and a great many Imperial soldiers at once.

It was Kaelen.

"Mortarion! You First Captain of the Death Guard! You're not fit to face these primarchs — they are the true lords of their Legions!"

The shout hung in the air for a beat.

Then came the second line, harder.

"Send out the real lord of the Legion! Send out Typhus!"

Two sentences. More effective than everything Guilliman's prepared speech had accomplished.

The moment the words landed, dark green mist boiled up from the center of the battlefield without warning. It carried the stench of rot and death, and wherever it spread, the ground curdled and the air thickened to something barely breathable.

A tall figure walked out of the mist. Insect wings rising from his back. Each footfall left a corroded print in the earth behind him.

Plague moved with him like a living thing. Not just the ground and air. The bodies of the Imperial dead lying across the field dissolved under the emanation rolling off him, bodies collapsing into spreading pools of putrid liquid.

Mortarion.

The Death Lord had finally come.

All four loyalist primarchs tightened their grips on their weapons at the same moment.

Their brother still wore that distinctive gas mask. They could feel the fury burning behind it anyway.

Mortarion's insect wings beat slowly in the toxic mist. His great scythe caught the poisoned light, gleaming cold and green.

"WHO SAID THAT?!"

➤ Next: Battle Among the Primarchs

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