At the close of the 41st Millennium, the Chaos forces in the vicinity of the Eye of Terror grew increasingly rampant. Large numbers of Heretic Astartes fleets secretly slipped out of the Warp. Although the Imperial Navy intercepted and sank many of the vessels, the surviving Chaos fleets continued to wreak havoc across the Cadia Sector.
"A multitude of Imperial Worlds fell under attack, and the Imperial Navy was locked in a constant struggle against the enemies of Mankind in this region. It was then that a terrifying vessel appeared in the sights of our scanners. It was the Plagueclaw, a vessel dedicated to Nurgle..." Alexei suddenly stopped speaking and remained silent for a long time.
"And then?" Tokira asked Alexei. The Scythes of the Emperor's home world was located far across the galaxy in the Ultima Segmentum; the vast distance had prevented them from receiving these reports in real-time.
"Then, the Imperial Navy squadrons sent to pursue them were ambushed by Nurgle's herald, Typhus. This ambush almost completely annihilated the Imperial fleet. Their defeat allowed Nurgle's rot to spread unchecked to the surrounding systems..."
Alexei looked at the distorted reality of the Warp beyond the observation window and spoke in a deep, resonant voice. "These plagues can transform living souls directly into Poxwalkers. They have dismantled the order of countless worlds. This is the 'Plague of the Unbeliever'—the first herald of a full-scale Chaos invasion."
His voice echoed through the hushed command center. After hearing this, Tokira remained silent for a long duration before asking, "What reinforcements do we have besides ourselves?"
Alexei did not answer immediately. The question brought to mind the betrayal that should have already taken place on the surface of Cadia. "Few..." he murmured. "Hopefully, they can hold the line."
As Alexei had predicted, not long ago, millions of Volscani Cataphracts had landed at nearly a thousand landing zones in Tyrok Fields. These warriors, considered among the most resilient in the Cadia Sector, were welcomed as heroes. Even the Cadian High Command was present to show their respect for these vital reinforcements.
However, when the first scream rang out, the assembled crowds were stunned. No one understood the gravity of the situation until they saw the "heroes" of Cadia raise the defiled banner of the Chaos Eight-Pointed Star. Suddenly, an endless wall of fire erupted from the Volscani ranks, and heavy armor units began to grind over the bodies of the unsuspecting Cadian soldiers.
It was a shameful betrayal. Millions of Volscani had turned to Chaos. In what should have been the safest rear-echelon area, few were able to react in time. It was a massacre. Countless unprepared Cadian soldiers were butchered by their former allies, and nearly the entire High Command was wiped out in the initial volley.
Simultaneously, a massive Chaos fleet was detected in Cadian orbit. At its heart was the nightmare of every Imperial citizen: the Vengeful Spirit, the former flagship of the Arch-Traitor Horus.
The Imperial Navy near Cadia immediately engaged the threat. All available Imperial ships began to converge, and both sides locked into a fierce orbital battle.
"So the Black Crusade of the Despoiler has truly begun?!" A middle-aged man wearing a standard-issue Cadian uniform and a weathered overcoat paced the room. A diagonal scar cut across his forehead and down to his cheek, giving him a fierce, indomitable appearance.
"Yes, Ursarkar. The entire High Command has perished. Governor Primus Baulys has been assassinated. Now, only you can shoulder this burden..." Commissar Jarran Kell looked at the anxious Ursarkar E. Creed. "You have been urgently promoted to Lord Castellan, though it has not yet been ratified by the Senatorum Imperialis..."
"Bang!" Creed walked to the reinforced armored viewport and slammed his fist against it. "Then let them ratify it after the battle!"
He whirled toward the door and barked his orders. "Someone, relay my commands! Deploy every available unit to Tyrok Fields immediately to suppress the rebellion! Send messengers to inform all Astartes Chapters of this shameless betrayal!"
Over the course of those grueling days, millions of elite Volscani Cataphracts, supported by heavy armor and tides of mutants and cultists pouring from dropships, assaulted the Cadian positions. They had occupied the entirety of the Tyrok Fields and had begun to lay siege to the surrounding fortresses.
The tide of the battle shifted only when the elite Kasrkin assault regiments entered the fray. They joined forces with the Black Templars and a massive contingent of heavy armor to launch a counter-attack.
"Traitors!" Marshal Amalrich of the Black Templars shouted, his Black Sword cleaving through the heretics before him, the sheer force of the blow tearing their bodies asunder.
Amalrich surveyed the sprawling battlefield and charged into the enemy lines at a speed nearly invisible to the human eye. Foul blood sprayed as the corpses of traitors were ripped apart like rags. Several las-beams struck his armor, but they were harmlessly dissipated by his refractor field. A simple shoulder-charge from the Space Marine was enough to turn the traitor who had ambushed him into a red smear of meat.
After hours of relentless slaughter, he stood atop a mountain of corpses. He pointed his longsword toward a distant, hovering heavy dropship, the blood on his blade sizzling as it evaporated in the heat of the power field.
"Bring it down!" Amalrich roared. "None of these cowards shall escape justice!" The cross of the Black Templars branded upon his forehead pulsed with his righteous fury.
Following the Marshal's command, a volley of missiles struck the dropship in mid-air. After several white trails crossed the sky, a violent explosion engulfed the vessel. The massive ship disintegrated, its flaming debris raining down upon the earth.
Across the battlefield, the traitors were methodically purged by the fearless Cadian soldiers. As the banners of victory were raised one by one, Creed arrived at the front lines. Looking out over the field littered with craters and the dead, he spoke solemnly. "We have paid a terrible price for a single act of misplaced trust."
"The Chaos fleet in orbit has retreated toward the Eye of Terror. We have secured the surface," Commissar Kell said in a low voice. "Admiral Quarren has led his fleet to pursue the remnants. They suspect the Despoiler is aboard the Vengeful Spirit."
"No, I have a feeling this is far from over." Creed lit a cigar and placed it between his teeth. "Recall Admiral Quarren. And notify the commander of the Kasrkin 12th Regiment. Have them report to me. I have a mission for them."
"Have the adjutant tally our losses, then send him to my quarters," Creed said before turning to leave.
"What shall we do with the bodies of these traitors?" Kell asked.
"Burn them."
"But the fuel consumption..."
"I said burn them. Cadia will not yield a single inch of its soil, not even the earth used to bury traitors." Creed's voice faded as he walked into the distance.
"Understood," Kell replied, watching the broad, defiant back of the new Lord Castellan.