War of Beasts
Not to be confused with the War of the Beast that took place in M32
The War of Beasts (aka Armageddon on steroids, later the War of Nightmares) is the term used to label the ongoing conflict between the forces of the Imperium of Mankind and the various Xenos and Chaos forces trying to wrest its control of the strategic planet of Vigilus. The loss of Vigilus would mean the loss of a vital staging area for the Imperium for any kind of crusade into the Dark Imperium, and as such it is important for it to stay in Imperial hands.
- 1 The Opening Phases
- 2 The Conflict Escalates even MORE
- 3 Bad Portents, Bad People
- 4 All Downhill From Here
- 5 The Aftermath
The Opening Phases
The Speed Freekz Cometh
The first major threat to hit the planet in the wake of the Great Rift opening was a massive Waaagh! of Orks. Bursting from the Rift seemingly at random, and led by powerful Speed Freeks, the Ork fleet easily broke through the naval cordon and landed its boyz in the deserts between the great hives.
While most of the fleet crashed and burned, the Orks soon used remains of the downed fleet to create ramshackle scrap-cities, and from there Speedboss Krooldakka roared out at the head of a massive force of bikes, trukks, and battlewagons. Still reeling from the birth of the Rift, the Imperial forces gathered could do nothing to stop it.
At first, the Orks met little success, as the force fields were too strong. Growing bored, they resorted to raiding caravans or battling and racing each other in the massive deserts outside of the hives. This state of affairs didn't last however; the Great Rift continued to grow, and with its expansion Warp Storms washed over Vigilus.
The bastion fields soon flickered, then failed outright, which was what the Orks were waiting for. The green tide rushed to each Hive, and despite the best efforts of the Imperial Guard, the Skitarii of the Adeptus Mechanicus, and the Sisters of Battle, it was all they could do to avoid being overwhelmed.
They Came From Underneath
Despite the threat of the Orks, there were threats to the defense of Vigilus much closer to home. Centuries before, a Genestealer Cult derived from the Pauper Princes had managed to get a single Purestrain Genestealer onto the world. The Genestealer grew into the Genestealer Patriarch called the Grandsire Wurm, and its cult refused to let its years of preparation go to waste due to the unexpected greenskin arrivals. Uprisings that were supposed to be triggered decades down the road were forced to do so prematurely, and soon every Hivesprawl was in chaos due to the simultaneous insurrections. Imperial defenders fell to synchronized ambushes across the planet, as the Cult consolidated its hold on the Hives.
The response to the Genestealer Cult-led revolt was slow, as the Imperial Government initially thought it was the work of criminals and malcontents, and instead focused on shoring up its defenses. These uprisings, plus the constant ork raids, essentially forced the industry on the planet to grind to a halt. Things were, to put it mildly, looking grim.
Tooth and Claw
It was at this point that a task force of Space Marines made of elements from the Iron Hands and the Brazen Claws, decided to throw their hats into the proceedings. On the way to the Stygies Front, they made a detour to Vigilus once contacted by their Mechanicus allies. Led by Kardan Stronos, the Astartes made a massed drop pod assault on the outskirts of each major Hivesprawl, before converging toward Megaborealis. Expecting to find Orks, they found cultists and Genestealers instead. Battles with these cultists would keep the sons of Ferrus Manus busy for many months.
Later on, a second task force of Astartes, this time Space Wolves from the Great Company of Ragnar Blackmane arrived to do battle with the xenos occupying the Oteck Hivesprawl. There was little coordination between the Wolves and the Iron Hands, and hilariously none of these Chapters saw fit to inform the Vigilus ruling council of what the heck was going on in their cities.
The Megaborealis Throwdown
A Mechanicus stronghold, it was thought unassailable by Ipluvius XIV, the Magus Dominus in command of the Skitarii forces there, enough that he let himself get distracted by his studies. However, a squad of Ork Kommandos begged to disagree, and brought down the hive's forcefield. The massive speed freekz attack that followed, coupled with a simultaneous attack by genestealer cultists, caused the magos' cogitators to freeze up due to the stress, leaving the defenders without coordination. It was bad enough that the cultists were able to steal Vortex Missiles and detonate it in the middle of the Hivesprawl, destroying countless Imperial war assets (including the Warlord Titan Dominus Rex).
In a decisive move, Archmagos Nesium Caldrike took control of the remaining defenders, and coordinating with elements of the Iron Hands Clan Kaargul put a stop to the Genestealer shenanigans, for now at least.
While all of this was happening, the Imperial Guard was making a large-scale counterattack, with the aim of reinforcing Megaborealis. The armored convoys of Leman Russes and Chimeras took a heavy toll on the greenskins, but all this just seemed to draw more and more mobs of speed freekz to the convoys.
Chaos Crashes The Party (Literally)
At Hivesprawl Dontoria, already under pressure from mysterious attackers (who turned out to be Dark Eldar opportunists), an unknown spacecraft decided to crash into the hive's center, despite the best efforts from the anti-air emplacements surrounding it. From its ruined depths came the mutants of the Gellerpox Infected, but the worse was to come, as in their wake came the Heretic Astartes of the Death Guard.
While the Tempestus Scions there were able to repel the Infected's assault, the sons of Mortarion soon overwhelmed the defenses. In desperation the Hive's lower levels were firebombed in a two-mile radius, but this was not enough to contain Nurgle's followers, and soon the Gellerpox spread through Dontoria. Despite the warnings of Rogue Trader Delarique du Languille, the Aquilarian Council was slow to react to the threat. Acting on a warning from her psyker servant that the Gellerpox would threaten Terra if left unchecked, she took matters into her own hands. The Rogue Trader was able to halt shipping offworld and intercept and destroy what was thought to be the only Gellerpox-infected vessel departing Vigilus- but it was later found that two other infected ships had escaped and were now headed directly to Terra.
Here Come Guilliman's Boys
After receiving a vision from Tigurius, as well as a message from Roboute Guilliman to not allow Vigilus to fall, Chapter Master Marneus Calgar rushed as many of the Ultramarines that he could spare to the planet's defense. The going was difficult, and even with Tigurius' guidance many Epistolaries die to get the Chapter to the world on time.
Once there, he swiftly had those in the Aquilarian Council he determined to be Genestealer Cult infiltrators executed, and had the Vigilus Senate set up in its place.
Wolf Bites Bug
The Space Wolves of course, were not idle. At Oteck Hivesprawl they tried to reclaim the all-important water supply back from the cultists. Things turned nasty very quickly when the Wolves' artillery support in the Imperial Guard turned out to have been controlled by the Cultists, and a whole lot of Hive City was suddenly dropped on the Wolves' heads. Many died, but enough Battle Brothers remained to continue the hunt for the xenos. The cultists were finally cornered and annihilated, but in their wake they left the water supply mostly tainted.
Haldor Icepelt, the commander of the Space Wolves there, ordered whatever explosives the cultists stockpiled found, and then used these to bury the polluted water source under tons of rubble, preventing its spread to other hives.
The Conflict Escalates even MORE
Wake the Dead
It was at this point that one Farseer Keltoc from Craftworld Saim-Hann had a vision suggesting that it was important for its forces to intervene in the conflict, as something there would influence the future of the Eldar race. Apparently a home-grown Tzeentchian cult led by one Vannadan planned to trigger a magma explosion that would eventually wipe out the leaders of Vigilus' defense, which would lead to the loss of the planet to Chaos, so they can't have that now, can they? Amazingly, one of the times the Eldar had genuinely good intentions (for themselves like usual, but in a way that honestly benefits someone else).
Using an underground Webway gate to avoid their dark kin, the Saim-Hann task force, led by Autarch Rhyloor and Spiritseer Quelanaris, swiftly isolated the Chaos cultists and slaughtered them to a man. Word of their arrival spread to the Imperial Guard stormtroopers stationed nearby however, and the Imperials rushed to the location, fully convinced that these were the same Eldar who had been gleefully raiding the Hivesprawls during the past few months (and the Imperium does not distinguish between types of Eldar because all xenos are equally deserving of annihilation).
Quelanaris and Rhyloor tried desperately to explain to the arriving Stormtroopers that, no, they looked nothing like the Dark Eldar dicks who were the cause of all the trouble and that they had just eliminated a major threat to the planet (keep in mind the Imperials had no idea that the humans they had just killed were Chaos Cultists or indeed even knew there was a Chaos cult in the planet). The Tempestor Prime in charge, however, did not know or care about the difference between the Craftworlders and Dark Eldar let alone believe their story, and so the Imperials opened fire.
Many Eldar were cut down, including Rhyloor, but Quelanaris managed to escape with his fallen comrades' spirit stones. Vowing vengeance, he had the spirit stones installed into waiting Wraith Constructs and led a second strike Force back to Vigilus to avenge the Autarch.
Some time later, this strike force attempted a direct attack on the Imperial leadership council as revenge for their recent losses. Primaris Lieutenant Eothrus of the Ultramarines attempted to talk down the Spiritseer, having heard about Saim-Hann assisting the Space Wolves on Stygius from Haldor Ice-Pelt, but Quelanaris refused to listen to reason and ordered his forces to attack.
The Carnival of Pain
While the Imperial Guard wasted their time with the Craftworlders, the actual Dark Eldar continued their merry time harassing and generally making the residents of Hivesprawls Hyperia and Oteck wish for the swift release of death. Led primarily by the Haemonculi coven of The Altered, Kabalite troops joined with Wych cults and Haemonculi constructs in raids that were both spectacular and deadly. The Altered in particular had a specific beef with the Ultramarines, as Guilliman had kicked their ass in during the Indomitus Crusade, and took particular amusement in hauling entire squads of Ultramarines back to Commorragh for "entertainment".
Holding Back The Foul Tide
Back in Dontoria Hive, the newly-arrived Primaris Chapter Necropolis Hawks fought to hold back the Gellerpox Infected, while the Crimson Fists and the Iron Hands worked to create a barrier with the assistance of du Languille to hold back the Chaos-spawned plague. Using the PDF's hellhound tanks, the Fists set fire to the hive's promethium pipelines, creating a literal firewall around the infected zone.
The Mortwald Defense
With the destruction of the waterworks at Oteck Hivesprawl, water was getting harder to come by at Vigilus. Dontoria's own water source was also in danger of contamination, due to everyone forgetting that the Death Guard had already made landfall.
Mortwald, the source of most of the planet's food and medicine, was also under threat. Defending it were regiments of Ventrillian Nobles, Vostroyan Firstborn, and Cadian Shock Troopers, all under the command of Deinos, the surprisingly-competent brother of the Imperial governor.
When the Greenskins came, the trench network Deinos had prepared showed its worth, and slowed down the advance of the Orks for Weeks. Within the walls of the Hivesprawl, the Guard proved themselves equally adept at putting down Genestealer Cult uprisings. Lord Deinos was adamant -- Mortwald will not fall -- and his mantra became the rallying cry of the defenders there. This stalwart defense was only improved by the arrival of the Imperial Fists 5th Company under Brother-Captain Dravatis Fane, though his forces would be tested as Ork Stompas emerged by the hundreds. Although his forces had to retreat to higher ground, Fane would counter-attack. With him were loyalists Knights from House Terryn, as well as Freeblades formerly from the traitorous House Mandrakor.
In a charge that was the stuff of legends, the knights attacked the Stompa horde. Supported by the Reaver Titan Heresium's Bane, the Knights actually forced the Orks to break. Rather than running them down, the Imperials halted (notwithstanding the Freeblades who wanted to pursue them), as they insisted that the defending the people of Mortwald came first. This decision would soon bite them in the arse however, as a few days later the Orks attacked. While it was driven off easily enough, these attacks increased in strength week after work, until the Imperials were facing machines the size of reavers.
Fane had enough. He ordered an expedition into the wastelands to find the factories churning these machines out, and put them out of commission. Permanently.
The Imperial forces found a large scrap city east of Mortwald and, under the cover of a dust storm, attacked. With Warhounds as support, the Knights identified, then destroyed the major factories. With the mission completed, Fane ordered a withdrawal, but the Freeblades in their zeal to redeem themselves ignored this, and charged straight into the next scrap city. Much facepalming ensued, as while the Knights killed countless orks in their reckless attack, they soon found themselves surrounded.
Fane led an airborne rescue force alongside elements of the White Scars Brotherhood led by Olujin Khan and Dark Angels Ravenwing commanded by Meneraeus to aid the beleaguered Knights. The Stormtalons of the White Scars destroyed the anti-air and artillery emplacements, and without these the Bike Squads of the two Chapters cut a path through the Orks.
Without warning, the Ravenwing suddenly abandoned the attack, and thundered into the dusty wilderness of the Vhulian Swirl. The White Scars, now bereft of support, found themselves on the verge of being swamped by Greenskins, so Olujin was forced to call a fighting withdrawal.
Back at Megaborealis the Mechanicus and Iron Hands was getting their Genestealer problem somewhat under control. The Sons of Manus would lead the attacks, then the Mechanicus would handle clean-up. Using xenos-detection tech, the Genestealer nests were found and destroyed, which forced the Pauper Princes to slink back into the shadows and resort to guerilla warfare to strike back.
The same could not be said of the Stygian Spires region, which controlled the asteroid water mining operations of Megaborealis. Led by the Grandsire Wurm itself, the Cultists overwhelmed the Skitarii defenders. Before long, the top levels of the water plant were taken over by the Patriarch and its kin.
Bad Portents, Bad People
Despite all of this, the general consensus of the population was that things had stabilized enough that the Imperium just might eke a win out of all this. This, despite Calgar being forced to have Dirkden's civilian population evacuated.
Then things really started to go tits up. Reports of disappearances and horrible monsters in the upper spires started to spread, with everyone trying to investigate vanishing without a trace. The Great Rift seemed to darken in the sky, and readings of the Emperor's Tarot all produced the same ominous reading.
By the time the Ordo Malleus had deciphered the mumbling of comatose Imperial Psykers as a warning about a "Dark King", the monsters had been identified as a scouting force of Black Legion Raptors, Heldrakes, and Warp Talons.
Soon afterward, every vox network on the planet received a message from Haarken Worldclaimer, the Chaos Raptor Lord leading the Black Legion forces and Herald of the Apocalypse: Vigilus now belonged to Abaddon and the Despoiler would soon arrive to oversee its conquest personally.
As the Vigilus Senate convened to discuss the alarming turn of events, they were attacked by a Heldrake that smashed through the Senate spire's ceiling. The Victrix Guard were able to prevent it from harming Calgar, but now they had to deal with the impending arrival of the Warmaster himself.
Meanwhile, Thousand Sons Rubric Marines were burning their way through Oteck Hivesprawl, a new Gellerpox outbreak in Mortwald led the nobles to hoard food and water for themselves and inadvertently inspire even more Chaos and Genestealer Cult uprisings, and the defenses of the planet were being stretched thinner and thinner. And the bulk of the Black Legion's forces hadn't even shown up yet.
Haarken had boasted that Vigilus would fall within 80 days of his arrival. Sure enough, after 80 days a massive number of Warp signatures was detected in the Nachmund Gauntlet.
The War of Nightmares had begun.
Shadowspear At Nemendghast
During all of this madness, at the outskirts of the Vigilus System a taskforce of Vanguard Primaris are covertly inserted into the planet Nemendghast after receiving a distress call from there. To their horror, they find that the world had already been taken over the Dark Powers, and its forges used to churn out Daemon Engines for the Black Legion. As it turns out, it had been trapped within the Great Rift for a time and Abaddon had taken the opportunity to capture it as a staging area for his planned invasion force.
Although heavily outnumbered by the Daemonkin there, the task force, led by Ultramarines Librarian Maltis, try to sabotage the forges ruled over by Master of Possession Vorash Soulflayer. It succeeded, but at great cost, with only Maltis escaping to bring word to Calgar of the Black Legion fleet's imminent arrival.
Clash in the Void
Having learned of the approaching fleet from Maltis, Calgar called for a double cordon to intercept the Chaos armada. In spite of a torpedo barrage meant to box in the fleet, the Imperials were pushed back after the Chaos forces began summoning daemons onto the Imperial ships. Even Calgar's own flagship Laurels of Victory was not spared, and he was wounded by the Keeper of Secrets that manifested onboard.
Following his return, Calgar had no choice but to abandon Dirkden Hivesprawl and Kaelac's Bane in favor of shoring up the defenses of Mortwald, Megaborealis, Oteck, and Dontoria.
While Vannadan's plan had been thwarted by the Eldar intervention, the pyroclastic cults of Storvhal soon rallied around Haarken Worldclaimer. After defeating the local Skitarii defenders, they were able to open a Warp portal to summon an army of daemons of Tzeentch; soon even the volcanoes were erupting with warpfire.
The quick thinking of Fabricator Vosch was able to stop the continent from being swallowed by Chaos by using Tectonic Fragdrills to trigger a massive but more conventional eruption that wiped out both Chaos forces and whatever AdMech couldn't get out of the way. Even then, Storvhal remained in Chaos hands, with Worldclaimer's Raptor packs using the ash to conceal their movements.
Around this time, another detachment of Space Wolves led by Krom Dragongaze arrived to reinforce Vigilus. Showing his well-known disregard for little things like "waiting for orders", he immediately led an assault on the Ork-held Space Hulk Worldsmasha. Following the destruction of several smaller hulks by the Wolves' Battle-Barges, Krom's forces were able to teleport directly to the Worldsmasha and kill its Big Mek commander before sending the Space Hulk on a crash course with an Ork settlement.
Marneus Calgar was less than impressed with Krom's recklessness, but news of a renewed greenskin threat in Hyperia prevented them from coming to blows over the matter.
The arrival of Abaddon's fleet had demoralized the population even further. Looting and rioting were widespread, and many of the despairing populace had turned to the Genestealer Cults or Chaos if they had not simply become Zealots for the Imperial Cult.
However, Abaddon had underestimated the strength of the xenos on Vigilus. Initial attempts at capturing the spires were stymied by Orks and the Pauper Princes, forcing Haarken to change his initial plans. An attack on Dirkden by the Night Lords and The Scourged killed millions of the cultists, but ultimately failed under a massive assault by Metamorphs and Aberrants.
Sisters of Battle: Not Jobbing This Time
The Genestealer Cultists had also started to tunnel underneath Dirkden into Oteck in the hopes of spreading their uprising further, but the Sisters of Battle from the Order of the Argent Shroud and the Order of the Last Prioress were able to keep them contained. Exploration of the tunnels revealed that they had already begun infiltrating Hyperia, though, and the Sisters' plans to counter-attack through the tunnels had to be put on hold.
The Orders Dialogus had also kept busy by mapping the Ork Speedwaaagh! races, allowing Imperial convoys to be ready for the greenskins' raids. This frustrated the Orks enough to get them to go out of their way to hunt down convoys protected by the Sisters.
Retaking the Hoist
To deal with their water problem, the Imperials set out to recapture the Omnissian Hoist from the Genestealers. The cults had already been weakened by a prior skirmish with the Magma Hounds warband, allowing a combined force of Iron Hands and Skitarii to push through the alien hordes.
The Grandsire Wurm itself was forced to lead the counter-attack, eventually sealing itself into the hoist's main control center in a final effort to deny it to the AdMech. But it hadn't counted on the Onager Dunecrawlers that had crawled up the structure, and it was forced to retreat after being wounded. After that, the Dunecrawlers were able to mop up the remaining Purestrains without difficulty.
Hyperia Hivesprawl had at this point come under heavy attack by the Iron Warriors and the Word Bearers, the latter of which had taken the time to build Noctilith Crowns to summon even more daemons. After receiving news that the Black Legion had led a major assault into a critical water purification plant on top of another Gellerpox outbreak, Calgar had no choice but to take desperate measures.
On the advice of the Planetary Governor, massive fires were started in each of the major Hivesprawls to prevent their corruption from spreading further. "Calgar's Fires" did manage to eliminate considerable parts of the xenos and Chaos forces, but only at a terrible cost. Even worse, the Vengeful Spirit had arrived on Vigilus and was effortlessly destroying every Imperial vessel sent to repel it.
The Fallen Angels are Assholes
Abaddon's first course of action was to pay a visit to the center of the Vhulian Swirl. The great storms were in fact artificial, and intended to conceal the location of a fortress called the Citadel Vigilant that had been occupied by a group of Fallen Angels that had forged a blood pact with Abaddon during the Pandorax campaign. Their leader, the former Librarian Osandus, had come into possession of a gravitic weapon dating from the Dark Age of Technology, dubbed the Voidclaw.
Osandus had originally planned to lure the Dark Angels to Vigilus using hints from Fallen that let themselves be captured as bait; they would bring the Rock with them, and the Voidclaw would then be used to destroy it and wipe out the Dark Angels in the process. Abaddon sought to use it on the space between Vigilus and its moon Neo-Vellum, altering the planet's orbit in a way that would reshape the Nachmund Gauntlet if not close it completely, thus ensuring that the Imperium Nihilus was lost for good.
The Fallen Librarian was pleased to help with such a major blow against the Imperium, and the Voidclaw was fired. Needless to say, this royally fucked over just about everybody on Vigilus. Mercifully, the Dark Angels were later able to find the Citadel Vigilant, destroy the Voidclaw before it could close the Gauntlet, and deal with the Fallen in their usual manner.
All Downhill From Here
As you would probably expect, the Imperials were left badly reeling from the Voidclaw's activation. Calgar managed to salvage things somewhat by manipulating Chaos forces into clashes with the Speedwaaagh!, but even then the Imperials were struggling and countless hives had been badly damaged if not outright destroyed.
At Mortwald, the Imperial Fists and Iron Warriors had been engaged in a long trench war, but when they and Deinos' elite forces were forced to redeploy against other threats the Hivesprawl fell to the forces of Chaos. The nobles that had been hoarding food all this time unsurprisingly fell to Slaanesh, a situation that the Flawless Host used to their advantage by overwhelming the defenders with Daemonettes as they shut down the automated defenses. By the time the Imperial Fists could respond, the rioters opposing the corrupt nobles had devolved into cultists of Khorne.
At the peak of the Death Guard invasion of Dontoria Hivesprawl, the Gellerpox-infected freighters that had departed near the beginning of the war came back, now full of mutants eager to claim Dontoria for Nurgle.
The Purge were insulted by the Death Guard's sudden influx of corrupted life, and sought to deal with it in their traditional manner: with lots of chemical weaponry. Citizens and mutants alike were thrown into manufactorums, producing a foul miasma that suffocated everything it came into contact with. As you might expect, the Death Guard and the Gellerpox Infected did not appreciate the interference and the two Nurglite armies quickly turned on each other.
Marneus Calgar decided that breaking their stalemate would not be worth it; even if the Nurglites could be driven off, Dontoria was now a hopelessly corrupted shithole too far gone to be saved.
The Dark Eldar and the Thousand Sons spent most of the later parts of the war fighting over the Webway Gate at Kaelac's Bane. The Dark Eldar seemingly triumphed after unleashing stolen terraforming devices that froze the Rubric Marines solid, but before retreating to the Webway their sorcerers left them a "parting gift": a Keeper of Secrets. This particular Keeper of Secrets, known as "The Pale Stalker", was able to blend in perfectly with the blizzards, and within three weeks it had slain nearly a third of the Dark Eldar forces. The survivors were left so petrified of the daemon that they abandoned Vigilus outright. After one last slave raid, of course.
Like Primarch, Like Chapter Master
The Imperial forces were increasingly confronted with the possibility that they were going to lose. Chaos kept gaining ground, and the remaining relay stations on Neo-Vellum were warning that the Great Rift was expanding closer to Vigilus. Left unchecked, the world would be lost to the Warp and the entirety of the Imperium Nihilus with it.
Some among the Vigilus Senate brought up the prospect of Exterminatus, but Marneus Calgar reminded them that Guilliman told them not to abandon the planet under any circumstances. More importantly, the Chaos forces were still being weakened by the xenos and Imperial forces were still eking out victories here and there.
While seeking the aid of the Orks was out of the question, Calgar decided that an alliance with the Eldar of Saim-Hann would work to their mutual advantage. During a lull in the fighting, Calgar was able to call for a parley and meet with Farseer Keltoc. While Keltoc was still upset with the death of Autarch Rhyloor, the Farseer agreed that the Eldar could not afford for Vigilus to fall.
The exact details of the pact Calgar made with Keltoc are uncertain, but given that the Farseer and his senior chieftains were allowed into the Governor's Palace and that the Planetary Governor and the other members of the former Aquilarian Council who had a role in Rhyloor's death were never heard from again, it isn't difficult to figure out the terms. In exchange, the Eldar agreed to allow the Imperials the use of the stealth ship Vaul's Ghost, which Calgar needed to carry out his plan to force the Black Legion's withdrawal.
The Eldar soon began to create a diversion for the Imperials, leading Orks into Chaos Space Marines strongpoints across Vigilus. While countless battles continued to rage, only Calgar, Keltoc, and a handful of Ultramarines commanders knew that only one- the battle for New Vitae Docks- mattered. Countless bulk freighters were sent into low orbit despite the Iron Warriors' best efforts to shoot them down. Most were decoys, but one of them was carrying a payload of six Deathstrike Missiles- including two Vortex Missiles. Meanwhile, the Imperial fleet had been hastily reassembled to engage the Black Legion's fleet, in the hopes that it would buy enough time for the Vaul's Ghost to pick up the missiles.
The Main Event
To ensure that the Warmaster couldn't catch onto what the Imperial fleet was planning, Marneus Calgar challenged Abaddon to a duel at Saint's Haven. The Despoiler was eager to humiliate the Chapter Master, and promptly teleported there with a retinue of Terminators and Possessed.
As their bodyguards fought, Calgar and Abaddon exchanged volleys of bolter fire before a loose flagstone left the Chapter Master off-balance long enough for the Warmaster to damage one of the Gauntlets of Ultramar. Calgar countered with a punch strong enough to knock Abaddon off his feet, but a slash from Drach'nyen cut off two of Calgar's fingers, badly damaged his armor, and destroyed his secondary heart.
As Abaddon prepared to finish off Calgar, he received an urgent warning from Worldclaimer: the Vaul's Ghost had crashed into the Vengeful Spirit, detonating the Deathstrike Missiles in its hold and blowing a massive hole in the Black Legion's flagship. The critically damaged battleship would soon make an emergency Warp jump out of the Vigilus system, and Abaddon would have no choice but to teleport back to attend to the ship.
The Despoiler chose to leave his Possessed retinue behind to make sure Calgar didn't have the chance to learn his plan worked, but his Belisarian Furnace kicked in just in time to help him fight them off. By the time the Victrix Guard arrived, Calgar was on death's door (again) but was saved by his Apothecaries. However, he hasn't taken the field personally since then and is likely still recovering.
The war didn't immediately end with Abaddon's departure, but without him to hold them together the forces of Chaos have splintered and begun fighting among themselves. The Despoiler has not allowed his setback to stop his plans to close the Gauntlet, though. In fact, he has already planned an attack on Vigilus' sister world of Sangua Terra, to be spearheaded by the Planet Killer itself.
Megaborealis was retaken by the combined forces of the AdMech and the Iron Hands, and while the Black Legion was able to destroy much of the Blackstone deposits that kept the Nachmund Gauntlet open with a cyclonic torpedo bombardment the cogboys kept enough of the stuff hidden away for the Gauntlet to stay stable. Hyperia is still contested, but Oteck and Dirkden are considered lost.
Speedboss Krooldakka was slain during the Black Legion's bombardment of Megaborealis, and while the Orks are a spent force in Vigilus' cities they still hold a considerable amount of territory in the wastelands. Two-thirds of their scrap cities are estimated to be intact, and word of Vigilus being a fun fight has attracted Orks to the world, just like on Armageddon.
With the Black Legion repelled and their honor avenged, the Eldar of Saim-Hann left without much fanfare from anyone.
The Pauper Princes still infest the entirety of Dirkden Hivesprawl, but their plans have suffered a blow that they may not be able to recover from. They now look to the stars for salvation, hoping their Star Saviors come to their aid. Grandsire Wurm was slain by a trio of Callidus Assassins disguised as Neophyte Hybrids, but the cult had spread far enough for multiple Patriarchs to arise, with one of them becoming the new Grandsire Wurm.
Vigilus itself is about as badly fucked over as you would think, but with the threats to Vigilus now being at relatively manageable levels the Imperium can now consider the planet to be safely in their hands. For now, anyway.