Vigilus

Vigilus is an Imperial Hive World located in Segmentum Obscurus. It is now the focal point of a massive free-for-all as the Imperial Forces there try to keep the planet from the hands of Orks, Eldar and Dark Eldar invaders from without, an insidious Genestealer Cult trying to subvert the planetary defenses from within, with finally Chaos madmen in the form of the Gellerpox Infected joining the fun.

And then the Herald of Abaddon the Despoiler decides to come a-knocking...

About the Planet Itself

Prior to the opening of the Great Rift, Vigilus' main claim to fame (and indeed its main planetary export) was force field technology, specifically bastion-class fields, which were powerful enough to protect entire hive cities. Its own cities are enveloped by these fields, increasing the world's defensive capabilities.

Both the Adeptus Mechanicus and the Ecclesiarchy have a significant presence on the planet, the former due to an ancient treaty signed with the ancestors of the current ruling dynasty, and the latter heavily influencing the local PDF (named the Vigilant) as well as the Imperial Guard garrison. Not surprisingly, there are a lot of Sisters of Battle around to enforce the Ecclesiarchy's will.

Not surprisingly, the nobility, the Mechanicum, and the Ecclesiarchy don't get along too well, but have stopped short of outright civil war thanks to the efforts of the Aquiliarian Council, which is made up of more reasonable members of the three factions. That, and because A) the Mechanicus would butcher anyone who endagers such a techy planet and B) any Imperial force that starts a war against the planetary government would be considered renegade and blown up from orbit. The Imperium does not tolerate Imperial forces playing warlord. It didn't exactly go well for the Imperium the last time that happened. Times, really. Hell, one of the things keeping the Ecclesiarchy crazies restrained is the knowledge that if they got violent everyone and their pet rock would be screaming "Reign of Blood!". Which would be very bad for them.

Then, The Great Rift Happens

With the Fall of Cadia, Vigilus finds itself stuck on the north side of the Great Rift, in the Dark Imperium. What's more, the world's strategic significance rises exponentially when everyone realizes that it's located at the end of one of two known stable routes across the rift: the Nachmund Gauntlet.

It's hives still protected by the psychic charged bastion fields, the world had become a staging area for any Imperial expedition daring to brave a foray into Imperium Nihilus (indeed, the survivors of the Stygies Front were using it as a rallying point), and the final safe harbor for refugees trying get out of it.

The War of the Beasts

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 Come From Underneath

Despite the threat of the Orks, there were threats to the defense of Vigilus much more closer to home. Centuries before, a Genestealer Cult called the Pauper Princes infiltrated the underbelly of many of the hives in Vigilus. Led by the Genestealer Patriarch called the Grandsire Wurm, it 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 contacts. 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 were doing 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 Death Guard 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 a strange plague spread through Dontoria.

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 rushes 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 has those in the Aquilarian Council he senses to be in-cahoots with the Genestealer Cults executed, and has 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 "allies" in 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.