13th Black Crusade - The Storm Breaks: With the worlds of the Cadian Gate all but on their knees with the weight of internal strife and the outbreak of the so-called Plague of Unbelief, Abaddon the Despoiler launched an invasion into the Emperor's realm and unleashed a power beyond imagining, the scale of which had not been seen since the darkest days of the Horus Heresy.As part of their constant vigil around the Eye of Terror, highly trained units of Cadian Kasrkin often pushed into the outer reaches of that swirling maelstrom, desperate to find some indication of where the first blow would land in early 999.M41. Astropathic divination pointed towards the blighted world of Urthwart, a world already taken by Chaos, its population enslaved and sacrificed to the Dark Gods. Finding nothing alive on Urthwart, merely death and hideous Plague Zombies infected with the Curse of Unbelief, the Karskin prepared to withdraw. Suddenly, a frantic Vox communication from the Cadians' warships in orbit reported numerous vessels advancing on Urthwart from the Eye of Terror. The Karskin attempted to fall back to their dropships to return to their troop carriers, but it was already too late. The Imperial ships in orbit were either crippled or were forced to disengage and make best speed for Cadia.There was to be no escape for the Karskin who were stranded on Urthwart as a massive vessel, larger than the most gargantuan capital ship of the Imperium, approached the doomed world: the Planet Killer. Few were aware of the existence of this monstrous ship, for it had been thought lost at the Battle of Kharlos II during the Gothic War centuries earlier. Oblivious to their fate, the stranded Cadians could do nothing as the incomprehensible power of the Planet Killer was unleashed in a devastating lance of energy that annihilated the blighted world they were trapped upon and reduced it to spinning pieces of molten rock floating in the void. As Urthwart died, collapsing in on itself, a Chaos warfleet composed of hundreds of warships and hulking troop transports surged from the depths of the Eye of Terror, heralding the beginning of Abaddon the Despoiler's fearful 13th Black Crusade. A psychic death scream, more piercing than the Astronomican itself, ripped through the ether from the doomed world of Urthwart.Astropaths and forward Imperial listening posts detected the emergence into realspace of a Traitor warfleet consisting of hundreds of warships and hulking troop transport vessels. All were on a course for Cadia. Reports indicated that the Plagueclaw and Terminus Est, along with a massive flotilla of Plague Hulks, had emerged in the Subiaco Diablo System. Worse than this, unconfirmed reports claimed that two Blackstone Fortresses accompanied the Chaos warfleet. Cadian Sector High Command found this last fact difficult to countenance, though given the state of the sector in the previous solar months, they could not discount the possibility that these ancient xenos weapons still existed within the hands of the Forces of Chaos.Imperial naval experts began plotting worlds likely to be chosen as targets for the Planet Killer's attentions. Intelligence gathered during the Gothic War indicated that the Planet Killer was a ponderous vessel, and its planet-cracking Armageddon Gun took a great deal of time to power up and exert its effect upon a world once it was functional. The vessel was likely to be accompanied by a large fleet, which would be employed to subdue and distract the Imperium's own naval forces until the Planet Killer could unleash its main weapon. All available Imperial naval assets had therefore been tasked with locating such a flotilla, and system defence pickets were put on high alert for any signs of an unusually large Chaos warfleet approaching one of their worlds.