It all began in the Corathi system, when a Chaos raiding party attacked a local Adeptus Astra Telepathica space station, Virago Telepathica, orbiting the agriworld Halon’s Retreat. The attack puzzled the local planetary commander, because Halon’s Retreat was home to one of the Imperial Navy Battlegroup Virago and the Chaos raiding party was immediately annihilated. The main planet in the Corathi system, Corathi itself, is a famous Ecclesiarchy world and is also well protected.
The reason for this suicide attack became apparent when a large Chaos fleet led by Abaddon appeared in orbit and destroyed the Imperial fleet. The imperial authorities could not send a distress signal because of the damaged relay stations. An appearing Space Marine fleet from the Blood Angels and Black Templars Chapters was badly mauled before they could disengage. The Chaos fleet lost only the strike force and a single cruiser due to a lucky hit from a Lunar class cruiser. It then proceeded to launch a planetary attack on Halon’s Retreat and board the Adeptus Astra orbital station. The attack was successful and a battalion of World Eater Traitor Marines, led by Lord Sharac Khzar, was deployed on the planet.