Corvin Severax - Cometh the Ravens: As the White Scars gathered at a hidden munitions cache, a long figure emerged from the darkness. It was Shadow Captain Kayvaan Shrike of the Raven Guard, and he delivered a message to the alerted White Scars from his Chapter Master, Corvin Severax. The White Scars were to return to the capital and prepare to retreat offworld.A powerful Imperial fleet, including the Raven Guard Battle Barge, Wings of Deliverance, stood ready to aid in the evacuation. Agrellan could no longer be held against the T'au. It was well indeed for the Imperium that Corvin Severax had such a shrewd tactical mind. Had he not acted so swiftly and decisively to organise a full-scale evacuation, the planet-wide T'au assault would have decimated the Imperium's fighting strength in the Lithesh Sector.When the T'au attack came, it was so sudden and brutally efficient that many hive cities fell within the first few hours of the mass assault. The defences of every hive city had been meticulously analysed by orbital scans and advanced reconnaissance teams. The weaknesses of each of these strongholds had been discovered, and the appropriate cadres deployed to ensure their total destruction. Shadowsun developed a different plan of attack for each hive city, ensuring that if any defensive strategy proved effective, it would not work against T'au forces elsewhere.At the forefront of each and every assault strode the new XV104 Riptides. Wherever these mighty battlesuits engaged the beleaguered Imperial defenders, they slaughtered them and shattered their bulwarks. Only the Imperial Knights seemed able to withstand them on the battlefield, and even then, five Knights were felled by Riptide Wings during the Battle for Agrellan Prime.The defenders of Agrellan Prime had been bolstered overnight by the newly arrived Raven Guard 6th Company and the Cadian 724th "Wardens" Imperial Guard regiment, under Colonel Jericho Voss. Corvin Severax himself directed the hive city's defences, determined to see them hold long enough for Shrike and the White Scars to fight their way back into the city for extraction.But just when it seemed that the Space Marines and Catachans would make it back to Agrellan Prime, Shadowsung sprang her trap. A simultaneous pincer assault comprising four Counterstrike Cadres and Shadowsun's own Firestrike Assault Cadre slammed into both flanks of the Imperial column.Despite a ferocious counterattack from the White Scars and Raven Guard against the first wave of T'au attackers that drove them back, the arrival of a Riptide Wing turned the tide back against the Imperials. Shadowsun darted between the desperate fire fights, picking off the Imperial transports with methodical efficiency. It was at that moment, just when all appeared lost, that Corvin Severax played his trump card.The explosive arrival of this new combatant was evidenced when a vast Reaper Chainsword burst from the chest of a Riptide, before tearing the battlesuit apart in a welter of sparks. The Knight Freeblade known as the Obsidian Knight had entered the fray. Acutely aware of the specialist skills of this fabled Knight, Severax had sought out the relentless T'au-killer and transported him to Agrellan.The violence that ensued proved the Chapter Master wise, for the Obsidian Knight slaughtered the T'au forces with terrible purpose. Inspired by this veritable engine of death, the embattled Space Marines redoubled their efforts and hurled the T'au back. At the last, the Knights of House Terryn were able to fight their way through to relieve the retreating Imperial host. Only when the first of the Imperial transports were launched did Patriarch Tybalt grudgingly lead his few remaining Knights back towards the awaiting Imperial drop ships. With that final act, the Imperium withdrew from Agrellan, leaving the planet in T'au hands.