The atrocity began when Lord Severin Drask of the Crimson Slaughter, acting in concert with Abaddon the Despoiler in the 13th Black Crusade, moved into the Achyllan System. Drask intended to use an ancient Chaos construct known as the Temple of Shades to extinguish the System's star and create a Warp Rift that would extend the Eye of Terror to Terra itself.
The Crimson Slaughter's genocidal plans accelerated quickly, with raids occurring throughout Segmentum Obscurus to distract the Imperials from their true target. Exploiting the situation, Drask led a brutal attack on Achyllan Prime's few defenders, sweeping aside Cadian Regiments. It was thanks to the efforts of the Primaris Psyker Lunst Cataboldine, who ripped the plans from Drask's head before his own death, that the Imperium became aware of the Crimson Slaughter's plans.
When the news was delivered to the High Lords of Terra they decreed that an Execution Force of the Officio Assassinorum be organized to stop Drask. The Officio launched Operation Deathblow against Drask, consisting of the Vindicare Assassin Viktor Zhau, the Callidus Assassin Klara Rhasc, the Eversor Assassin Sylas Torq, the Culexus Assassin Noctus Kord, and the Vanus Assassin Kurei Adamta. The Assassins were successful in landing on Achyllan Prime, but had to fight waves of Daemons, Cultists, and Chaos Space Marines on their way to Drask and the Temple of Shades. In the ensuing fight, all of the Assassins save Adamta were killed, but Drask was slain and Tzeentch lost interest in his pawns plans. The Temple of Shades shattered and Achyllan devastated.
- 1: Assassinorum: Execution Force (Game) Rulebook pg.20-32
- 2: Assassinorum: Execution Force (Novel) Chapter 4