The Beheading

In 546.M32, the internecine politics of the Imperium take a calamitous turn when the High Lords of Terra are all assassinated by the orders of Drakan Vangorich, the Grand Master of the Officio Assassinorum. A Space Marine retribution force is drawn from the Halo Brethren, Imperial Fists and Sable Swords Chapters to track to the Grand Master to an Assassinorum temple. The commander of the strike force is assassinated as soon as he makes planetfall, but the Brother Marines commence their attack nevertheless. Within the temple they are assailed by a hundred Eversor Assassins. A single Space Marine survives the onslaught to reach the Grand Master and deliver the Emperor's judgement with his Bolter. The Imperium swiftly descends into anarchy.