Arguably the most important part of the Coup against Larion Ursus. The Battle of the Sector Palace was the armed conflict for control of the palace and the Sector Governor within.
After other factions such as the Adeptus Arbites and Order of Bloody Tears established perimeters and worked on stymying any response efforts, the primary task of invading the Palace itself fell to the Ghosts of Retribution.
Prior to the main assault, the revenants of the Ghost Company infiltrated the palace along with the blank Xenya. Whilst avoiding patrols and guards they successfully positioned themselves to apprehend Sector Governor Larion Ursus and eliminate as many witches and anti-air defences as possible once the assault commenced.
The main assault was led by Captain Brethorius and his Veterans of the First Company, closely supported by Captain Kay's Seventh Company. Soaring down upon the palace in a mixture of Thunderhawk Gunships and Drop Pods the astartes quickly took control of the outer palace, while Xenya helped nullify the powers of many witches allowing them to be dispatched with ease.
Once the outer palace was claimed, the battle for the inner palace focused around the main gate into the more heavily armoured bastion. This was the location of the fiercest fighting and where the vast majority of casualties on both sides was incurred. Amongst the defenders were the renegade astartes of Larion Ursus' Honour Guard, and they fought fiercely thanks to the enthrallment they haad been put under by the witches of Deidara Ursus' coven.
At one point in the battle Captain Kay was struck by a lascannon but emerged miraculously unscathed, before helping Captain Brethorius lead a final push that collapsed the defensive lines and struck the death blow against the palace forces.
Meanwhile the remnants of the Ghost Company attacked Larion Ursus' personal office where he was attempting to organise an escape for himself and his family. With the Sector Governor were Brothers Hadran and Ormius of the Honour Guard, and Hadran managed to kill Revenant Jaykor before the two Honour Guard were killed by the revenants. With his guardians dead Larion Ursus was successfully apprehended, and when the inner palace defences fell was taken into custody.
As control of the palace was consolidated the marines discovered that Deidara Ursus was nowhere to be found, along with Brother Lusmer of the Honour Guard and Anastasia Belladon - one of the coven witches.
Once the palace had been fully swept and secured Chapter Master arrived and began negotiations with Larion Ursus regarding his surrender of the throne.