|Outcome||Pyrrhic Imperial victory|
| Imperial Guard Regiments
Order of the Valorous Heart
Order of the Black Sepulchre
Unrest had been growing in the Orpheus Sector for nearly a thousand years. Constant wars, such as the Haxan Wars and against the Apostate Heptad and the Dark Eldar Kabal of the Slaughtervane, had bled the sector dry and created economic discontent. In addition, a political crisis erupted when the dynasty that began with Arica Orpheus finally died out, resulting in the House of Laan taking power as Sector Governor. Immediately tensions over Tithes and the cost of the sector's ongoing wars flare into campaigns of assassination and revenge against the ruling nobility and Merchant Fleet chartist captains. Within a year, a full-scale revolt begins when the clans of the Drucillan Cluster overthrew their local Imperial rulers and declared their secession from Sector authorities. These rebels recruited many renegades to their cause and undermine the region's stability.
Feeling threatened by this turn of events, the ruling government of Amraphel brings in Khrave mercenaries to conduct a pre-preemptive strike against its rivals, only to have their new xenos clients devour their minds and control their bodies. Eventually, they are discovered and purged in an Adeptus Ministorum-led uprising.
As civil war and brushfire conflicts spread across the Sector, it is revealed that Chaos had taken hold in the nearby Haxan Sector. Imperial Guard Regiments are deployed into the region to bring it under control, but find themselves facing Daemons and hordes of Mutants along the rebels. Apollyon and Selakhar fall entirely under the sway of the Ruinous Powers. However, this threat serves to only unite the disparate and divided factions of the Orpheus Sector against the Forces of Chaos.
In the ensuing 'Orphean War of Faith declared by the Ecclesiarchy, a force of Zealots, Sisters of Battle, militia, Guardsmen, and pilgrims united by religious faith led by the Arch-Confessor Marduk. When the forces of Daemons, Alpha Legion, Night Lords, and Death Mongers are identified among the Rebels, the Ministorum forces are able to secure additional resources from the Imperium. Most important among these are the entire Angels Revenant Space Marines, the Adepta Sororitas Order of the Valorous Heart and Order of the Black Sepulchre, and a taskforce of Ordo Malleus Inquisitors.
By 921.M39, the War of Faith is effectively won by the forces of the Imperium when all Traitor-held worlds are either reconquered or laid waste to except one, the Chaos stronghold of Colkasth. The Hive World had been fortified into a living hell and its population used as raw materials by the Warpsmiths of the Death Mongers. Arch-Confessor Marduk claims the final victory for his own zealot and Imperial Guard forces, choosing to instead dispatch the Space Marine and Sorotias allies to destroy other fleeing traitor forces. However after all contact is lost with the Ecclesiarchy forces, the Angels Revenant Strike Cruiser Intercessor rushes to investigate only to be attacked by two small xenos craft of unknown origin. Destroying one attacker and driving the other off, the Space Marine vessel is badly damaged but nonetheless finds that the entire world of Colkasth had been reduced to a radioactive wreck. The Angels Revenant discover a few catatonic survivors on the planet. Colksath is forever afterwards named Saint Marduk's Bane, after the "martyred" Arch-Confessor himself.