Fall of the Angels Vigilant

The Fall of the Angels Vigilant was a lamentable event that occurred in the history of the formerly Loyalist Angels Vigilant Space Marine Chapter, that eventually fell to the predations of the Ruinous Powers, which resulted in the Chapter's corruption by Chaos and eventual excommunication.

Background
Roughly a decade prior to 236.M39, the Chapter's home sector was faced with the biggest xenos invasion in it's history. The sector's Battlefleet and Astra Militarum forces were eventually swept away, many of the populated planets where destroyed, and soon the xenos host had arrived at Mavros. Because the Sector was in an isolated and unimportant part of the Galaxy, the sector's call for help was ignored by the wider Imperium. The Angels Vigilant were left to stand alone against the impending xenos invasion of their homeworld.

As the xenos army made planetfall and swept through the Mavros countryside, the Angels Vigilant vanguard forces began to rapidly succumb to the Black Rage, and the Daemon artifact once again called out to Elymas. This time, the Daemon demanded that the Chief Librarian take him to Hadrian Nero, the Chapter Master of the Angels Vigilant. The Daemon revealed himself to be a Greater Daemon of Chaos known as Azazel, and promised to save the Angels Vigilant from annihilation in return for the Chapter turning their back on the Emperor and serving the four Ruinous Powers. With much of the Sector already destroyed and half his Chapter either dying in battle or succumbing to the Black Rage, the Chapter Master saw no reason to reject the Daemon's offer. The Imperium had abandoned it and so the Angels Vigilant, now known as the Void Stalkers, would abandon the Imperium.

And so the Void Stalkers, imbued with the diabolical powers of the Warp, began to push back the xenos with savage fury. The battle was finally won when "Arch-sorcerer" Elymas freed Azazel from the relic and summoned him into realspace. Together with their Daemonic master, the Void Stalkers were able to slaughter the xenos race to extinction.