The Battle of Castobel
The Grey Knights are a mysterious Loyalist Chapter of Space Marines specifically tasked with combating the dangerous daemonic entities of the Warp and all those who wield the corrupt power of the Chaos Gods. The Grey Knights act as the military arm or Chamber Militant of the Ordo Malleus, the Daemon Hunters who form the oldest branch of the virtually omnipotent Imperial Inquisition. The Grey Knights’ fortress-monastery is based on Titan, the largest of the moons of the gas giant Saturn in the Sol System that is kept as a private preserve of the Inquisition. Unlike the other Astartes, every Grey Knight is a potent psyker, yet no Grey Knight in the 10,000 standard years of Imperial history has ever been corrupted by the Ruinous Powers of Chaos.