There is a totem. From it comes a black mist. Mist consumes the totem, the mountain, the forest and the twin-headed eagle within. Without the eagle it covers the world and reaches out to the stars.
The planet Castobel is under siege from elements of Tyranid Hive Fleet Dagon. The Deathwatch has been tasked with escorting high value resources from an imperial outpost crawling with Tyranids.