The Cadian 102nd has been picked to spearhead the break of the siege of Serena 4. Serena 4 was originally a pleasure world that was overtaken from with-in by cults and reinforced by off world forces.
The Imperial planet Castobel is under assault from the dreaded Tyranid Hive Fleet Dagon. The Imperial garrison has crumbled and sensitive information must escape and get off world.