For millennia, the Shieldworlds of the Cryptus system have stood sentinel beneath the deadly stars of the Red Scar, defending the gateway to the Blood Angels home world. Now, an enemy has come who threaten to tear the Cryptus system apart and carry on to Baal itself – the monstrous tyranids of Hive Fleet Leviathan. The brave soldiers of the Astra Miltarum stand against them, shoulder to shoulder with the zealous warriors of the Adepta Sororitas, and on Baal the Blood Angels marshal their forces, commanded by one of their mightiest, Captain Karlaen – the Shield of Baal.