The war for the fate of humanity continues. Although the outer defenses have fallen, the walls of the Palace itself remain intact, as Rogal Dorn, the Praetorian of Terra, uses every trick and deception known to him to keep Horus's vast armies at bay. In Perturabo, Dorn faces an opponent worthy of his skill. The decisive battle for the Lion's Gate spaceport is at the very center of this conflict. With it at their disposal, the traitors can bring their most destructive weapons to the surface of Terra. Dorn knows that the spaceport must not fall. But with enemies attacking from all sides and the activity of the Neverborn drawn to the carnage, can the Empire's defenders prevail?