The Blood Angels strike cruiser Sword of Baal hangs in orbit over the planet Niades, trapped by warp storms. Aboard, the ship's complement of Space Marines chafe at their inaction.

On the trail of their missing Captain, the Blood Angels deploy to the surface of Niades by Drop Pod. Their journey is not a smooth one, and they must regroup to explore the ruined city at the base of the docking tower.

While Ancaeus' surviving warriors follow Castia's Servitors through the under-tunnels of Niades, the Tech-priest explains her plan to the paralysed Captain Orpheo. High above them, in the inner sanctum of the Siren Tower, the Genestealer Cult's Magus tells her brood-kin the hour of their ascension is nigh.

Beset on all sides, can the Blood Angels of the Sword of Baal hope to prevail? Reeling from the brutal onslaught of the Aberrants, Ancaeus and the survivors of his squad must regroup, while Kazarion battles the grip of the Black Rage. In orbit, as the debris of the promethium hauler's destruction clears, the strike cruiser and its crew are immediately attacked by more flotilla ships. Somewhere beneath Niades' surface, the savagely wounded Orpheo discovers his fate.

As the Blood Angels on the surface of Niades cut a course through the entrenched Genestealer Cultists towards the signal from Captain Orpheo's beacon, the situation aboard the Sword of Baal goes from bad to worse.

The Blood Angels fight their way ever deeper into the evil that has corrupted the world of Niades, with new and brutal enemies assailing them on all sides. Can their strength hold in the face of such fearsome foes?

This episode takes us back to a time before the Sword of Baal arrived at Niades. Witness the might of an Imperial battlefleet at war, and the confluence of events which saw the Blood Angels seek safe harbour from the birth of the Cicatrix Maledictum....

In the cult's chambers high up in the Siren Tower, the surviving Blood Angels count the cost of their war with the cult. They are soon joined by Magos Dominus Castia-Theta-9, who offers them a chance to escape Niades.

The Blood Angels, reunited with Captain Orpheo, ascend to the heart of the cult's corruption - and in doing so, call down the wrath of the Magus. Meanwhile, the Primus leads hordes of cultists to surround the Sons of Sanguinius. Aboard the Sword of Baal, Livia will do anything necessary to ensure the cult cannot take the ship - even if that means destroying it. Yet even now, perhaps the Techmarine Hadrael offers slim hope of redemption.

The battle for Niades reaches its epic climax as Ancaeus, Kazarion and Orpheo confront the leaders of the Genestealer Cult. Can even the courage of the Sons of Sanguinius hope to overcome the monstrous might of the Patriarch? Even if they can, all will be for naught if Hadreal and Ignis cannot free the Sword of Baal from the orbital dock and stop the flotilla ships from spreading the curse of Niades to other worlds.