A war-weary Battle Group Praxis arrives at the Knight world of Kamidar, ruled by the Iron Queen Orlah, to return the queen's slain daughter and heir, who died fighting in Guilliman's name. In truth, the Imperium's mission here is twofold: to strip Kamidar of its resources in order to resupply the flagging armada, and prepare the Ironhold Protectorate to become part of the defensive Anaxian Line, a crucial bulwark for the Indomitus Crusade. With Kamidar having survived many years without the Imperium's aid, what should have been a simple reunion between allies soon becomes a vicious feud.

As division turns loyal souls against one another, the agents of Abaddon move in the shadows, seeking to manipulate this growing rift to their own ends. Can the Imperium bring itself back from the brink before it's too late, or will the Hand of Abaddon arise triumphant, halting the Avenging Son's reclamation in its path?