Uriel Ventris, newly ascended to the ranks of the Primaris, leads warriors of the Fourth Company from the Indomitus Crusade of Roboute Guilliman to a world on the frontiers of Ultramar. Once a battleground against the orks, Sycorax is now under furious assault from an enemy of ancient times – the necrons. The Ultramarines have faced these baleful xenos before, but Uriel senses the hand of a foe from his own past at work on Sycorax, a tally unfinished and a debt to the Imperium finally come due. Trapped deep in a devastated city, Uriel leads the Swords of Calth into battle, and must adapt to his new incarnation as one of the Primaris – a challenge that will test his soul as much as it will test him as a warrior.