A Brother’s Confession by Robbie MacNiven acts as a prequel short story to the forthcoming novel Blood of Iax and introduces the characters of Kastor and Polixis (geddit?), two Ultramarines Primaris Marines whose bond of brotherhood goes deeper than Chapter ties alone. Apothecary Polixis comes before Chaplain Kastor to make a confession, relating to his brother the tale of his last mission, and the sin he committed.
