 It describes the rise to power of Horus Lupercal, Primarch of the "Luna Wolves" Legion of Space Marines, and the most versatile and favoured "son" of the Emperor.The Emperor has recently appointed him Warmaster, overall commander of Imperial military forces, while also leaving him in charge of the rest of the Crusade; the Emperor meanwhile returns to Terra, where in relative isolation he undertakes a secret project to which not even Horus is privy.The focus and perspective of the novel centres on a Space Marine Captain, Garviel Loken, leader of the Luna Wolves' 10th Company.