The scattered worlds of the Elara's Veil nebula were once protected by the oath of unity sworn by three mighty Chapters of the Adeptus Astartes. The Star Scorpions were undone by flaws in their genetic coding. The Celestial Lions were ravaged by the Inquisition for sins they did not commit. Now, after hundreds of years, only the Emperor's Spears still keep their vigil. They are barbarian watchmen against the Outer Dark; bloodied but unbroken in their long duty.

Amadeus Kaias Incarius, a brother of the Mentor Legion, is commanded to cross the Great Rift and assess the Spears' war-readiness, only to be drawn into the chaotic plight of a depleted crusade on the Imperium's benighted frontier. The decisions he makes, far from the God-Emperor's light, will decide the fate of the war-torn Chapter.