A vast galaxy stretches on, and the faithful to the God-Emperor honor Him in countless images. Spiral Dawn is one of those countless sects approved by the Imperial Cult. But when a group of pilgrims arrives at Redemption—the Imperium’s temple-planet where the sect was born—they find not a quiet harbor of instruction and holiness, but a hell thick with ash clouds, where the founders of their order and the unusual regiment of the Astra Militarum barely manage to coexist. As tension grows between the “peaceful” sectarians and the superstitious guardsmen, the newly arrived gradually reveal the dark secrets hiding in the very heart of their religion.