This is a somewhat different approach to the Horus saga, as it focuses primarily on the Imperial army and what the reader would consider "normal" humans (as normal as humans of today could seem 30000 years in the future in regions far from here). The typical Emperor Astartes Legion is in more of a support role in this novel, and it took me about half of the book to adjust my thinking along those lines as the first six books was more of Legions' adventures literally thrown right in one's face. The basic premise: an alien race has the ability to forsee the coming Galactic Chaotic Civil War between humans and tries to implant a spy (John Grammaticus) into the Alpha Legion to warn them of the apocalypse in hopes the Alphas can prevent Chaos from ruling by helping to PROMOTE civil war and allowing Chaos to basically burn itself out quickly. This is a paradoxical twist that can be hard to digest for even dedicated Horus fans. I enjoyed the book, but here's hoping that future Horus novels further the saga more.