This book is the second foray by veteran Black Library author Dan Abnett in the Horus Heresy series, and the seventh book in that series overall. His other efforts include works concerning the Imperial Guard (the Gaunt's Ghost series) and the Inquisition (both the Eisenhorn and Ravenor novels). Set in Games Workshop's rich, gothic Warhammer 40,000 (40K) setting, it benefits from 20 years of accumulated canon and imagination. This novel tells the tale of the 20th Space Marine Legion, the Alpha Legion, its Primarch Alpharius, and its network of operatives and spies.
Unlike most of the other Horus Heresy Novels, this one does not use the Marines as the primary point of view. Instead we see the tale through the eyes of members of the Imperial Army, primarily members of Geno Five-Two Chiliad, genetically engineered warriors left over from the Emperor's unification of Earth, essentially primitive prototypes for the mighty Space Marines. Peto Soneka, a "het" (translation: Captain) for one of their units is the most compelling character, but he's joined by a host of others that have equally believable abilities and motivations. Writing interesting characters has always been one of Abnett's strong points.
The beginning, usually one of Abnett's strongest points, stumbles in this novel due to an excess of odd terms that aren't easily defined by context. Where he usually weaves a compelling and immersive setting early on, it's difficult to maintain suspension of disbelief when you're wracking your brain in an attempt to figure out what some obtuse term actually means.
Fortunately he settles down into his typical excellent pacing after the first two or three chapters, and his action writing is as strong as ever. By the time you've gotten a third of the way into the book, you've forgotten the ragged beginning and can't wait to get to the next chapter. Particularly compelling is the view of the Marines of the Alpha Legion through human eyes. They retain their mystery and ability to inspire awe throughout, unlike some of the other books of this series. He really captures the intrigue, deception, and pragmatism of the Legion and mirrors it in many situations throughout the novel.
The climax and ending, typically one of Abnett's great weaknesses, works far better in this case than most of his other plots. It's not flawless, but as the deceptions within deceptions begin to unravel, the final choices are both interesting and unexpected. To say anything more might spoil the fun!
In short: if you can make it through the first few chapters, the rest of the work is well worth the price of admission, and is a refreshing change from the typical grind of "Legion goes bad except for a few good guys who try to fight the tide" that is typical of the other Horus Heresy books. Highly recommended for 40K fans, and still worth a look from general sci-fi readers.