"Legion" is the 7th book in the Horus Heresy series. This is my first time having read it and it's truly a mind-bending, somewhat confusing, very unique, and very different story than the other novels. But if you have even a smidgeon of knowledge of the XXth Legion Alpha Legion then you realize it is par for the course. Welcome to the Hydra. A secret unit, wrapped in a mysterious reputation, and an enigma to deal with.
For any of that to make sense, without true spoilers, here is a wee bit of background- the first Primarch found by the Emperor wasn't Horus Lupercal (Luna Wolves) but, actually, Alpharius. Also unique for the XXth, unknown to few save the Emperor, Constantine Valdor General of the Custodes, and Malcador the Sigillite., is there are actually TWO Primarchs, Alpharius and Omegon.
Why all the fuss? The Emperor chose three Legions (called the Trefoil) that he kept separate from the other Legions. These were the Space Wolves (The Emepror's Executioners), the Salamanders (haven't a clue why other than their view on humanity), and finally the subject of this novel, the Alpha Legion. They are experts in infiltration, covert operations, misdirection, and diversion tactics, and their armies contain many human operatives who work in close conjunction with their Astartes handlers.
The novel "Legion" looks at this covert Legion through the eyes of the Geno Five-Two Chiliad Regiment of the Imperial Guard. They have been battling to take the planet of Nurth. The story starts with Peto Soneka’s Dancer company being ambushed, as Hetman Hurtado Bronzi of the Jokers company watches helplessly. But his best friend Peto's life is rescued by a last minute intervention by a unit of Astartes making Peto the lone survivor of the ambush. These two Hetmen will find their fates intertwined with the Alpha Legion. Side note, I noticed the descriptions of the Alpha Legion being clad in purple and silver highlights. This is a common trick played by the Legion, which has also used liveries of pale grey, gleaming steel, veridian, dull bronze, sable, indigo, amaranth, and azure blue (the mainly associated color in 40K times)—both in main and combination, yet the Legion has also gone into battle without emblems or markings of any kind; a faceless, anonymous army of killers without distinction or division in its ranks. This is a VERY obfuscatory Legion.
I enjoyed seeing things from the viewpoint of the Imperial Guard soldiers, and also the Senior Command structure of the Astra Militarum as exemplified by Lord Commander of the 670th Expedition Fleet, , Teng Namatjira, who has come to the theatre to personally chastise the failing Commanders of the Nurth campaign. A cool nod to the lore to include the elite Lucifer Black soldiers as the Lord Commander's personal guard. Along with Namatjira, another character who has appeared in the theatre is the Imperial Intelligence Agent Konig Heniker. As a 40K- lore fan, I enjoyed this interesting look at some different parts of the Imperium and how they work in a campaign, as well as the internal politics of the human soldiers.
As interesting as all of that information was, we must remember that this is an Alpha Legion novel. It gets even more confusing as you learn that Heniker is not what he seems, though he IS a superb operative. His real name is John Grammaticus. On top of his superlative spycraft, he has two other advantages. One is that he is one of the most powerful psykers humanity has ever produced. Two is that he is a Perpetual, a human gifted with immortality. On top of all this we find he works for a mysterious secret organization called the Cabal. Even better? The Cabal consists of various xenos races, including the Eldar, that have a proposition that Grammaticus must present to the Legion.
The coolness of this novel is that as the standard Guard units are fighting a campaign with pressure coming from the Lord Commander, while this covert intelligence war is occurring. But as the Nurthene campaign continues there are dark signs of magic being brought to the battlefield. This conflict is where the first signs of Chaos are manifesting and this will lead the Alpha Legion to meet with the Cabal and learn the dire warning they deliver about the future and the doom of humanity, this is where the Alpha Legion falls to Chaos and sides with Horus. Or did it? What is the mission of the Alpha Legion in the events to come? Even after reading this superb book, I can honestly say I still have many, many questions still. Welcome to the Alpha Legion. You didn't see a thing.