Xenos (Eisenhorn #1) by Dan Abnett (goodreads page)
Published: 2015
Genre, sub-genre: Sci-Fi: franchise (warhammer 40k)
Pages: 416

Notable aspects:
Warnings: medium gore and wartime suffering

1 minute summary
The Inquisition moves amongst mankind like an avenging shadow, striking down the enemies of humanity with uncompromising ruthlessness. When Inquisitor Gregor Eisenhorn finally corners an old foe, he is drawn into a sinister conspiracy full of dark powers and daemons racing to recover an arcane text of abominable power.

My rating: 4/5
1 sentence review: Full of action and interesting world-building, Xenos is a great rollicking space mystery and adventure.

Pros: great action, excellent world building, nicely crafted characters.
Cons: a bit thin on both information and immersive details.

Good for readers who: enjoy warhammer 40k lore/games and appreciate interesting world building
Not so great for readers who: like deep-dives into fully-fleshed universes

I typically don’t do full-fledged reviews for franchise books, but Warhammer 40k books are the exception because I know that the lore has many fans beyond those who play the games. Nevertheless, I have difficulty writing reviews for WH40k books because I already have knowledge of the universe, and I’m aware that other readers don’t. So take my review with a grain of salt.

Pro: great action. There’s a lot of great fight scenes that happen in Xenos; the guns come out right at the beginning, and they don’t stop for much of the book. What I like is that not a lot of it is repetitive, which can happen in SFF when you have, say, combat that always happens with swords and fists. One of the great things about the WH40k universe is that there are so many types of weapons, from psychic powers to insane guns and monstrous beasts. A fight scene is almost never the same.

Pro: excellent world-building. When humanity is spread out over tons of worlds, then falls out of contact for many generations, only to be reunited later, the potential for world building is great, and Abnett doesn’t disappoint. Each society is wonderfully unique and molded ingeniously to their specific world—and that’s only the humans. It’s fascinating to world hop in Xenos.

Pro: nicely crafted characters. I wasn’t expecting a first-person narrative in a 40k book. I always think of the universe and the characters in it as mindless war/fighting machines; it’s always kind of shocking to see they are people, with joys and fears and friendships. Abnett builds Eisenhorn, his retinue and other inquisitors as people in a religious order that’s not monolithic. He brings a humanity to them that makes the story and its conflicts much more meaningful despite the overall grimdark tone of the universe.

Con: like most franchise books, it’s a bit thin on information and immersive details. I’ve heard many non-WH40k game fans say they enjoy this book, and I suppose you should take their word on this more than mine. But I thought that the book didn’t really explain some important details, such as the warp, the chaos marines, the emperor’s importance to humanity and the inquisition. I think that laying the groundwork for that would bring a new reader fully into the fold so they could understand the universe—and, by extension, the events of the book—more clearly. But I will freely admit that these details might not actually be all that important to enjoy the story, and it’s just my own knowledge of that information which leads me to believe it would make the book more vivid.

Overall: A great, accessible sci-fi adventure all on its own, Xenos brings a great, vivid sense of humanity to the Warhammer 40k world.