This book is so much better than it has any right to be. Look, I love 40k, especially the older stuff, and there is some bad fiction out there set in that universe, including some by Abnett (not a particular fan of Gaunt's Ghosts). That said, this is a solid read - it's not just a good 40k novel, it's a good standalone novel. And that's a rarity. I was on the fence through the first act on whether to give this five stars, which is something that I try not to do unless a novel truly excels; too many fans/haters out there either give 1 or 5 stars to everything.
The second half of the book kind of lost its focus, which is why I downgraded it to 4, but this is a great book - imaginative, decent characters (a little flat, but that's because there are a lot of primary characters, and it's a novel about stuff happening, not how people felt about it), and next-level world-building.
The cast:
Ravenor himself, trapped in an armored life-support suspension chair. He's blind, mute, and personally immobile due to an accident in the preceding Eisenhorn trilogy, but remains a formidable psyker. He communicates psychically, giving advice, warnings, and occasionally "waring" (taking absolute control) of his agents, primarily from orbit.
Kara Swole - acrobat turned agent
Harlon Nayl - smart muscle, not much to be said. Close with Kara Swole.
Patience Kys - low-level psychic operative
Carl Thonius - the tech guy, and personal coward. Abnett's setting him up to do a fall to Chaos due to using Chaos-tainted drugs to deal with the trauma of having his arm chainsworded off and reattached.
Zeph Mathuin - nearly indistinguishable from Nayl, I think he's there to kill off to give some narrative weight to something later.
Wystan Frauka - the blank, a chainsmoking creep. He's got a limiter, which allows him to turn off his psychic null-field.
Zael - dumb hive kid, the Chaos drugs awakened latent psychic power. Might be a precog. Hilariously refers to Ravenor as The Chair.
Magistratum
Kinsky, potent but unschooled unsanctioned psyker
Madsden, their leader
Ahenobarb, dumb muscle
The plot:
Inquisition agents led by their Inquisitor Ravenor are undercover investigating a new drug called flects. The drug is suspected to be of Chaos-origin, and has a euphoric and addictive high. It takes the form of small glass fragments that show visions to the user. Normally an Inquisitor wouldn't bother with something as small as a drug trade, that might even fall below the notice of the Adeptus Arbites, but the Chaos taint makes it notable.
A note about the world-building on Eustis Majoris, the planet at the beginning - it really nails the squalor of an Imperial world fallen on hard times, and they're not great places to begin with. Acid-rain strong enough to burn flesh, the poorest feasting on insects, large segments of the hive cities are abandoned, an absolute dearth of law and order . . . It's like Blade Runner had a baby with RoboCop, and I'm loving it. Just as an example, while tracking the flects, they come across a woman with a filthy aquarium, with an unknown shape inside moving, and you think it's going to be someone so far gone that they don't realize the filth they're living in. Inside is most of her brother - he was injured in an industrial accident, and is kept alive, but only just, and the minor settlement she got isn't enough to change his nutrient fluid.
The team is each tracking a lead - Swole kills a group of gangers, and is arrested, Nayl finds a user and forces him to take him to his dealer, Kys and Thonius show a bit of the uppercrust society as Kys flirts with a rich ass and gets the name of his dealer by revealing herself as an Agent before he overdoses. This draws the attention of the Magistratum, and Ravenor is chased away by a potent psyker.
The leads point to a gladiatorial arena, the Carnivora, where exotic beasts are fought by gladiators. Nayl and Mathuin sneak in by posing as deliverymen, Swole as an acrobat, and Kys acts as a highborn slumming it with gangers who pay her way in. It, predictably, goes to shit - they capture their next lead, but are discovered and must declare themselves to the Magistratum. This is about where the novel starts to drag, just one too many jumps in the investigation in my opinion.
From there, they begin tracking the ship the October Light and its role in the exotic beast trade, having realized that the flects are coming in that way. The Magistratum agents accompany them, they proceed to find beast moots where the creatures are sold to fill the bellies of the Imperium, but Kinsky uses psychic powers which is detected by the moot boss's pet psyker. This results in the team running for their lives, and the normally behind-the-fray Thonius loses an arm. He'll start using flects to deal with the trauma, with absolutely no future consequences I'm sure.
They proceed up the chain into a lawless region called Lucky Space, and it's quickly revealed to be a trap - the Magistratum agents were trying to make Ravenor disappear in Lucky Space to avoid drawing attention. The actual conspiracy is about the planetary governor dealing in heretical tech, and the flects were only a sideline. They do in fact come from a Chaos-tainted world, and are basically solidified Chaos left behind when a warp storm killed everyone. Most of the team is captured, with Swole catching a ride on the outside of a bulk lifter filled with big game hunters in the service of whoever is the next link in the chain until it docks with a dubious spacesuit, Frauka is killed, Nayl is captured Kys and Zael are loose on the ship, Swole rescues them and they engage in a running battle, Ravenor's psychic limited is removed and he fights Kinksy.
A note about that - this is a pretty cool sequence, with both psykers taking on various guises in the mental landscape, and occasionally breaking into reality. It's a neat way to handle mental combat.
Ravenor is getting the worst of it as his chair was damaged by one of the conspirators, but Frauka gets back up (not dead after all) and kills Kinsky while he's distracted. The team is presumed dead by the conspirators back on Eustis Majoris, and they've worn out their welcome with their ship's captain, and engage the services of a hilarious little dwarf that uses words improperly or just makes them up. Looking forward to a bit of comic relief in the next book.
I know I said it up above, but this investigation is one jump too far. Too many villains, and I think the book focused on the least interesting ones. Still, it's an excellent book, for the world-building and swashbuckling adventure.