The premise is Martian breakaway faction, the Laconian Empire has gained access to a protomolecule-based orbital shipyards they've mastered the technology of. Having set up their own colony on Laconia, they've build up their Navy and invaded the Sol system with unbeatable superweapons. If it sounds familiar, that's because it's the plot of STAR WARS: THE FORCE AWAKENS. They also have some WARHAMMER 40K elements with an immortal (or so he thinks) God-Emperor and Space Marines in blue armor with an eagle on it in what's probably a deliberately homage.
I like the Laconians as enemies because there's nothing more satisfying than killing Nazis, except maybe killing Space Nazis. I also like how they're portrayed as intelligent savvy villains despite the fact they have severe flaws. Duarte is so completely full of himself that he actually believes that making himself a god with the protomolecule (revealed in the first chapter) is a viable strategy. He plans to rule humanity forever like Leto Atreides and think he's wise enough to believe this will lead to an eternal paradise.
Santiago Singh is a great counterpoint as he's a child who grew up on Laconia and has drunk the fascist Kool-Aid to the point he believes the universe works exactly like the propaganda says it will. Watching him have a slow nervous breakdown as people continually try to protect their freedom and are willing to die rather than submit is surprisingly effective. The fact he's a loving family man who isn't normally a monster but becomes one, Heart of Darkness-style, makes the story all the more interesting.
Unfortunately, the rest of the book doesn't quite live up to this premise. Holden and the crew haven't changed quite enough for me to believe it's been thirty years and they've changed too much in other ways. Clarissa and Amos have been effectively (but platonically) married for 30 years but we never get to see any of that relationship. Alex got married, had a kid, and got divorced without us ever meeting them. They're also still doing the same jobs they were before the time skip. I feel like they should have halved the time skip and just had ten to fifteen years pass. It would have been a lot more believable.
Bobbie is the character I actually enjoyed seeing the most growth with but the problem is a lot of that growth is thwarted. She's ready to become the captain of the Rocinante after Holden retires, head up the resistance, and do all manner of exciting things. It's just, well, almost all of them get thwarted by Holden not retiring or giving up the captaincy because of the new threat. It's also a shame she didn't get with Alex.
The character I most enjoyed the treatment of was probably Drummer. She's ascended to become the head of the Transport Union (and there's no sign of Michio Pa-thank God) and more or less has Fred Johnson's place. She's also been happily married this entire time so we have changes like her concern for them, a new concern for Inners, and other developments. Fred Johnson's absence is considerable for the book's dynamics as is Chrisjen Avasarala. Still, she manages to put a good face to the catastrophe.
Overall, the book is an improvement over BABYLON'S ASHES and I am eager to see where the story goes. I'm not a huge fan of the threat which the books have been building to and hope they continue with the politics-based threat of the Laconians but, overall, this was a solid piece of sci-fi literature. It's just a bit predictable the crew of the Rocinante would IMMEDIATELY begin organizing a resistance to the Laconians.