While the first book can stand alone, this is very much a sequel. You need to read the first book to understand what's going on in "Monster."

The first book ends with Baru making a terrible sacrifice to secure her power. This book picks up there and twists the knife further before moving on with the plot. Baru is sent on another mission, but a lot of what she's dealing with is other people conspiring to kill her or gain power over her. She is dealing with the trauma of her previous decisions, and it seems like this book represents a turning point for her. The end of the book though, makes me wonder if she's going to make another life-changing decision in the third book.

We get to see more of the world, and especially more of the Oriati people and culture. The world gets a little weirder than what we saw previously, and there is magic in this book that wasn't present in the first one. There is also the Cancrioth, which can't be described without spoilers, but it is definitely in the speculative realm. This book doesn't have the major twists of the previous one, but there are a few small twists, and the end is still powerful

In the first book there was some nuance about colonialism, but overall the colonizers were treated as evil and the natives were good. In this book, the lines are blurred a little more. Baru learns that the world is interconnected, and while the empire still does terrible things, its collapse could destroy civilization.

The first book dealt with sexuality, but I don't recall any actual sex scenes (just characters waking up in bed together, etc.). In this book, Baru can be more open about her attraction to other women so there are sex scenes, but they are not very explicit. There is also a major character who is non-binary, referred to with "they/them" pronouns.