Emperor Mage

The worldbuilding focuses heavily on Carthak and almost completely ignores Tortall except when drawing some comparison between the two nations. It’s uncomfortably fascinated with slavery in Carthak, specifically with how it is carried out in the palace. It’s yet another white savior narrative (e.g. THE WOMAN WHO RIDES LIKE A MAN) in book three of a Tortall book. This is a bit subtler, since Daine had no intention of messing with the Carthaki way of life, slavery and all, but it turns out that some of the other characters have been actively involved at getting slaves out of the country. Daine’s goddess-driven involvement serves to mess things up for the Emperor, making Carthak much friendlier to Tortall than before their trip. Daine’s bonds with animals provide conversational opportunities for her to draw comparisons between slavery and the caging of animals. 

This finally addresses the mentions of the Carthaki Emperor’s involvement with the recent influx of immortals, but it mostly does so by introducing the Emperor himself at long last. It has a new storyline involving a Tortallan delegation to Carthak for peace talks, with Daine alone to heal the Emperor’s birds, if she can. A very major thing related to Daine is introduced and resolved here when the Badger passes along a temporary power at the behest of a Carthaki goddess. It leaves several things for later, such as Daine’s growing understanding of her parentage. The trick is that it doesn't really move anything forward (except for Daine almost beginning to understand how much Numair cares for her), so it's very skippable. I actually think that going straight from the first to the fourth book in the quartet might work well because then it wouldn't feel as weird with Numair being more attached to Daine as she grows up.

It can stand alone enough that someone could probably read just this book and have a good time, understanding almost all of what happened. It would help to have read either of the first two books in the quartet (benefitting more from the second book), but this is a very episodic series and doesn’t require the other stories in order to make sense.

The plot centers around Daine and a Tortallan delegation visiting Carthak for peace talks, but Daine gets some divine attention and is used to send a last-chance warning to the Emperor before things get very bad for him. There's also a persistent narrative about the presence and treatment of slaves in Carthak, since Tortall hasn't had slaves in a few centuries. At several points the narrative ends up just describing a bunch of dinosaurs, along with the magical means of learning about their lives based on fossils and the work of seers. This is a pretty strong self-contained narrative, it's just in the context of yet another instance of (very white but not homogenous) Tortall claiming moral/cultural superiority over another (primarily brown/black) country that this looks a bit off. I wish there were more named characters of color who aren't enslaved, since I'm pretty sure the only ones are the Emperor and his heir, and one of those two is a villain.

It's a very weird anti-slavery PSA with resurrected dinosaurs, completely skippable within the series.