This is the conclusion--the triumphant conclusion!--of the City Trilogy. It's probably my favorite Yep so far, this trilogy, and City of Death doesn't disappoint. It brings together the plot and the themes of the previous books, while still introducing fun new elements. I have complained several times here about alternate histories in which nothing changes, and this is definitely not one of them--the Kushan Empire makes a huge difference in how this world has developed, and magic makes an even bigger one. A few elements have the same name--San Francisco and Hawaii, for example--but a world that already has dragons and griffins will react to airplanes differently, and this one does.
One of my favorite parts of this is that Scirye's parents show up and act like parents--they want to protect their young daughter, they are loving, good parents--and this interacts in difficult ways with the fact that Scirye is a hero who needs to save the world. Having absent parents was not just a genre convention here, it was a thing that Yep dealt with directly in multiple ways--including making some of the parents present again, and making them realistic people and decent parents without letting them take over the kids' story. Go that.
There are a few places where the characters who are angsting secretly get a bit repetitive, but the chapters are so short and so fast-paced that the few repetitive elements don't really make a dent in how much fun the book is. I recommend the whole series. I started with book two and went back to book one before reading book three. I don't recommend starting with book three as the ideal course, because so much of it is the consequences and wrap-up from the previous ones, but it's a kids' book--I bet you could do it. A lot of kids' writers write so that you are clued in to what has gone before in a plottish way, and Yep is no exception. It's just the emotional impact that would be somewhat lessened, I feel.