I finally made myself read this book, despite being a bit intimidated by the 446 pages. I should have known that it would be an enjoyable read and not seem to be nearly that long. Diane Duane is a word weaver, and a very good one. This book is part of the Errantry universe that began with So, You Want To Be A Wizard. It wasn't until I was well into the book that I realized there were others that came before it. However, Duane has set this one up to stand on its own, so while I suspect the reader might have a broader picture of wizardry in general by having read the other books first, it doesn't detract from enjoying this one.
The main characters are New York cats that also happen to be wizards. Their job is to maintain the worldgates that are located in the New York subway system. Something is interfering with the workings of the worldgates and it's up to Rhiow and her team to find out who and how to stop them before they open the gates to allow the sentient dinosaurs from ancient days to pass through to modern Earth.
The story is well-told. Read it, and you won't look at cats in the same way you did before.