Harry Potter and the Prisoner of Azkaban

(Reread, obviously.)
Where many people love this the most of all the Harry Potter books, PoA is probably my second favorite installment in the series (Sorcerer's Stone is number one). Then again, that might change as I work through the rest of the books. It HAS been quite a while since I've read the series!
This one has such great intrigue and mystery, taking it into a slightly more mature territory than the first two. This is such an amazing quality of the books that I can't quite put my finger on how it's done: they mature along with both their main characters, and their audiences.
The introduction of new characters (Trelawney, Lupin, and of course Sirius Black himself) is so welcomed. Each one has their own, completely unique voice and energy.
This book also has an incredibly satisfying ending scene.
I'm now going to listen to the Real Weird Sisters talk about this book on their amazing podcast, and then move on to the fourth!