Harry Potter and the Prisoner of Azkaban (Harry Potter #3) by J.K. Rowling
Another clever story, with much more backstory coming to light and characters beginning to deepen. We begin to see how dark the wizarding world can still be even after (or between?) Voldemort, what with Azkaban and the Dementors. Even Dumbledore can't do everything... And Lupin is intruduced, possibly my favorite character. What a good book. What a good series.