Harry Potter and the Prisoner of Azkaban (by J. K. Rowling)

This third entry in the series is scarier and more intense than the last two -- and even more exciting: When he can't stand his relatives' tormenting any more, Harry runs off, only to be picked up by a magical bus and taken to the Leaky Cauldron Inn. There he learns that Sirius Black, who supposedly betrayed his parents, has escaped from the wizard prison Azkaban, and is coming to kill him. The soul-sucking Dementors, guards from the prison, are dispatched to protect him back at school, but Harry finds that whenever one comes near he can hear his mother dying.  But Black seems to get into the school anyway, Hermione and the new Dark Arts teacher each have secrets, and Ron's rat Scabbers and Hermione's new cat act strangely. When Harry obtains a map showing all the secret passages in the school, he makes discoveries about his parents, Snape, Black, and the new teacher. But what he learns may pit him against the Ministry of Magic.

J.K. Rowling has sidestepped the usual series-writer trap of sticking so closely to a successful formula that each book is just more of the same. With Harry about to enter adolescence, the series, too, seems to be changing; this entry is darker, more complex, and morally more ambiguous than the first two. As he is forced by the Dementors to confront his parents' deaths directly, Harry -- who was always so cool in the earlier books -- is more emotionally unstable. Unlike the static characters in other series, Harry is getting older, with all that entails.

Rowling is a master of careful plotting, and the author is rumored to have planned out the whole story of the series in advance, for a total of seven books. In this volume, her planning shows, and the complexity is so great that, at times, it even inspires rereading. Rowling knows her readers, but even as she stretches their intellect, she never loses them.