Harry Potter and The Goblet of Fire- J.K. Rowling

This was the longest book in the series so far. It’s also the first time the movie has really strayed at all from the book version, and even so it was only concerning minor details. The build-up of the climax goes until almost the very end of the book before it is revealed who is working at Hogwart's as a traitor for Voldemort. I especially liked that this story validates Harry's credibility as someone special beyond his passive defeat of Voldemort as an infant.