The story
The wizarding world becomes visibly larger in the fourth book. The Quidditch World Cup introduces international magical communities, while the Triwizard Tournament brings students from Beauxbatons and Durmstrang to Hogwarts for a dangerous competition between schools.
Harry is unexpectedly entered as a fourth champion and must survive a sequence of tasks involving dragons, the Black Lake and a magical maze. What initially looks like the biggest school adventure yet gradually reveals itself as a carefully arranged trap.
Goblet of Fire marks the point where the central conflict can no longer remain distant background history. The final act changes the direction of the entire series and establishes the political and personal stakes that dominate the remaining books.