Harry's fifth year at Hogwarts is even rougher than years one through four. Even before it starts, he and his porcine cousin Dudley get attacked by Dementors, a surprising event in the supposed safety of Privet Drive. Harry behaves heroically, but gets in serious trouble for using magic in the muggle world; he gets brought up on charges before the Ministry of Magic.
He gets out of that scrape, thanks to some clever and resourceful defenses by Headmaster Dumbledore. But things still aren't good: Harry's haunted by dreams that make his famous scar throb. His claims about the return of Voldemort are widely disbelieved, especially in the Ministry of Magic. Dumbledore is also put on the defensive: the Ministry forces Dolores Umbridge into Hogwarts, and she's very interested in tormenting Harry.
It's the longest Harry Potter book (870 pages), but it continues to be a good yarn. Once again, Harry survives; but just as in the previous book, there's a dreadful loss at the climax. A overarching theme is the refusal of bureaucracy to react effectively to menace; wonder if Rowling is trying to say something about the real world there?