(Click the character infographic to download.)
House: Gryffindor, 4th Year
In the previous three Harry Potter books, Hermione's character has been defined by one word: nerd. Sure, she's gotten a lot less finicky about following the rules over the years. But still, when in doubt, you can generally find Hermione in the library looking stuff up. (A trait we truly admire, by the way). But, in Goblet of Fire, Hermione gets a couple more adjectives: politically active and drop-dead gorgeous.
Sympathetic but Stubborn
From the beginning of Harry Potter and the Sorcerer's Stone, Hermione has been called a know-it-all. That know-it-all streak comes out again in her founding of S.P.E.W. – the Society for Protection of Elvish Welfare. Now, we do think Hermione is half-right about the way wizards treat house-elves. We see Dobby get horribly mistreated by the Malfoys in Harry Potter and the Chamber of Secrets.
But Hermione takes Dobby's example and insists it must be true for all house-elves – even when she sees Winky with her own eyes, weeping hysterically when Mr. Crouch frees her against her will. Hagrid, who knows plenty about magical creatures, tells Hermione that freeing the house-elves would "be doin' em an unkindness" (16.157). But Hermione is deaf to his protests, even though others have already said the same. Her heart is in the right place, but she's too stubborn to admit to anything that doesn't fit her worldview.
This is something J.K. Rowling admits to knowing about personally:
My sister and I both, we were that kind of teenager. (Dripping with drama) We were that kind of, "I'm the only one who really feels these injustices. No one understands the way I feel." I think a lot of teenagers go through that. (source)
Because J.K. Rowling understands what it's like to be fired up against injustice, she writes Hermione with a lot of sympathy. It's painful for Hermione to confront the fact that 99% of the world – including her best friends and the house-elves themselves – don't agree with her. That said, Hermione really should get off her high horse ASAP – which doesn't happen in this book, really.
(Book) Worm → Woman
What does happen to Hermione in this book is that she suddenly gets beautiful. Viktor Krum notices this transformation long before her nearest and dearest, Harry and Ron, do. Viktor starts hanging around the library just hoping to catch her eye. Indeed, they become close enough that Viktor Krum asks Hermione to the Yule Ball, and to come and visit him in Bulgaria over the summer. By the end of the novel, Viktor comes specifically to say good-bye to Hermione before returning to Eastern Europe, so it seems like their fling might keep going.
At the Yule Ball midyear, Harry and Ron's eyes finally catch up with their brains. Hermione appears totally unlike herself: her hair is "no longer bushy but sleek and shiny." And she's "holding herself differently, somehow – or maybe it [is] merely an absence of the twenty or so books she usually had slung over her back" (23.75). No longer a bushy-haired, big-toothed child, Hermione suddenly looks like a lovely young woman. This excites a whole bunch of feelings in Ron that he's clearly not ready to deal with; one problem with being a fourteen-year-old girl is that a lot of fourteen-year-old boys haven't quite caught up to you yet.
Ever the Clever Sleuth
But amidst this fog of S.P.E.W. politics and hormones, Hermione is still Hermione. She adores a good puzzle, and her biggest puzzle this year is Rita Skeeter. When Hermione starts screaming at Rita Skeeter after the journalist publishes a nasty article about Hagrid's half-giant blood, Rita warns her not to be "a silly girl" (24.151). After Hermione crosses Rita publicly, Rita Skeeter gets back at her. She finds out some private details about Hermione's relationship with Viktor Krum – that he wants her to go to Bulgaria with him over the summer – and publishes them in the paper while implying that Hermione is breaking Harry's heart. You know, just to add icing to the cake.
Hermione doesn't care about her reputation as a heartbreaker, but she does start getting a lot of dangerous hate mail from people who think she's "a wicked girl" (28.58) for stringing along Harry Potter. And how in the world did Rita Skeeter overhear Hermione's private conversation with Viktor Krum? This run-in with Rita Skeeter is yet another reason for Hermione to seek out the secret of the loathsome journalist.
Hermione continues to be brilliant: she's clearly the brains of the trio. She's the one who teaches Harry to use a Summoning Charm just before his first Triwizard Task. And when Harry is preparing for the third Triwizard task, Hermione drags out as many books as possible to help him master useful curses and hexes. Hermione is a mad genius, and we'd love to have her as our best friend too.