If you have not read Harry Potter and the Half-Blood Prince and do not want to know what happens in the book I would strongly advise you to wait until I post a new blog entry about something else because I'm going to be writing about major spoilers from the book and what I think about them.
You have been warned...all four of you.......
I'll start with the title. I spent most of the book thinking that I cleverly figured out that the HBP was Lily Potter, Harry's dead mum. It probably would have been too obvious if it was Lily. Slughorn, the new potions professor (Snape finally got his dream job of Defense Against the Dark Arts), said that Lily was one of his favorite students and was a natural at Potions and used unorthodox methods to work the potions. Harry seems to have an affinity for the HBP. Lily was at least muggle born, I don't remember if she was Half Blood.
But it was Snape, which makes more sense because Slughorn didn't talk about Snape all the time the way he did with Lily. And Snape was always the potions master and brilliant at it and Lupin had gone to Snape to help keep the werewolf in him under control. I don't know if this will have a larger impact in the series or it was just something to do for the book.
Speaking of Snape...
Here's what throws me about the big ending of the book: Snape murderers Dumbledore with the killing curse, the one that the only one who ever lived after being hit with it was Harry himself. But early in the book, like chapter two or three Snape is revealed to have been a Death Eater all along and that he fooled Dumbledore. He tells this to Draco Malfoy's mother (his father, Lucius, is now in Azkaban prison) and Beatrix Lestrange, the killer of Sirius Black (and torturer of Neville Longbottom's parents). To seal the deal, Snape agrees to take an Unbreakable Vow to help Draco Malfoy do whatever it is he is commanded to do by Voldemort. An Unbreakable Vow is one which the person bound by it must either fulfill or die. Breaking the vow will kill the bound wizard.
Why give this scene away for free? What I mean is that Jo Rowling has spent five books telling us that Snape is a good guy. He may dislike Harry and Harry's father and Sirius and pretty much everyone else, but he is a redeemed former Death Eater working for Dumbledore and the Order of the Phoenix. Why give away a scene like that telling the reader he is evil if Rowling will give us hints for five books that Snape, while sneaky and nasty, is a good guy and a protector?
Because he still is.
What if Snape then tells Dumbledore about what he vowed to do and Dumbledore agrees that he must go through with it no matter what the cost? What if that is what Hagrid saw Snape and Dumbledore arguing about? What if Dumbledore was not pleading for his own life, but rather for Snape to do it?
It's never shown on screen, but I think this is how it happens. Snape takes the vow to convince Lestrange and Malfoy that he still serves Voldemort. He is still under orders from Dumbledore to do this. Snape tells Dumbledore about the vow and about everything he learns from Malfoy. When the time comes Malfoy can't murder Dumbledore and if he doesn't Voldemort will kill him. If he doesn't, and Snape doesn't help, Snape will die from the Vow. Dumbledore pleads, just as he pleaded with Malfoy for Draco to leave Voldemort behind and let the Order hide him and Narcissa. But Dumbledore pleads for Snape to kill him as this will save Draco, keep Snape in place, and give Harry the last bit that he needs to finally be able to confront Voldemort and win. And live. So Snape kills Dumbledore. His reaction? Rage. Disgust. At whom? Not at Dumbledore, but at himself, at Malfoy, at everyone. Dumbledore was the only person to really trust Snape for years and Snape just had to kill him.
Now Snape really is outcast. Nobody will ever trust him again. He isn't a Death Eater but has to pretend to be. When he ran he could have attacked and stopped Harry but instead only blocked Harry's curses. Snape didn't strike out except to stun on his way out of Hogwarts.
My interpretation: Snape is conflicted and internally brutalized because of what he just did and he never turned his back on the Order and is still fighting Voldemort as he can and what was done was done with knowledge of Dumbledore and, dare I say, the blessing.
The other thing that makes me think this is that had Jo Rowling never revealed early on that Snape was still a Death Eater the murder of Dumbledore would have been even more shocking and would have been a true betrayal. But now we're expecting it and Rowling never gives something this big that early in a book unless there is a reason for it.
Side: I also think that Draco will be redeemed, that he'll turn away from Voldemort. He won't be a major player, but he'll betray Voldemort.