It was nearing midnight and the Prime Minister was sitting alone in his office, reading a long memo that was slipping through his brain without leaving the slightest trace of meaning behind.
Plot: Harry is asked by Professor Dumbledore to help him attract a new teacher to Hogwarts. Horace Slughorn is the man, but once they arrive at Hogwarts, Slughorn is made Potions master. Professor Snape takes up the role of Defence Against the Dark Arts teacher.
As the new term starts Harry comes into possession of a potions textbook with lots of notes written in it, made by someone calling themselves the Half-Blood Prince. The tips help Harry do really well in potions lessons.
There are lots of reports of Death Eaters attacking people, and at one point Ron Weasley is poisoned.
Dumbledore begins special lessons with Harry about Voldemort's past. Harry is told that Lord Voldemort split his soul into seven chunks and hid six of them inside objects, called Horcruxes. The final part is inside Voldemort himself.
Two of the Horcruxes have been destroyed so far, including the diary from The Chamber of Secrets.
Harry and Dumbledore leave to track down another Horcrux, a locket once owned by Salazar Slytherin. In the course of getting it Dumbledore is very badly hurt.
When they return, the Dark Mark is hovering over Hogwarts. A fight is taking place inside the castle between the Death Eaters and Harry's friends and in the course of it Dumbledore is killed by Snape using the Avada Kedavra curse.
While he is escaping Snape reveals to Harry that he is the Half-Blood Prince, and Harry has been using his textbook all year.
When Harry gets to Dumbledore's body he finds the locket, but on opening it discovers that it is a fake and someone else has got there first, leaving a note from someone with the initials RAB.
Harry decides that he will not return to school for his final year, instead saying he will search for, and destroy, the other Horcruxes so that Voldemort can finally be killed.
DADA teacher (and their fate): Finally, it's Professor Severus Snape. He's been after the job for years and has finally got it. As for his fate, well, at the close of the book he seems set to rejoin Lord Voldemort and his Death Eaters.
Best Neville moment: Tough one. Neville doesn't have a huge role in the Half-Blood Prince, but does take part in the battle at the end inside Hogwarts. We also find out that perhaps Neville isn't as hopeless at magic as we thought. He has a new wand in book six and we discover he's been using his dad's until now, which may explain why his spell casting has been so unpredictable in the past.
Last line: His hand closed automatically around the fake Horcrux, but in spite of everything, in spite of the dark and twisting path he saw stretching ahead of himself, in spite of the final meeting with Voldemort he knew must come, whether in a month, in a year, or in ten, he felt his heart lift at the thought that there was still one last golden day of peace left to enjoy with Ron and Hermione.