Conversation so far:
Does Voldemort appear in Harry Potter and the Half-Blood Prince?
Voldemort does not appear in Harry Potter and the Half-Blood Prince.
Was there any flashbacks?
In a series of flashbacks, using the pensieve as a plot device.
Who was the author of Harry Potter and the Half-Blood Prince?
Rowling.
Did Voldemort have to assault anyone?
He murders Amelia Bones of the Department of Magical Law Enforcement.
Did he have to fight any hogwarts?
In the main plot of the book, Voldemort's next step is to engineer an assault on Hogwarts.
Did the hogwarts have a professor?
Hogwarts professor (and re-doubled agent) Severus Snape.

Question: What was the witches name?
Self-contained rewrite: What was the witches name in Harry Potter and the Half-Blood Prince?