JK Rowling also told us that there will be two key questions about the plot of the book.

"She did not give much away about book six, which will be called Harry Potter and the Half-Blood Prince, but she said a lot of questions will be answered in it.

She also revealed there were two key questions about the whole plot that she had never been asked.

The first is Why didn't Voldemort die when he tried to kill Harry? JK said that in the end of book four, Voldemort had said he had taken various steps against dying, but we should be wondering exactly what he did.

The second question is Why didn't Dumbledore try to kill Voldemort in that scene at the end of book five?

Dumbledore gave a kind of reason to Voldemort but it's not the real answer, and that Dumbledore knows something more.

JK said if we are wondering about the overall plot, we should be concentrating on those two questions."