Harry Potter and the Half-Blood Prince

In the previous book, Harry Potter and the Order of the Phoenix, the last chapter, titled 'The Second War Begins,' started:

'In a brief statement on Friday night, Minister for Magic Cornelius Fudge confirmed that He Who Must Not Be Named has returned to this country and is once more active.

'It is with great regret that I must confirm that the wizard styling himself Lord – well, you know who I mean – is alive and among us again,' said Fudge.'

Harry Potter and the Half-Blood Prince takes up the story of Harry Potter's sixth year at Hogwarts School of Witchcraft and Wizardry at this point as Voldemort's power and followers are increasing day by day, in the midst of this battle of good and evil.