In the sixth year at Hogwarts School of Witchcraft, and in both wizard and muggle worlds Lord Voldemort and his henchmen are increasingly active. With vacancies to fill at Hogwarts, Professor Dumbledore persuades Horace Slughorn, back from retirement to become the potions teacher, while Professor Snape receives long awaited news. Harry Potter, together with Dumbledore, must face treacherous tasks to defeat his evil nemesis.