The Half-Blood Prince. This 6th book takes place a few weeks after the end of the 5th book with an invitation to stay with the Weasleys until the start of term. Once at Hogwarts, Harry is confronted with several changes. Snape has his coveted position to teach Defence Against the Dark Arts while there is a new Potions master. Most important of all, with the assistance of the mysterious Half-Blood Prince, Potions is now Harry Potter's best subject.
Private Lessons. Harry learns of Tom Marvolo Riddle's past in his lessons with Hogwart's headmaster. Though puzzled at first by these lessons, Harry can only accept Dumbledore's word that in Voldemort's past lies the key to his defeat.
Death Eaters at Hogwarts. Harry and Dumbledore may have discovered the secret of Voldemort's immortality, but this does not prevent the tragedy at Hogwarts. Mayhem ensues when the Death Eaters attack and when the dust settles, Harry mourns the loss of an old protector.