July. Britain lay dark under the shadow of the evil Voldemort’s return. The Minister of Magic made one of his rare calls
on the Prime Minister (of Muggles) to assess him of the situation. Some distance away, Death-Eater (Voldemort supporter) sisters Narcissa Malfoy and Bellatrix Lestrange visited Hogwart’s defence against the dark arts teacher Severus Snape’s house where Snape, to Lestrange’s astonishment, made a magic oath to protect Narcissa’s son Draco should a certain secret task Voldemort had given him go awry.
Meanwhile. Harry, saddened by his Godfather Sirius’ recent death in the battle at the Ministry of Magic, waited for Hogwarts School of Witchcraft and Wizardry Headmaster Dumbledore to collect him from his Uncle Vernon’s house in Surry and take him to spend the rest of the summer with his friend Ron Weasley at the Burrow in Ottery St Catchpole until they all returned to Hogwarts for the fall term, half believing Dumbledore wouldn’t come. Dumbledore came, had Harry pack and then took him to a ransacked house where they found the elusive, effusive, corpulent, and charmingly self indulgent wizard, Horace Slughorn, the retired former potions master at Hogwarts. Dumbledore used Harry’s notoriety and cache and Slughorn’s obsession with and skill at discovering exceptional people and networking them to entice him to return to Hogwarts. Dumbledore then enigmatically told Harry he, Dumbledore, would be giving Harry private lessons.
Dumbledore then took Harry to Ron’s where Harry, in addition to spending one of his most pleasant summers yet, was immediately embroiled in the controversy surrounding the wedding of French Veela Witch, Fleur, to Ron’s older brother Bill (The Weasleys preferred Nymphadora Tonks). Summer passed and they all went to London to the increasingly beleaguered looking Diagon Ally to purchase school supplies. Harry, under his invisibility cloak, saw Draco Malfoy in Borgin and Burkes dark magic shop doing something suspicious leading Harry to think Draco was plotting something.
On the Hogwarts Express, Harry met Slughorn who had already begun to bring his favourite students together (including, surprisingly, Ginny Weasley) and then wearing the invisibility cloak tried to overhear what Draco was telling his friends. Draco found him, put a petrifying hex on him, punched his nose and left him under the invisibility cloak assuming, undiscovered, the train would take him back to London. Harry was rescued in time by Tonks.
Back at school, Harry was captain of the Gryffindor Quiddich team and Ron and Hermione again prefects. Harry was obsessed by the idea Draco planned something evil. Harry soon found that Dumbledore’s lessons consisted of visiting in the pensieve old memories Dumbledore had collected of Voldemort’s mother and father, Voldemort’s birth, certain family heirlooms and Voldemort’s formative years at an orphanage, Hogwarts and his job at Borgin and Burkes. Dumbledore showed Harry a memory of professor Slughorn where Slughorn refused to tell Tom Riddle (young Voldemort) anything about Horcruxes. Dumbledore told Harry the memory had been altered and Harry must somehow charm the true memory from Slughorn.
Harry lacked a book in potions and Slughorn gave him an old one from the cabinet with spells and notes handwritten in the margins. Using these notes, Harry quickly excelled in potions and won a bottle of Felix Felicis – a one-day good-luck potion reward for the best potion. The book also taught Harry some powerful hexes.
Harry spent his year spying on Draco, maintaining the shaky dominance of the Gryffindor Quiddich team and becoming increasingly fond of Ron’s sister Ginny. Ron and Hermione quarrelled, and Ron, jealous, entered a steamy relationship with Lavender Brown (of whose clinging attentions he soon tired). Giant spider Aragog died and Harry, drinking part of the felix felicis, used the opportunity to help Slughorn gain some invaluable venom from Aragog’s fangs. Ingratiated and more than a little drunk (Aragog’s funeral), Slughorn gave Harry the memory where he explained how to divide one’s soul into parts for inclusion in horcruxes. Doing so had made Voldemort well nigh immortal. Harry fought Draco and used a potent secumsempra curse from his potions book. Snape, healing Draco, realized Harry had his old potions book with his handwritten notes, but Harry hid it in the room of requirements rather than surrender it. Harry at last realized he loved Ginny and they became a couple. Ron and Hermione reunited.
Dumbledore took Harry on his last lesson– to a seaside cave where Voldemort had hidden a horcrux in a basin full of poisonous potion on an island in an inferi (zombie) infested lake. Dumbledore had Harry make him drink the potion, take the locket, and return them to the castle where they found Draco raising Voldemort’s mark and letting death eaters into the castle. Draco confronted Dumbledore but could not kill him (Harry watched from under the invisibility cloak). Snape ran to where they were, killed Dumbledore with a killing curse, took Malfoy and tried to flee with the Death Eaters. Harry chased and fought him, but Snape was too strong and, with Malfoy and the death eaters, escaped. In the battle, all of Harry’s friends (Dumbledore’s Army) had helped teachers and some Order of the Phoenix members fight the Death Eaters. Bill Weasley’s face was maimed but Fleur insisted she would love him anyway which endeared her at last to the Weasleys. Harry, Ron and Hermione agreed at Dumbledore’s funeral not to attend Hogwarts next year but to finish the destruction of Voldemort’s Horcruxes.