Harry Potter and the Half-Blood Prince, released on July 16, 2005, is the sixth of seven planned novels in J.K. Rowling's popular Harry Potter series. Set during Harry Potter's sixth year at Hogwarts, the novel explores Lord Voldemort's past, and Harry's preparations for the final battle amidst emerging romantic relationships. In 24 hours, the book sold 6.9 million copies in the United States alone, or 287,564 books per hour, making it the fastest selling book in recent history. It generated over 100 million pounds in sales on its opening weekend, outpacing even the combined take of the top movies at the box office that same weekend. Bookseller Barnes and Noble reported sales averaging 105 copies per second in the first hour of sales. The book is dedicated to Rowling's daughter Mackenzie, who was born in the middle of writing this book.
Voldemort and his Death Eaters openly wreak chaos throughout Britain. Following public outcry over Cornelius Fudge's mishandling of the Voldemort situation, he is fired, and is succeeded by Rufus Scrimgeour as the new Minister for Magic. As a result, Arthur Weasley receives a promotion following the set-up of several new offices. The new windfall greatly improves the family's financial situation.
At his home in Spinner's End, Severus Snape receives a visit from Draco Malfoy's mother Narcissa and her sister, Bellatrix Lestrange. Narcissa swears Snape to an Unbreakable Vow, ensuring he will protect Draco and, should her son fail, complete his mission for the Dark Lord.
Harry spends the Summer at The Burrow with the Weasleys and Hermione (who is also visiting). It is announced that Bill Weasley is engaged to Fleur Delacour, who features in the Goblet of Fire, much to the displeasure of the rest of the Weasleys. Harry, Ron and Hermione recieve their OWL results. They all pass well in most subjects, but due to Snape's requirement of an "O" (Outstanding) at O.W.L., neither Ron or Harry can apply to continue potions at N.E.W.T. level.
As school begins, Snape is announced as the new Defence Against the Dark Arts instructor. With unwitting help from Harry Potter, Albus Dumbledore has persuaded retired teacher Horace Slughorn to resume his old Potions position.
Because Slughorn only requires students to have a minimum "E" grade ("Exceeds Expectations") at OWL to participate in exams for NEWT Potion classes, Harry and Ron are now able to sign up. Slughorn lends Harry an old textbook marked as the property of "The Half-Blood Prince." The talented former owner's handwritten notes help Harry excel in the class, gaining a reputation worthy of Hermione. As a reward, Slughorn gives him a small vial of Felix Felicis, a good luck potion.
Suspecting Malfoy may be a Death Eater, Harry confides his suspicions to Dumbledore, who appears unconcerned, as do Ron and Hermione. Later it is revealed that Dumbledore entrusted Snape to investigate.
Just when Ron and Hermione seem on the verge of a relationship, Ron begins dating Lavender Brown although it is mostly to spite Hermione, who, Ron learned, kissed Viktor Krum. Ron and Hermione continually bicker until Ron is accidentally poisoned. Hermione is so distraught that she and Ron end their feud, and Ron soon breaks up with Lavender.
Dumbledore begins giving Harry private lessons using his Pensieve to view collected memories about Voldemort's past. A memory belonging to Slughorn is partially missing. Aided by the Felix Felicis potion, Harry retrieves the missing portion from him. Dumbledore speculates that Voldemort split his soul into seven parts, storing six pieces in Horcruxes to grant himself immortality, while leaving the seventh in his body. Two Horcruxes have been destroyed (Tom Riddle's diary by Harry[HP2] and Marvolo Gaunt's ring by Dumbledore).
After this time, Harry and Ginny Weasley begin a relationship.
As Harry and Dumbledore leave to find another Horcrux (Salazar Slytherin's locket), Harry leaves the rest of his Felix Felicis to Ron, Hermione and Ginny, for he suspects that Draco Malfoy is up to something again. Giving them swift instructions to patrol the corridors, Harry disapparates with Dumbledore to a secret, hidden cave. Upon retrieving the Horcrux, Dumbledore is seriously weakened. Returning to the castle, they find Lord Voldemort's Dark Mark hovering over Hogwarts. They are ambushed by Draco Malfoy atop the Astronomy Tower. Dumbledore paralyzes Harry, who is hidden under his Invisibility Cloak, just before Draco disarms him. Draco reveals that he helped the Death Eaters enter Hogwarts, although Dumbledore discerns that the obviously frightened boy was coerced into aiding Voldemort's followers.
Death Eaters appear and urge Draco to fulfill his missionkilling Dumbledorebut Draco hesitates. Snape arrives; Dumbledore pleads with Snape, though it is unclear exactly what he is pleading for. Snape, at the end of the plea, kills Dumbledore with the Avada Kedavra killing curse. The force of the spell hurls Dumbledore's body over the tower wall. Upon Dumbledore's death, Harry is freed from the spell Dumbledore placed on him. The Death Eaters flee, and Harry pursues Snape, who identifies himself as the Half-Blood Prince in a short-lived duel before escaping with Malfoy.
Harry recovers the locket from Dumbledore's body only to discover it is a fake. Inside is a note from someone with the initials "R.A.B.". The real Horcrux has been stolen and will be destroyed with the hope that when Voldemort meets his match he "will be mortal once more."
The school year ends abruptly with Dumbledore's funeral. Professor McGonagall is appointed Hogwarts' interim headmistress, although the school may remain closed. Regardless, Harry decides to leave Hogwarts to search for the remaining Horcruxes. Ron and Hermione vow to accompany him, while Harry ends his relationship with Ginny to protect her from Voldemort. The book ends with Harry's heart lifting at the thought that there will be one last golden day with his friends before he has to face the task that lies ahead.
