Harry Potter and the half blood prince movie trailer

As Voldemort and his Death Eaters openly wreak havoc throughout Britain, Minister for Magic Cornelius Fudge has been forced to resign following public outcry over his mishandling the situation. Before he leaves office, he pays a visit to the Muggle Prime Minister of the United Kingdom to warn him that events occurring in the magical world are now having an effect on the Muggle world and that things are going pretty badly for the Ministry of Magic at present. The Prime Minister is then introduced to Fudge's successor, Rufus Scrimgeour. At his home in Spinner's End, Severus Snape is sworn to an Unbreakable Vow by Draco Malfoy's mother Narcissa. Although her sister, Bellatrix Lestrange, distrusts Snape, he agrees to protect Draco during his task assigned by the Dark Lord, and complete the mission should Draco fail.

During the summer, Albus Dumbledore enlists Harry Potter's unwitting help to persuade retired professor Horace Slughorn to return to his old Hogwarts post. When Albus Dumbledore comes to collect Harry, an unsuspecting Harry is told that he has inherited all of Sirius Black's (his deceased godfather) possessions, including the house, Buckbeak, and his mumbling, loyal – to his beloved wailing mistress – house-elf, Kreacher. Harry then spends the remaining holiday at the Burrow with the Weasleys and Hermione. To his family's dismay (especially Mrs. Weasley and Ginny), Bill Weasley has become engaged to Fleur Delacour, the Beauxbatons champion in the Triwizard Tournament. Harry, Ron, and Hermione receive their O.W.L. results. To become Aurors, Harry and Ron must take N.E.W.T.-Level Potions as a prerequisite, but their grades in the subject are too low for Snape's advanced class, thus ending their career ambitions. However, Harry is very pleased (and secretly smug) to discover that he was the only one out of the three of them to get an 'Outstanding' in Defence Against the Dark Arts. While in Diagon Alley, Harry, Ron and Hermione spot Draco Malfoy and follow him. At Borgin & Burkes, a dark magic shop in Knockturn Alley, Malfoy threatens Mr Borgin about repairing one item and keeping another safe. Hermione goes in after to try to find out what he was reserving. Suspecting Draco may be a Death Eater, Harry resolves to keep a close watch on him.

As school begins, Snape is unexpectedly announced as the new Defence Against the Dark Arts instructor while Slughorn replaces him as the Potions teacher. Slughorn only requires a minimum "E" grade (Exceeds Expectations) at O.W.L. to take his N.E.W.T.-level Potion classes, making Harry and Ron eligible for the class. Slughorn lends them old Potions textbooks until they buy their own. Harry's copy is marked on the bottom of the back cover, "This book is the Property of the Half-Blood Prince". The talented former owner's notes help Harry excel in the class (as well as learn a few new spells, some even including the dark arts), but the identity of the "Half-Blood Prince" remains a mystery. As a reward for Harry's performance in Potions, Slughorn gives him a small vial of Felix Felicis, a good luck potion.

Death Eater attacks continue throughout the year and may be linked to events at Hogwarts. On the first Hogsmeade visit, Katie Bell, a Gryffindor student, is seriously injured while carrying a cursed necklace through Hogsmeade, apparently while under the Imperius Curse. In another incident, Ron accidentally drinks poisoned mead intended for Dumbledore. Harry reacts by administering the Bezoar he had submitted previously as an assignment to Slughorn. Hermione is so distraught over this that she and Ron, who were feuding mostly over Ron dating Lavender Brown and Hermione's relationship with Viktor Krum, reconcile; Ron soon breaks it off with Lavender. Meanwhile, Harry realises his true feelings for Ginny, although she is now dating Dean Thomas.

Dumbledore privately tutors Harry using his Pensieve to view collected memories about Voldemort's past. Dumbledore speculates that Voldemort splintered his soul into six fragments called Horcruxes to attain immortality, while leaving a seventh piece in his body. Two Horcruxes have been destroyed (Tom Riddle's diary by Harry^[HP2] and Marvolo Gaunt's ring by Dumbledore).

When Harry finds Malfoy sobbing in Moaning Myrtle's bathroom, they hurl curses at each other. Harry casts "Sectumsempra" inflicting huge gashes across Malfoy's body. Snape arrives and saves Malfoy. He attempts to re-possess the Half-Blood Prince's Potions book, but Harry hands him "Roonil Wazlib's" (a.k.a. Ron's) copy. Harry receives detention, causing him to miss the Quidditch finals. Nonetheless, Gryffindor wins the Cup, and during the victory celebration, Harry's suppressed feelings for Ginny are revealed when he spontaneously kisses her; Ginny has just broken up with Dean Thomas, and she and Harry begin dating.

Harry reports Malfoy's suspicious behaviour to a seemingly unconcerned Dumbledore. He reassures Harry that he trusts Severus in keeping a lookout. Soon after, Harry learns from Professor Trelawney that it was Snape who passed a prophecy to Voldemort that ultimately led to James and Lily Potter's deaths. Enraged, Harry confronts Dumbledore, but he affirms Snape's loyalty. Dumbledore, meanwhile, has located another Horcrux and asks Harry to accompany him in retrieving it. Distrusting Malfoy and Snape, Harry asks Ron, Hermione, Luna Lovegood, Neville Longbottom and Ginny to patrol the halls while he and Dumbledore are gone and gives them the remaining Felix Felicis potion for luck. Harry and Dumbledore apparate to a secret cave. They aim to retrieve the Horcrux (Salazar Slytherin's locket), by advancing past Voldemort's defences. Dumbledore, however, has been greatly weakened due to the mysterious liquid he had to drink in order to acquire the locket.

Returning to Hogsmeade, Harry and Dumbledore see Lord Voldemort's Dark Mark hovering over Hogwarts. They fly to the Astronomy Tower on borrowed broomsticks and are ambushed by Draco Malfoy. Dumbledore paralyses Harry, who is under his Invisibility Cloak, just before Draco disarms Dumbledore. Draco admits he was behind the school attacks and has helped Death Eaters secretly enter Hogwarts via the pair of Vanishing Cabinets, although Dumbledore discerns that Voldemort has coerced the obviously frightened boy.

As members of the Order and the few from the DA battle Voldemort's followers in the castle below, Death Eaters appear in the tower and urge Draco to fulfil his mission—killing Dumbledore—but Draco hesitates. Snape arrives and a weakened Dumbledore entreats him with an ambiguous plea; Snape casts Avada Kedavra which hits Dumbledore squarely in the chest. The impact hurls his body over the tower wall. Upon Dumbledore's death, Harry is released from the paralysing spell. Harry pursues Snape and Malfoy, as their only way of escape would be to disapparate outside the boundaries of Hogwarts. Malfoy escapes as Snape duels Harry. During the duel, Snape reveals that he is the Half-Blood Prince. Though instructive, the duel was ended by Buckbeak's intervention. Snape disapparates and escapes. 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. who has stolen the real Horcrux.

The school year ends abruptly with Dumbledore's funeral. Professor McGonagall is appointed Hogwarts's interim headmistress and Professor Slughorn replaces Snape as the head of Slytherin House. Hogwarts is rumoured to close down due to the murder of Dumbledore. Harry decides to leave school in 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 concludes as Harry looks forward to Bill and Fleur's wedding and being comforted that "...there was still one last golden day of peace left to enjoy with Ron and Hermione."