Half-Blood Prince

Harry Potter and his best friends, Ron Weasley and Hermione Granger, return toHogwarts School of Witchcraft and Wizardry for their sixth year of magical education. Before Returning they find out that Emmeline Vance and Amelia Susan Bones are murdered by Lord Voldemort. It is announced that Severus Snape has become the new Defence Against the Dark Arts instructor, while Horace Slughornhas taken Snape's place as Potions teacher. Harry discovers that the previous owner of his Potions textbook, the "Half-Blood Prince", has annotated the book with refinements that allow Harry to excel in class and become a favourite of Slughorn's. Slughorn is also intrigued by the rumour that Harry is the "Chosen One" who will finally kill the evil Lord Voldemort, who has recently regained power and is set on conquering the wizarding world.

Harry recognises his attraction to Ginny Weasley, but fears that acting on it will harm his friendship with Ron, her overprotective older brother. Ron begins dating Lavender Brown, causing a rift between him and Hermione, who secretly harbours feelings for him. The rift heals only when Ron is nearly killed by poisoned meadintended for Hogwarts' headmaster, Albus Dumbledore. Harry suspects that his nemesis, Draco Malfoy, has become one of Voldemort's supporters and believes he was behind both the mead and a previous failed attack on Dumbledore's life. However, no one seems to believe him.

During private meetings held throughout the year, Dumbledore uses his Pensieve to show Harry memories of Voldemort's past. A memory Harry procures from Slughorn confirms Dumbledore's suspicion that Voldemort splintered his soul into seven fragments in order to achieve near immortality. Six of these fragments are contained in magical objects called Horcruxes, which must be destroyed before Voldemort can be killed. Two Horcruxes have already been destroyed: Tom Riddle's diary, which Harry stabbed with a basilisk fang in his second year, and Voldemort's grandfather's ring, which Dumbledore destroyed during the summer. Dumbledore suspects that the remaining Horcruxes are Voldemort's pet snake Nagini and objects formerly owned by Hogwarts' founders: Salazar Slytherin's locket, Helga Hufflepuff's cup, and an unidentified object of Rowena Ravenclaw's.

After Snape sees Harry cast a curse from the Half-Blood Prince's book and attempts to confiscate the book, Harry hides it in the Room of Requirement. Harry's Hogwarts House, Gryffindor, wins the school's Quidditch championship; euphoric, Harry spontaneously kisses Ginny, and with Ron's diffident approval, they start dating.

Dumbledore locates a Horcrux and asks Harry for help destroying it. They travel to a cave and retrieve what they believe to be Salazar's locket, but Dumbledore is severely weakened after drinking the magical potion that protects the Horcrux. They return to Hogwarts and see Voldemort's symbol hovering over Hogwarts's Astronomy Tower. At the top of the tower, Dumbledore is confronted by Draco. Draco admits that he was behind the attacks on Dumbledore's life, as Voldemort had ordered Draco to kill him and would kill Draco if he failed, but he cannot bring himself to kill Dumbledore on the spot. However, Snape arrives and kills Dumbledore. Enraged, Harry pursues Snape, who fends off Harry's attacks and reveals that he is the Half-Blood Prince shortly before disapparating.

Harry recovers the locket from Dumbledore's body, only to discover that it is a fake left by someone with the initials R. A. B., who stole the real Horcrux and left a note declaring his opposition to Voldemort. The school year ends with Dumbledore's funeral; he and his wand are buried in a tomb beside the lake on Hogwarts' grounds. After the funeral, Harry breaks up with Ginny, fearing that Voldemort will target her if they continue to see each other. He, Ron, and Hermione decide not to return to school the following year, but to hunt for the remaining Horcruxes instead.

[Credit: Wikipedia]