The Minister of Magic visits the Muggle Prime Minister to inform him that Voldemort is back and wreaking havoc on the wizarding world and the Muggle world.
Meanwhile, Bellatrix and Narcissa visit Snape, imploring the professor to help Draco. Voldemort has given Draco an assignment and Narcissa is worried. Snape makes an Unbreakable Vow to watch over Draco and carry out Voldemort’s orders if Draco fails.
At the Weasleys, Harry arrives and learns that Bill and Fleur Delacour are engaged. Harry, Hermione, and Ron receive their O.W.L. (Ordinary Wizarding Levels) test scores. Harry failed Divination and History of Magic, but did well in everything else.
Harry receives news that he is the new Quidditch Captain. The friends head to Diagon Alley, which is more empty than usual because people are afraid. They go to Fred and George’s joke shop, which is thriving despite the depression in Diagon Alley. Harry spots Draco Malfoy outside, and follows Draco to Borgin and Burkes, a store that sells Dark Arts objects. Draco asks the proprietor to keep something for him and repair it.
Afterward, Harry sneaks into Slytherin’s train compartment to spy on Draco, and hears Draco bragging about moving on to better things. As everyone disembarks, Draco catches Harry, paralyzing him with magic, breaks Harry’s nose, and throws the invisibility cloak over him and leaves him there.
Luckily, Tonks discovers and frees him. She is stationed near the school as security. At the gate, Snape walks him back to the school, berating him for his tardiness.
Dumbledore announces a new Potions teacher, Horace Slughorn. To everyone’s shock, Snape has been appointed the Defense Against the Dark Arts teacher.
In Potions, Slughorn has them mix up a “Draught of the Living Death.” Harry makes the best potion by following handwritten directions in his textbook, and wins a luck potion. He finds “This book is property of the Half-Blood Prince” written in the book.
Harry starts private lessons with Dumbledore. At his first lesson, they use the Pensieve to visit memories that will help Harry survive. They witness Voldemort’s mother, Merope, who was part of a violent, unstable wizarding family, the Gaunts. Merope uses a love potion to marry Tom Riddle, Sr., later bearing his child. However, Tom leaves her and the child when the potion wears off.
Harry holds Quidditch tryouts. Ron narrowly wins Keeper position over a boy named Cormac McLaggen, who is angry he has not made the team.
During a trip into Hogsmeade, the friends witness Katie Bell become cursed from handling a Dark necklace from Borgin and Burkes. Her friend says she was going to deliver it to someone at Hogwarts.
At Harry's next lesson with Dumbledore, they look at a memory of young Tom Riddle. Tom has strong powers and uses them to hurt others. Even as a child, Tom had already begun to become Voldemort.
At the first Quidditch match, Ron is nervous so Harry makes him believe he has slipped him the luck potion. Gryffindor wins! Afterwards, Ron kisses Lavender Brown and Hermione becomes jealous. Harry realizes that he has feelings for Ginny.
At Slughorn’s party, Harry is accosted by Slughorn, who wants an author friend of his to write Harry’s biography. Malfoy crashes the party and Snape is angry. Harry overhears Snapeoffering to help Draco with his. Harry learns that Snape has made an Unbreakable Vow to protect Draco.
At Harry’s next lesson with Dumbledore, they enter the memory of a teenage Tom. Tom visits his Gaunt relatives and discovers his parentage. He steals his uncle Morphin’s wand and kills Tom Riddle, Sr., and erases Morphin’s memory. Morphin dies in Azkaban...
(This entire section contains 1194 words.)
for the crime. They also look at a memory in which Tom asks Slughorn about Horcruxes. Slughorn has tampered with the memory and his answer has been erased. Dumbledore tells Harry it is his mission to recover the truth.
Harry asks Slughorn about Horcruxes and Slughorn becomes upset, avoiding Harry. At Apparition lessons, Harry overhears Malfoy ask Crabbe and Goyle to be his lookouts. Harry begins to keep an eye on Draco, but at times he seems to disappear from Harry’s map.
Ron accidentally ingests a love potion that was meant for Harry. Slughorn provides an antidote, and they toast with mead that Slughorn was meaning to give to Dumbledore. Ron drinks it before the others, and collapses to the floor. Harry throws an antidote down his throat.
In the dorm, McLaggen offers to take the recovering Ron’s place on the Quidditch team, but he messes up and they lose the match. Harry cracks his skull, and while incapacitated, asks the house elves, Kreacher and Dobby, to spy on Malfoy.
During Harry’s next lesson, he learns that Voldemort got a job at Borgin and Burkes after graduating, and wanted to teach at Hogwarts but Dumbledore would not hire him.
Harry discovers that Malfoy is using the Room of Requirement. Harry realizes he can use his luck potion to recover Slughorn’s memory. Harry takes the potion and runs into Slughorn at Hagrid’s. The teachers get drunk and Slughorn divulges the memory. A Horcrux is an object in which a person has hidden part of their soul. Dumbledore believes that Voldemort has hidden his soul in many Horcruxes in an attempt to achieve immortality.
Everyone is gearing up for the Quidditch match, but Harry is distracted by his crush on Ginny. He runs into Draco and they hex each other; Harry uses a hex from his Potions textbook. It is Dark Magic, and Snape punishes him by keeping him from the Quidditch match. However, Gryffindor wins, and Harry kisses Ginny in his excitement.
Harry goes to see Dumbledore when he encounters Trelawney. She tells him the story of the day that she prophesized about Harry and Voldemort, and mentions that Snape overheard. Harry realizes that Snape informed Voldemort, thus leading to Harry’s parent’s deaths. In Dumbledore’s office, Dumbledore wants Harry to accompany him to one of the Horcruxes.
Harry and Dumbledore go to a cave, where they must overcome several obstacles to reach an island at the center of a lake. There is a basin with a potion, and Dumbledore drinks the potion to get the Horcrux. Harry revives him with water, but Inferi (dead people) attack and Dumbledore defeats them with fire.
Back at Hogwarts, the Death Eaters have attacked. Malfoy has let them in through a Vanishing Cabinet in the Room of Requirement. Snape kills Dumbledore. Harry chases after the Death Eaters, shouting hexes, and Snape mocks Harry for using his hexes: Snape is the Half-Blood Prince! Harry returns to the castle to find everyone around Dumbledore’s body. The Horcrux has fallen out of his pocket. Inside there is a note which reads, “I have stolen the real Horcrux and intend to destroy it." Harry is devastated. There are no more fatalities, but Bill has been bitten by a werewolf and is wounded.
At Dumbledore’s funeral, an unprecedented crowd pays their respects. Harry resolves to find and destroy the rest of the Horcruxes, thus destroying Voldemort.