Here is the final installment in our synopsis of Harry Potter and the Half-Blood Prince, the sixth book in the series — your essential cheat-sheet for diving into the seventh and final book, Harry Potter and the Deathly Hallows. See the first five chapters summarized here.
Chapter 26 - The Cave
Dumbledore points out a fissure in the cliff and tells Harry they have to swim. They jump in and swim to a cave. Dumbledore can sense that magic had happened there and starts running his hands over anything he can touch to find an entrance. Dumbledore realizes that blood will open the entrance, the explanation being that one must weaken oneself before entering. Harry insists that he should be the one, but Dumbledore cuts his own arm and the entrance is revealed the moment Dumbledore's blood hits the wall. They enter and find themselves facing a great black lake. They start to walk around it, but Dumbledore warns Harry not to touch the water. Harry wonders how they will get to the Horcrux and suggests a summoning spell. Dumbledore tells him to use the spell and the moment he does something shoots out of the lake and falls back in. Dumbledore suspects the Horcrux is in the middle of the lake, but is not quite sure how to get to it. He starts groping for something in the air and finds what he's looking for. Dumbledore taps his hand and a chain appears. He then taps the chain which starts to coil, pulling a tiny boat into view. Harry wonders what is in the water and Dumbledore says that at some point what is in the water will realize they are not Voldemort. They get in the boat and Harry starts looking in the water and grows concerned as he sees floating bodies. They reach a small island in the middle of the lake and make sure not to touch the water when they exit the boat. There is a basin in the middle of the island that contains some ominous emerald green liquid. Dumbledore concludes that the liquid must be drunk and at the bottom is the Horcrux. He makes Harry promise to make him drink all the liquid which he suspects is there to incapacitate the drinker. Harry very reluctantly agrees and Dumbledore starts drinking. After a couple cups Dumbledore starts to struggle and begs Harry not to make him drink more. However, Harry promised Dumbledore that he would make him drink the potion and so he continues to feed Dumbledore cup after cup of the potion no matter how much Dumbledore protests. Dumbledore starts begging for death and passes out. Harry drops the cup in the basin and tries to revive Dumbledore. Dumbledore asks for water and Harry grabs the goblet barely realizing the locket that is at the bottom of the basin. Harry fills the goblet with his wand, but the water disappears. He becomes desperate and after a few more tries dips the goblet into the lake. The bodies in the lake start to stir and move towards the island. Harry tries to fight them off the Inferi but they start to overcome him. Suddenly a ring of fire appears and the Inferi back off. Dumbledore is on his feet. Maintaining the ring of fire, Dumbledore draws Harry close to him, grabs the locket in the basin, and starts moving towards the boat. The inferi swarm under the boat but they dare not surface and face the fire. Dumbledore is very weak, but Harry helps him out of the cave and tells Dumbledore not to worry and that Harry will get them back.
Chapter 27 - The Lightening-Struck Tower
Harry Apparates them back to Hogsmeade where Dumbledore demands that Harry fetch Snape. Harry is hesitant but agrees and tells Dumbledore to rest while he gets Snape. However, they see the Dark Mark looming over the castle. Madame Rosmerta fetches them two broomsticks. Dumbledore tells Rosmerta to contact the Ministry and tells Harry to put on his invisibility cloak. They fly off to Hogwarts and Harry begins to wonder if his friends are all right. They dismount on the ramparts and Dumbledore tells Harry to summon Snape. Harry is about to go down the stairs but hears someone coming up. Dumbledore tells him to move aside. Just as the door opens, Harry is immobilized underneath his Invisibility Cloak and Dumbledore is disarmed by Malfoy. Dumbledore greets Malfoy who informs him that there are Death Eaters in the school. He commends Malfoy on his clever plan and Malfoy is rather pleased with himself. Dumbledore tells Malfoy to get on with it and kill him, but Malfoy is hesitant and frightened. Dumbledore says he knows that Malfoy in his desperation to kill Dumbledore had almost killed Katie Bell and Ron Weasley with the cursed necklace and poisoned mead. Dumble continues to encourage Malfoy to kill him, but when Malfoy keeps hesitating Dumbledore asks him how the Death Eaters got into the castle. Malfoy says that he used the vanishing cabinet that Montague had gotten lost in last year. He realized that there were a pair of cabinets and one of them was in Borgin and Burke's shop. He was able to fix the broken one and the Death Eaters were able to enter Hogwarts through the vanishing cabinets through the shop. Malfoy says Dumbledore didn't suspect him at the time, but Dumbledore says he did, and had Snape looking over Malfoy. Malfoy says that Snape is a double agent and had been duping Dumbledore this whole time. Dumbledore says he still trusts Snape, but Malfoy says Snape is on the dark side with him, but is somehow trying to steal his glory. Dumbledore also figures out that Malfoy had been controlling Madame Rosmerta with the Imperius curse, which is how Katie got the necklace in the bathroom, and using enchanted coins to give her orders remotely. She also tipped Malfoy off to Dumbledore's absence when he left to look for the Horcrux with Harry. Dumbledore starts discussing Malfoy's options. Malfoy feels like he has no choice but to kill Dumbledore or else Voldemort will kill him and his family. Dumbledore says that he will protect the Malfoys. Malfoy starts to tremble with uncertainty. At this point Amycus, his sister Alecto, and Fenrir Greyback burst in. Malfoy is terrified, but they keep encouraging him to kill Dumbledore. Snape bursts in and pushes Malfoy aside. Dumbledore starts to plead with Snape saying "Severus...please." Snape points his wand at Dumbledore and says "Avada Kedavra." Dumbledore's body flies back into the air and over the battlements. Snape had just killed Dumbledore, with Harry bearing silent witness under his Invisibility Cloak.
Chapter 28 - Flight of the Prince
Snape, Malfoy, and the other Death Eaters leave and Harry finds himself able to move again just as the last Death Eater leaves. Harry runs down the stairs just in time to see Snape shout, "It's over, time to go!" before running off with Malfoy. He sees Ginny, McGonagall, Lupin, Tonks, and others fighting Death Eaters. Harry starts to chase after Snape and Malfoy, shooting curses and hexes at them as they head out of Hogwarts and off the grounds to Disapparate. Snape manages to block everything Harry throws at him while Harry demands that Snape fight back and not be a coward. Someone hits Harry with a curse but Snape screams for everyone to let Potter go because he is for the Dark Lord alone. Harry throws the Sectumsempra curse at Snape, who blocks it and knocks Harry to the ground where Harry loses his wand. Snape tells Harry that he can't use Snape's own spells against him and tells Harry that he is the Half-Blood Prince. Harry demands that Snape kill him then and not be a coward. Snape angrily tells Harry not to call him a coward and slaps Harry with a spell. Harry sees Snape run off and turns to find Hagrid and make sure he all right. Harry finds Hagris and tells him that Dumbledore is dead, but Hagrid won't believe him until they see Dumbledore's body. They walk over to Dumbledore's body and Harry caringly adjusts Dumbledore's glasses and wipes blood from his mouth. Harry find the locket on the ground and notices that it is not the the locket he had see in all those memories. It looks smaller and doesn't have the Slytherin S on it. He opens it up and finds a piece of Parchment in it with a note to the Dark Lord from someone with the initials R.A.B. The note says he has stolen the real Horcrux and will destroy it in the hopes that one day Voldemort will meet his match. Harry does not care who R.A.B. is, only that this Horcrux was a fake and that Dumbledore had sought it in vain.
Chapter 29 - The Phoenix Lament
Ginny brings Harry back into the castle and tells him that Bill Weasley was attacked by Fenrir Greyback. Ginny as tells him that everyone took a bit of the Felix Felicis which helped because none of the Death Eaters were able to hit them. They enter the hospital wing where Professor Flitwick and Neville are resting. Bill is there too and his face is a wreck. Unfortunately, werewolf wounds cannot be healed with potions or spells, and they are not sure what will happen to Bill since Greyback was not fully transformed at the time he attacked Bill. Ginny breaks the news of Dumbledore's death and everyone is devastated, especially Lupin. Harry tells them that Snape did it with the Avada Kedavra curse. Dumbledore's phoenix is flying around outside singing a sad song. Everyone is shocked to hear that Snape killed him, as Dumbledore was so loyal to him. Soon everyone recounts what had transpired: McGonagall sent Flitwick to fetch Snape, and everyone was patrolling the corridors while the Death Eaters entered through the Vanishing Cabinets. Ginny and Neville were keeping watch where the Room of Requirement was located and Malfoy came out with his Hand of Glory (which gives light to its holder) while throwing Peruvian Instant Darkness Powder (purchased at Weasleys' Wizard Wheezes) in the air so it would black out everything. Ron, Ginny, and Neville managed to warn the others and everyone headed towards the Astronomy tower where a fight broke out with the Death Eaters. Flitwick entered Snape's office and immediately afterwards Snape came out and told Hermione and Luna (who were patrolling that area) that Flitwick needed help and had passed out. Snape had probably stunned Flitwick.
As everyone continues to review recent events, Mr. and Mrs. Weasley and Fleur burst in. Mrs. Weasley is devastated and laments that Bill was going to get married. Fleur jumps in and says she will marry Bill no matter what. The two women break down and cry with each other. Tonks suddenly turns to Lupin and says it doesn't matter that Bill was bitten by a werewolf, Bill and Fleur will still marry. Lupin says that it's different and he doesn't want to ruin Tonks life, but Tonks says she loves Lupin and wants to be with him no matter how old, poor, or dangerous he is. McGonagall takes over as interim headmistress and pulls Harry and Hagrid aside. She demands to know where Harry and Dumbledore were that evening, but Harry tells her that he can't say on Dumbledore's orders. It is then decided that the students should have the option to stay for the funeral and that the board of governors should decide if the school stays open or not. Harry leaves the office before the Minister of Magic arrives. Harry goes back to the dorm and Ron asks him if he had found the Horcrux. Harry tells him he did but it's fake and shows Ron the locket. Ron asks who R.A.B. is. Harry doesn't know and doesn't care to know at that moment. He realizes that Fawkes has stopped singing, and in that moment he knows Dumbledore has left the world, and left Harry as well.
Chapter 30 - The White Tomb
All lessons and exams are postponed and Hogsmeade floods with people wanting to attend Dumbledore's funural and pay their final respects. Harry, Ron, Hermione, and Ginny spend all their time together and visit Bill often in the hospital wing. He is recovering but his scarring is very bad. Hermione discovers that Eileen Prince was Snape's mother: she, a pureblood witch, married Tobias Snape who was a Muggle, hence Snape calling himself the Half-Blood Prince. The next day, everyone gathers for Dumbledore's funeral. Many people are in attendance, including members of the Ministry, members of the Order of the Phoenix, Madame Maxine from the Beauxbatons, Tom from the Leaky Cauldron, Cornelius Fudge, Rita Skeeter, Dolores Umbridge, etc. The mer-people and centaurs pay tribute to Dumbledore at his funeral. Eventually Dumbledore's body is encased in a white marble tomb and Harry finally succumbs to the reality of Dumbledore's death. Harry turns to Ginny and sadly says he cannot be with her. His future is uncertain and he does not want to put Ginny in more danger, and she lets him go without a fight, knowing that Harry has to do what he feels he must. Harry gets up and leaves, but on his way out Scrimgeour stops Harry and asks what he and Dumbledore were doing the night Dumbledore was killed. Harry says he has nothing to say to Scrimgeour, and is still Dumbledore's man through and through. Scrimgeour leaves. Hermione and Ron catch up with Harry and ask what Scrimgeour wanted. Harry tells them and also says he won't be returning to Hogwarts next year. He needs to find the rest of the Horcruxes and destroy them. He will go back to the Dursleys', then make a trip to Godric's Hollow (his birthplace and the resting place of his parents) and then head off. Hermione and Ron tell him they will be at his side. Harry starts to protest, but they say they have stuck with him this long and they are not turning back. Harry savors his last peaceful day with Ron and Hermione before the trials ahead.