Second skirmish at the Cave

The Skirmish of the Horcrux Cave took place in June 1997 after Albus Dumbledore tracked down what he believed to be one of Lord Voldemort's Horcruxes, located in a seaside cave Tom Riddle had visited as a boy while living in Wool's Orphanage.

Tom Riddle's Childhood
As a child, Tom Riddle and some other children were taken by his orphanage to a place nearby the cave for an outing. He took two children, Dennis Bishop and Amy Benson to the cave and terrorised them to the point that the two children were unable to speak of what happened. It is likely he magicked their way down to the cave scaring the other children in the process.

Plot to Kill Albus Dumbledore
Over time Albus Dumbledore came to suspect Voldemort had created Horcruxes. In 1993, he received proof of his theory when Harry Potter described the way in which Tom Riddle's Diary, which was subsequently turned over to him, acted and set off to find and destroy them all. When he found Marvolo Gaunt's Ring in the Gaunt Shack, he realised that one of the Deathly Hallows, the Resurrection Stone, was set in it, and temporarily forgot that the ring was a horcrux. He placed it on his finger hoping to see his sister, father, and mother in order to ask forgiveness for the mistakes of his youth. His hand was cursed horribly, but thanks to his own prodigious skill and Severus Snape's good timing, the curse was stopped for the time being. Dumbledore knew that he would eventually die, and he and Snape set up a plan for Snape to kill Dumbledore. This would accomplish several ends: not harming the soul of Draco Malfoy, who he assumed Voldemort was using to punish the Malfoy family by ordering Draco to kill him, and cancelling the powers of the Elder Wand.



Draco Malfoy's mother and aunt, however, went to see Snape in his home. Narcissa was horribly upset by the task Draco was ordered to do. Bellatrix thought otherwise, saying that her sister should be honoured Draco was given such a task. Snape made Narcissa an Unbreakable Vow, promising that he would help Draco whenever needed, and that if Draco should not succeed, Snape would fulfill the task himself.

Draco thought that if he could fix the Vanishing Cabinet in the Room of Requirement, he could bring Death Eaters into the school. It took him most of the year to do so, and at times he was worried that it would not work. As such, he put Madam Rosmerta under the Imperius Curse. He made her give Katie Bell a cursed Opal necklace, cursing Katie and not getting anywhere close to Dumbledore, and poison mead, for Horace Slughorn to give Dumbledore for a Christmas present. This too did not reach Dumbledore, instead it was consumed by Ron Weasley who would have died if it was not for the quick work of his friend Harry Potter.

Harry and Dumbledore's Lessons
Knowing that he had little time left, Dumbledore began giving Harry Potter private lessons in Harry's sixth year. The object of which was to teach him about Voldemort, his past, his Horcruxes, and his way of thinking, so that once Dumbledore inevitably died, Harry would be able to continue the hunt for Horcruxes and destroy them all. They began the first Saturday after the new term started at Hogwarts. In their first lesson, Harry and Dumbledore viewed Bob Ogden's memory by use of the Pensieve. From this memory, Harry learned of the family roots of Tom Riddle, the Gaunt family on the magical side and Tom Riddle Sr. on the Muggle side. He also learned of the final two heirlooms of the long impoverished Gaunt family, Salazar Slytherin's Locket and Marvolo Gaunt's Ring, the mental instability of Riddle's magical family, and Merope Gaunt's use of a Love Potion to ensnare Tom Riddle Sr.

On a Monday a little over a month later, Harry and Dumbledore had their second lesson. This time they ventured into one of Dumbledore's own memories. While watching the boy, Tom Riddle, as he learned he was a wizard, they gleaned many pieces of information including, his thoughts of death as being a human weakness, his like for gathering trophies, his dislike of having a common name, his enjoyment of solitude and his preference for acting alone most likely stemming from being raised in an orphanage, and his measure of control and intent when using his magic. They discussed the end of Merope Gaunt's life in London and the pawning of the Locket. After the Christmas holidays, the lessons resumed. In their third lesson, Harry and Dumbledore witnessed Tom Riddle discover his heritage and blood status. After the brief memory, they speculated on what happened and came to the same conclusions. Tom Riddle stunned his uncle, stole his wand and used it to murder his muggle relations, the Riddle family. He then replaced the wand, implanted false memories in Morfin Gaunt, and stole Marvolo Gaunt's Ring from him. They also watched the falsified memory of Horace Slughorn, and Harry was assigned to obtain the real one. Before he left, Harry and Dumbledore also talked about Riddle's "friends" which reinforced their idea that he was a loner. Dumbledore's memory, showing Riddle asking Dumbledore for a job as Defence Against the Dark Arts teacher. It is in the final lesson that Harry and Dumbledore decided what the six horcruxes were.
 * Fourth lesson: Hokey the house elf's memory, introducing Hepzibah Smith, Helga Hufflepuff's Cup, and showing once again Salazar Slytherin's Locket.
 * Fifth lesson: Slughorn's real memory of him and Riddle discussing horcruxes

Finding the Locket Horcrux
Setting off from Hogwarts in the evening, he and Harry Potter Apparated to just outside the cave, being unable to enter directly due to its protective enchantments. Once inside, Dumbledore located the Horcrux's second line of defence; a hidden doorway which only opened when it received an offering of blood. They next found themselves in a vast chamber containing an underground lake, with a solitary island at its centre from which a faint green light was visible. After a failed attempt by Harry at Summoning the Horcrux, Dumbledore located a carefully concealed boat that would allow them safe passage across the lake. During the crossing, Harry learned of the Horcrux's third line of defence; the lake was filled with Inferi, which would attack anyone who touched the lake's water. Dumbledore instructed Harry on the use of fire as the weapon of choice against the Inferi, should it become necessary.

Arriving at the small island, they found a basin filled with glowing green potion. This last defence could not be removed by Vanishing or being scooped out; someone would have to drink it to get to the Horcrux that lay within. Dumbledore ordered Harry to help him drink all of the potion, no matter what effects it caused, even if Harry had to force it down Dumbledore's throat. While he drank it, he had visions of the duel between him, his brother Aberforth, and the Dark Wizard Gellert Grindelwald that led to his sister Ariana's death. When they finally got the locket, Harry attempted to summon water for Dumbledore with an Aguamenti charm, but this proved ineffective as the water disappeared before Dumbledore could drink it. In desperation, Harry filled a cup with water from the lake. After Dumbledore drank it, the Inferi climbed up from the lake and attempted to kill them. Harry panicked and attempted to fight back with a multitude of spells and curses, including Impedimenta and Sectumsempra, but none of them worked since the Inferi were too numerous and did not feel pain. Dumbledore, having regained consciousness, created a ring of fire around them that repelled the Inferi, driving them back into the lake while he and Harry escaped in the boat.



Harry used a small cut on his arm to reopen the hidden doorway, and once outside the cave they Disapparated back to Hogsmeade.

Return to Hogwarts and Battle of the Astronomy Tower
Madam Rosmerta alerted Dumbledore that the Dark Mark was hovering over Hogwarts. She leant Dumbledore and Harry two broomsticks, and they flew back to Hogwarts, Dumbledore lifting the protective enchantments casted over Hogwarts so that they could enter. Harry wanted to go get Poppy Pomfrey, but Dumbledore asked specifically for Snape.

Draco had finally fixed the Vanishing Cabinet and let Death Eaters into the school. The Dark Mark was not placed there because they had killed someone; it was a trick so that Dumbledore would come back faster. However, Death Eater Gibbon was killed accidentally by Thorfinn Rowle. Bill Weasley was also brutally attacked by Fenrir Greyback, even though it was a not full moon. Because of this, Bill would not ever be a full warewolf, but have a tendency to enjoy raw meat.

Dumbledore put a Full Body-Bind Curse on Harry, who had his Invisibilty Cloak on. Draco disarmed Dumbledore, but did nothing else but talk between themselves, discussing how Draco had almost killed two other innocent students. Other Death Eaters soon joined Draco in the tower, but nobody did anything, as it was Voldemort's order for only Draco to kill Dumbledore. Snape soon joined them, and killed Dumbledore.

Aftermath
Dumbledore was put to rest at Hogwarts, with every student and professor from Hogwarts attending, as well as many other people from the Ministry of Magic and the wizarding world.

After Dumbledore's tragic death, Harry noticed that the locket they had obtained from the cave was not Salazar Slytherin's. The "Horcrux" was a fake. Finding a cryptic note inside from an "R.A.B.", Harry kept the locket, not because it was valuable, but because of what it had cost to obtain it.

Appearances

 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows