The Missing Mirror
As soon as Harry, Ron, and Hermione arrive at Hogsmeade, they realize that they have set off some kind of Death Eater alarm. A large group of Death Eaters appears out of nowhere. Luckily, they try to summon the Invisibility Cloak, which cannot be summoned by magic. The Death Eaters are convinced they are in the presence of Harry Potter; therefore, they keep looking for him.
Harry, Ron, and Hermione try to disapparate but are unable to and, unfortunately, they feel the arrival of Dementors. Harry shouts “Expecto Patronum” and out flies his large stag Patronus, which both protects him from the Dementors and alerts all of the Death Eaters to Harry’s whereabouts.
Suddenly “a door opened on the left-hand side of the narrow street, and a rough voice said, ‘Potter, in here, quick!’” Invited into the Hog’s Head and ushered upstairs, the three see a large painting of a blonde girl “who gazed out at the room with a kind of vacant sweetness.”
Downstairs in the Hog's Head, the entire place is full of irate Death Eaters demanding to see Harry Potter. The man at the bar convincingly lies that he set off the alarm and that the Patronus that was seen was a goat Patronus (the man’s own) and not Harry’s. The Death Eaters are suspicious but leave nevertheless.
Upstairs, Harry notices a small mirror underneath the picture of the blonde girl. When the barman returns, Harry also notices that he has bright blue eyes, the same eyes Harry has seen in his own shard of mirror. The man is Aberforth Dumbledore, Albus Dumbledore’s brother.
Aberforth immediately begins an explanation. After Albus Dumbledore explained to his brother what these mirrors could do, the mirrors helped Aberforth keep watch over Harry. They even helped Aberforth see that Dobby had to be sent. The group wonders if the doe Patronus belonged to Aberforth and he assures them that his Patronus is a goat, not a doe.
Aberforth gives the three friends some food and then reveals that he doesn’t have sworn allegiance to Dumbledore. Aberforth believes that Harry should give up his mission and save himself. To do this, Aberforth suggests that they hide with Hagrid in the mountains. Aberforth tells a story to prove his reasoning.
Muggle boys bullied Ariana Dumbledore to the point that she was traumatized and driven insane. Dumbledore (the father) attacked the boys and was given a sentence in Azkaban. This left Aberforth and Albus and Kendra (the mom) to care for Ariana.
Unfortunately, Ariana mistakenly kills Kendra because she was not taught how to control her magical power. With Kendra gone, Aberforth takes care of Ariana while Albus completes his studies at Hogwarts.
Meanwhile, Albus makes friends with Gellert Grindlewald and plans to take off searching for the Deathly Hallows. Ariana gets killed in a duel between the two brothers and Grindlewald. Aberforth thinks that Albus felt free of the family issues at that point, until Harry tells Aberforth that Albus was haunted by a memory when he drank the Inferi poision.
Harry defies Aberforth, saying that sometimes lives must be lost “for the greater good” and that he plans to continue Albus Dumbledore’s mission even if his own life is lost in the process. As Harry tells Aberforth that his mind is made up, Aberforth reveals the way to get into Hogwarts safely: Ariana’s portrait. She disappears into a tunnel behind her: it is the only passageway left unguarded. When Ariana returns, she brings Neville Longbottom with her.