Attack at the Black Lake

The attack at the Black Lake took place on 6 June, 1994 when over one hundred Dementors attacked Harry Potter, Hermione Granger, and Sirius Black at the said lake in 1994. Harry attempted to defend them with a Patronus Charm, but failed due to the sheer amount of Dementors. However, he and the others were saved by his future self, who had travelled back in time using Hermione's Time-Turner. Catching a brief glimpse of their saviour, Harry initially mistook the mysterious figure for his father.

Harry awoke in the hospital wing, and with Hermione, he tried to convince Cornelius Fudge, Severus Snape, Poppy Pomfrey, and Albus Dumbledore that Sirius was innocent. Of them, only Dumbledore believed this. The Headmaster, then, discreetly told them to go back in time, and that they would be able to save more than one innocent life. Leaving Ron, who was injured, the two ventured three hours back in time.

Background information
"He's at Hogwarts..."

- Sirius Black talking about Peter Pettigrew in summer of 1993

Since the autumn of 1981, Sirius Black had been the most notorious prisoner in Azkaban. He had been wrongfully imprisoned for betraying James and Lily Potter and the murder of Pettigrew and twelve Muggles. He was also thought to be both a loyal supporter of Lord Voldemort and certifiably insane. Both of these assumptions were incorrect as well. Twelve years after his incarceration, Minister for Magic Cornelius Fudge made a routine visit to the prison. When he passed Black's cell, Sirius asked the Minister for his newspaper remarking that he missed doing the crossword puzzles. In the newspaper, Sirius saw a picture of the Weasley family. He also saw another familiar sight in that picture. In it was Ron's rat Scabbers, but Sirius could tell that the rat was in fact Pettigrew in Animagus form.

Upon seeing that picture, he realised that Pettigrew was perfectly placed to attack Harry should the Dark Lord return. Consumed with the idea of saving Harry from Pettigrew, Sirius planned to escape from Azkaban. The Dementors noticed that he began muttering "He's at Hogwarts" in his sleep. One day during the summer of 1993, when the guards opened the door to his cell to bring his food, Sirius slipped past them in his Animagus form. Upon escaping, he set off for Hogwarts and Pettigrew.

Consequences of escape
Immediately, the Ministry of Magic began the arduous task of tracking Black down. The Dementors were tasked with searching the countryside, while Fudge informed the Muggle Prime Minister. The Ministry published thousands of "Wanted" posters bearing Sirius' likeness. The entire populace was on edge, for they thought Sirius to be a maniac. In the climate of fear, the Ministry thought it best not to inform the public of the truth with regards to any progress. They continued to say that they were close to finding Black, when according to Arthur Weasley, they had made no visible progress.

On 1 September, the Hogwarts Express was searched by Dementors. This had a disconcerting effect on many of the students. Harry, for example, collapsed in their presence when they searched his compartment. That evening at the Welcoming Feast, Dumbledore informed the students that Dementors would be guarding the castle's grounds and entrances. Hundreds of Dementors were positioned around the school and in Hogsmeade village. The village itself was searched many times. Even with this strengthened security, however, Sirius managed to gain access to the castle at least twice.

Background
On 6 June, Harry, Hermione and Ron left the castle just before sunset for Rubeus Hagrid's cabin. At dusk, his hippogriff Buckbeak was to be executed for an attack upon Draco Malfoy. The students knew that Buckbeak meant very much to Hagrid, and they ventured out of the castle to console him. While at Hagrid's, Hermione found Scabbers, Ron's rat, who they assumed to be dead. After leaving hurriedly, Scabbers bit Ron and ran away. They chased him to the shadow of the Whomping Willow, where Sirius in his Animagus form dragged Ron and Scabbers into a tunnel underneath the tree. With the aid of Hermione's cat Crookshanks, Harry and Hermione pursued Ron through the tunnel. Upon reaching its end, they emerged in the Shrieking Shack. There, they found Ron but were ambushed by Sirius who had transformed back into human form. After Professor Lupin and Professor Snape, arrived, and the latter was knocked out, Scabbers was revealed to be Pettigrew. The whole story of Sirius's past came to light, and Harry came to believe that his godfather was innocent. He would not, however, permit his father's best friends to become murderers. He believed that Pettigrew should be handed over to the Dementors. With that in mind, the assembled group set out for Hogwarts.

Attack
"With a patronus? I heard Snape telling Dumbledore. According to him, only a really powerful wizard could've conjured it."

- Hermione Granger regarding Harry's Patronus

When the group emerged from the tunnel beneath the Whomping Willow, they set off across the grounds. That evening was a full moon, and when the moon came out from behind a cloud, Lupin transformed into a Werewolf. To protect Harry, Ron, and Hermione from harm, Sirius transformed into his Animagus form and fought with Lupin. He was badly injured in the fight, and Lupin ran into the forest. During Lupin's werewolf transformation, Pettigrew managed to remove himself from his restraints. He sprung for Lupin's wand, with which he stunned Ron and then transformed into his Animagus form and escaped. While Ron was incapacitated, Harry and Hermione ran in search of Sirius to the shores of the Black Lake. They found him on all fours with an army of Dementors bearing down upon him. Harry told Hermione to think of something happy, and they both tried to conjure a Patronus. Hermione could not summon anything at all and soon passed out; Sirius passed out, as well. Harry had managed to produce a wispy shield, but he could not drive away the hundred Dementors.

Believing that Harry was a threat, the Dementors closed on him. Once he could no longer produce a Patronus, Dementors attacked. One Dementor brought Harry's face up to an unhooded Dementor's for the Dementor's Kiss, Meanwhile, Sirius was Kissed and his soul was pulled out his mouth, but wasn't ingested by any dementors. When all hope was lost and as the Dementor was going to Kiss Harry, a bright light shone out from across the lake. A blindingly white stag charged across the lake, and drove away the Dementors. As Harry was about to pass out, he saw a familiar figure welcoming the stag back across the lake. For a fleeting moment he believed it to be his father.

Some time after the Dementors had been driven away, Sirius was taken to and locked in Filius Flitwick's office and Harry, Ron and Hermione were taken to the Hogwarts Hospital wing. There, Fudge and Snape discussed the implications of Sirius' capture, while Harry and Hermione tried to persuade them of his innocence. This was unsuccessful, as Snape had told Fudge that Sirius Confunded the pair, and therefore their assertions were considered null. Dumbledore then arrived and announced he had spoken to Sirius and needed to talk to Harry and Hermione in private. After Fudge, Snape and Madam Pomfrey left the wing, Harry and Hermione tried to persuade Dumbledore that Sirius was innocent, not knowing they in fact shared the same view. Dumbledore told the pair subtley to travel back in time three hours using Hermione's Time-Turner, which she had been given to be able to cope with attempting twelve O.W.Ls. Upon travelling back in time and hiding from their past selves, Harry and Hermione sprinted towards Hagrid's cabin, where they attempted to save Buckbeak, whom they worked out was one of the 'innocent lives' that Dumbledore hinted at in the hosptal wing. This turned out to be difficult, as they had to do this in the sixty second time window between the execution party entering and exiting the cabin, and also Buckbeak's reluctance to leave Hagrid. Nevertheless, they managed to lead Buckbeak into the forest. Dumbledore may have been deliberately stalling inside the cabin with the knowledge that he would send Harry and Hermione (and presumably Ron) into the past in the future, as he said 'How extraordinary' with a "note of amusement in his voice".

After rescuing Buckbeak, the pair went the Whomping Willow where they watched Lupin and Snape enter the tree, and Hagrid making his way to the castle. Despite Harry's impatience and desire to intervene, they waited for the group to emerge from the tree after the incident in the Shrieking Shack. Upon realising that they would cross paths with Lupin in Werewolf form, they ran back to Hagrid's cabin and waited there.

After a short time, Harry realised it would be hard to tell when to leave, so we left then, alone. After arriving at the lake, he saw the Dementors emerge "out of the darkness from every direction". They then headed for the opposite bank, for Harry and Hermione's past selves and Sirius. Harry ran to the spot where he saw the mysterious figure and waited. After watching the Dementor in the process of Kissing, he realised he had actually seen himself casting his Patronus. He stepped out from the bush he was behind and shouted the incantation. He produced an blinding, dazzling stag which charged at the Dementor, saving himself, Hermione and Sirius from the Kiss.

Aftermath
"You think the dead we have loved ever truly leave us? You think that we don't recall them more clearly than ever in times of great trouble?"

- Albus Dumbledore

The Harry and Hermione that had gone back in time then waited until they saw the executioner, Walden Macnair, leave the castle. Then they flew Buckbeak per Dumbledore's instructions up to Flitwick's office. They rescued Sirius and gave him Buckbeak on which to escape. The pair then retreated to the hospital wing before they created a paradox in time. The Dementors were removed from Hogwarts and Sirius Black lived in secret for another two years, the last year of his life back in his house along with Buckbeak. He was killed by Bellatrix Lestrange in the Battle of the Department of Mysteries, although after that he was exonerated posthumously, Harry was again attacked a year later and was almost expelled.

Pettigrew lived for another four years, becoming one of Lord Voldemort's servants. However, due to Harry not letting Sirius Black and Remus Lupin kill him, he owed Harry a life debt. During the Skirmish at Malfoy Manor, Wormtail was killed by his own silver hand after he hesitated in killing Harry.

Behind the scenes

 * In the film adaptation of Harry Potter and the Prisoner of Azkaban, the lake where the attack takes place appears to be a separate one to the Black Lake, which is the attack's location in the book. The Black Lake appears with a completely separate appearance to this lake earlier in the film, appearing exactly as it does in the previous two film adaptations and the following three. It is therefore unlikely that both lakes are intended to be the same by the filmmakers.
 * Also, in the film adaptation, Hermione does not appear in the scene.

Appearances

 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Prisoner of Azkaban (film)
 * Harry Potter and the Prisoner of Azkaban (video game)
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * LEGO Harry Potter: Years 1-4
 * Pottermore