Spontaneous assembly at the Great Hall

"Many of you are surely wondering why I have summoned you at this hour. It's came to my attention that earlier this evening Harry Potter was sighted in Hogsmeade. Now... should anyone, student or staff, attempt to aid Mr. Potter, they will be punished in a manner consistent with the severity of their transgression. Furthermore, any person found to have knowledge of these events, who fails to come forward, will be treated as equally guilty. No one?"

- Severus Snape to the students and staff.

Headmaster Severus Snape summoned all students and staff to a spontaneous assembly after Harry Potter, Ronald Weasley and Hermione Granger were sighted in Hogsmeade on 1 May, 1998. During the meeting, all attendees were warned that any attempt to aid Harry Potter into the Castle would result in serious punishment. After both student and staff were threatened with severe punishment if they did not come forward with any information regarding Harry Potter's movements, the meeting was interrupted by Harry and the members of the Order of the Phoenix's arrival, thus setting the stage for the duel between Snape and Professor McGonagall.

Background
After Harry Potter, Ronald Weasley and Hermione Granger broke into Gringotts Wizarding Bank and stole Helga Hufflepuff's Cup, one of Voldemort's Horcruxes, Voldemort became aware that the trio was hunting down and destroying his Horcruxes. Harry had a vision of Voldemort, in which he saw the Dark Lord threatened and angry, and they realised Voldemort would make sure they would not find the rest. Learning from one of his visions that one of the remaining Horcruxes was something to do with Castle and Rowena Ravenclaw, Harry, Ron and Hermione Apparated to Hogsmeade, from where they thought they could proceed to the Castle. However, once there, a Caterwauling Charm made their presence known to the Death Eaters, and they retreated into the Hog's Head Pub where Aberforth Dumbledore, the barman, hid them. After a brief exchange with Aberforth, the three left for Hogwarts via a secret passage behind the portrait of Ariana Dumbledore. They were received by Neville Longbottom, who took them to the Room of Requirement, where the Dumbledore's Army members were hiding from Amycus and Alecto Carrow, the Death Eaters in charge of all violent punishment. While they all welcomed Harry, Ron and Hermione, Ginny Weasley came into the room with news that Snape had heard that they had been sighted at Hogsmeade, and was summoning an assembly in the Great Hall.

The assembly


The students marched down the Grand Staircase in formation, under the watchful eye of Amycus Carrow on a overhead balustrade. The students stood assembled in the Great Hall, the teachers standing by them, as Snape, flanked by Amycus and Alecto, rose to the raised wooden platform on the Hall. Snape started his speech by saying that any attempt to aid Potter would result in punishment in a manner consistent with the severity of their transgression. As both students and teachers shifted nervously at the threat, Snape slowly crossed the aisle of the Hall saying that any person found to have knowledge of Potter's movements, who failed to come forward, would be equally severely punished.

Not wanting anyone to be punished for him, Harry shockingly revealed himself, hidden in student garb, among the Gryffindor students. Members of the Order of the Phoenix, led by Kingsley Shacklebolt promptly stepped into the Hall. Both Amycus, Alecto and Severus Snape pointed their wands at Harry. Professor McGonagall pushed Harry aside, and took his place as most of the teachers pointed their wands at Snape. McGonagall and Snape then engaged in duelling before the whole school, which resulted in the flight of Snape and the defeat of the Carrows.

Aftermath
"COWARD!"

- Minerva McGonagall yells after Snape flies out of the Castle.

After Snape fled, Voldemort, with a magically amplified voice, made an ultimatum to the school: or they would bring him Harry Potter, or none of them would be spared and the Death Eaters would attack the Castle. McGonagall encharged Argus Filch with the evacuation of students (and the imprisonment of Slytherin students in the dungeons), while the Hogwarts defenders started organising themselves for battle, and building up magical defenses.

Appearances

 * Harry Potter and the Deathly Hallows: Part 2
 * Harry Potter and the Deathly Hallows: Part 2 (video game)