Now we see the Hogwarts students marching in formation into the Great Hall, where Snape speaks to them.
He tells them the children that Harry was spotted in Hogsmeade—and that if anyone helps Harry, student or teacher, they will be punished. Anyone who fails to report knowing that someone helped Harry is also going to be punished.
So, having said all that, Snape wants to know if anyone has anything to admit or report.
Suddenly Harry steps forward, and the Order appears behind him.
Snape starts to point his wand at Harry, and McGonagall steps in front of him. Then, she uses her wand to scoot Snape out of the hall via the glass window.
Suddenly, we hear Voldemort's voice calling Harry, and then a girl starts screaming and cowering in the corner.
We hear Voldemort's voice speaking to everyone as though through some kind of magical PA system. He demands that the students give him Harry Potter without a fight. They have one hour.
Pansy Parkinson pipes up once the announcement is over and demands that they give Harry over.
After a shocked pause, McGonagall then orders Filch to take all of Slytherin down to the basement. Seems reasonable.
Then McGonagall asks Harry why he's here, and Harry explains he needs time to search for something. McGonagall promises to secure the castle to give him some time.
Harry then goes to look for the Horcrux, and Ron and Hermione go to find something to destroy it.
McGonagall and other professors and members of the Order of the Phoenix cast spells to try to protect the castle from Voldemort.