Chapter Thirty-one, The battle of Hogwarts Summary

Once all the houses have been gathered, the voice of Voldemort is heard. He says that they have until midnight to give up Harry before he begins killing them. This gives them about a half hour. Someone from Voldemort's old house, Slytherin, is ready to give him up. They make her leave first. All the Slytherins join her. Some of the Ravenclaws and Hufflepuffs stay, and about half of the Gryffindors, who are from Harry's house, and who are noted for bravery.

The battle begins, although Voldemort does not enter the battle himself. He sends his supporters to fight. Since no human still alive has seen the diadem, Harry goes and talks to the ghost of Ravenclaw tower. She tells him that she stole the diadem from her mother a long time ago...