DH31: The Battle of Hogwarts – Harry Potter Lexicon

"IF WE DIE FOR THEM, I'LL KILL YOU, HARRY!"
-- Ron Weasley

Professor McGonagall orders the evacuation of those underage or who do not wish to fight. Lord Voldemort delivers an ultimatum. Harry is told how Voldemort acquired the diadem of Ravenclaw by the Grey Lady, Ravenclaw’s ghost. She reveals that she is Helena Ravenclaw, Rowena’s daughter, and that Helena stole the diadem from her mother. After hiding the diadem in Albania, she was murdered by the Bloody Baron. She confesses to Harry that she told a young Tom Riddle her story and where to find the diadem. Ron and Hermione destroy Hufflepuff’s cup using a basilisk fang taken from the Chamber of Secrets and together they go to the Room of Requirement to destroy the diadem. There they encounter Draco Malfoy, Crabbe, and Goyle, but Draco’s former henchmen no longer answer to him; during the subsequent duel, Crabbe unleashes Fiendfyre, which destroys much of the room’s contents and kills him. Harry, Ron and Hermione escape, rescuing Draco and Goyle in the process. They then encounter Percy and Fred Weasley, duelling Death Eaters, only to be caught by an explosion that kills Fred.

Calendar and Dates

Immediately after the preceding chapter's action, so still later on the same night in May, 1998.

Interesting facts and notes

We've only got half an hour until midnight

So it is 11:30 p.m. Harry, Ron, and Hermione got up at dawn for the raid on Gringotts, so they've had a very long day already.

the three highest Towers - Ravenclaw, Astronomy, and Gryffindor

We know from that the entrance to Ravenclaw Tower is on at least the sixth floor, since it is at the top of a staircase beginning on the fifth floor (DH29), but we don't know how many floors are spanned by the staircase, so we aren't sure whether the entrance to Ravenclaw Tower is on the sixth floor or on the seventh floor. Gryffindor Tower's entrance is on the seventh floor.

Tom Riddle, who confided in no one and operated alone, might have been arrogant enough to assume that he, and only he, had penetrated the deepest mysteries of Hogwarts Castle.

And this is borne out by what we have been shown of Voldemort's thoughts about this Horcrux's hiding place.

the man duelling Percy

As stated, when his hood slips, this man is revealed to be Pius Thicknesse, the current Minister for Magic.

Exceptional character moments

Vincent Crabbe, turning on Draco Malfoy now that the latter and his father have fallen from power, then proceeding to use spells that he can't control.

Percy joking with Fred about duelling the Ministry of Magic.

Fred Weasley, dying with his last laugh still on his lips.