Voldemort is mad and sends out some more terrible spells against the castle. His wand doesn't seem to be working properly for him, but it does enough: The castle's protections have broken.
The Death Eaters rush onto the grounds. Neville, fleeing from them, almost falls to his death on a bridge when it breaks, but he manages to scramble back up to safety. Whew.
It's total mayhem now, guys. Giants are suddenly rushing the grounds along with the Death Eaters.
The good guys retreat inside Hogwarts, with the bad guys in pursuit.
Suddenly, everyone is dueling.
Harry and Ginny run into each other and make some time for kissyface, but then it's back to work for both of them.
Harry arrives at a wall. Elsewhere, Ron and Hermione, who are looking at the Marauder's Map, realize he's probably in the Room of Requirement.
Meanwhile, Draco is trying to lead his buddies in pursuit of Harry. Oh great, just what we need right now. He sees that Harry has entered the Room of Requirement.
Inside, Harry finds the diadem. He hears all kinds of creepy whispering when he picks it up, which is definitely a sign he's found a Horcrux.
There's a problem, though: Draco and his friends, Crabbe and Goyle, arrive looking for Draco's wand.
Harry asks Draco why he didn't give Harry up to Bellatrix (at the end of the last movie). Draco doesn't answer, and his buddies tell him to finish Harry off.
Luckily, Ron and Hermione arrive, and Ron chases Draco and friends off.
Hermione and Harry go after the crown, which had been knocked onto a huge pile of other stuff.
Ron then comes running back, screaming. Crabbe has unleashed this crazy snake-monster thing made of Fiendfyre. It's like regular fire, but it's super hot and acts like a heat-seeking missile and is almost impossible to control or put out. And yes, it's as freaky as it sounds.
Suddenly, all the kids are on the run from the Fiendfyre, which they have no power to stop.
Ron, Harry, and Hermione get broomsticks to stay above the fire, but Harry refuses to leave Malfoy and Goyle (Crabbe…yeah, well, you can guess what the Fiendfyre snake did to him).
They manage to get them out of the room safely.
Draco takes off, and Harry and friends destroy the Horcrux just outside the room.
Voldemort feels it happen. He's getting weaker, guys…