A/N: I've never seen anyone write the Battle of the Astronomy Tower from another character's perspective, and I can understand why. The whole action sequence in Chapter 28 is difficult to follow. For example, I think Draco let six Death Eaters in, but it's written in such a way that the number seems to change.
I finally got around to watching the HBP movie, mostly to see how it portrayed the fight scene between the Aurors, students, and DEs. But it turns out that it doesn't portray it at all. Harry just chases the DEs by himself. I think they sort of moved that fight to Burrow, but it didn't make much sense there. I kept wondering why the adults didn't simply Apparate the hell away from the Burrow, especially considering how important Harry's safety was. And the burning of the Burrow was dramatic, but it proved to be entirely pointless, since it had no impact on anything in that movie or the next.
So here is my best effort at piecing together the original Astronomy Tower sequence, in a way that hopefully makes sense.
"You believe Harry now, even though he still has no evidence?" Luna gazed at Hermione, wondering what had changed the other girl's mind.
"Well," Hermione waffled. "I'm still not entirely convinced, but it doesn't hurt to keep an eye on Malfoy, just in case."
"That's a step in the right direction, at least," Luna said with a nod.
"So you'll help us?" asked Ron.
"Of course. This is the closest I'll get to another DA meeting."
"I think Harry has a lot of nerve asking the DA for help when he called it off at the beginning of term," huffed Ginny. "Luna and Neville were really disappointed."
Hermione bit her lip. "I know, and I'll understand perfectly if you don't want to help."
"I'll pitch in," said Ginny, putting her hands on her hips, "but I think they have the right to tell Harry they told him so."
"Someone should make Harry understand how important the DA is," agreed Luna. "He forgets sometimes. It's not his fault, though. His head is full of wrackspurts."
"Where is Harry, by the way?" asked Neville.
Ron and Hermione exchanged a look.
"He went with Professor Dumbledore to Hogsmeade," said Hermione.
She received skeptical stares from Luna, Neville, Ginny, and all the portraits that were eavesdropping.
Ginny narrowed her eyes. "What are they up to?"
"Look, we can't tell you. We promised Harry we wouldn't."
"I'm his girlfriend! I have a right to know!"
"Also," said Luna, tilting her head, "you don't have to keep a promise if it's stupid."
"It's save-the-world business, all right?" said Ron. "If the wrong people found out what they were doing, it would be bad for all of us."
"The wrong people! Doesn't he trust me?" She waved her arms toward Luna and Neville, who were standing on either side of her. "And what about them? They've already proven themselves loyal and trustworthy."
"I see your point, Ginny," said Hermione. She glanced at Ron, who held up his hands.
"You can tell them if you want. If Harry finds out, I'll just deny that I had anything to do with it."
Hermione glared at him before facing the other three students. "All right, I'll tell you as much as you need to know," she said, choosing her words with care. "But you have to swear not to breathe a word of it to anyone, not even Harry."
"We swear, don't we?" She turned to Luna and Neville, who nodded their confirmation.
Luna kept her own advice in mind, however.
"Right," said Hermione. She glanced around the empty passage and flourished her wand at the portraits.
"What was that?" asked Neville.
"Oh, that was the Muffliato jinx." Hermione pocketed her wand. "It fills the ears of the targets with an unidentifiable buzzing sound, so they can't listen in on our conversation. I hope it works on portraits."
"So that's the Tinnitus spell!"
Hermione's jaw dropped. "You knew?"
Neville shrugged. "Dean, Seamus and I noticed the buzzing at the same time, and you'd already told me about the old Potions book with the mysterious spells. It wasn't that hard for the three of us to work out."
Ginny tapped her foot. "This is all fascinating, but I'd really like to know where Harry and Dumbledore went."
"Well," said Hermione, taking a deep breath, "I honestly don't know their exact location, but they're looking for a rare artifact that belongs to Voldemort."
Ron, Ginny, and Neville shuddered.
"Oh come on." Hermione rolled her eyes to the ceiling. "If we're going to fight him, we can't be afraid of his name, can we?"
"No, of course not," agreed Luna. "Now, could you tell us about this artifact?"
"I can't tell you too many details, only that Harry has to find and destroy it in order to defeat Voldemort once and for all."
"All right," said Luna, accepting this answer for the moment. "What can we do to help?"
"The five of us can help by keeping Malfoy and Snape in check until Harry and Professor Dumbledore come back. Ron, Ginny, Neville, you'll guard the Room of Requirement. Luna and I will wait outside Snape's office."
The others nodded, and the group split up to head toward their posts.
Ron, Ginny, and Neville waited in front of the Room of Requirement for half an hour. Ginny spent much of this time wondering aloud where Harry was, and how his covert operation was going, and Ron reiterated that he really didn't know much more than Ginny. Neville couldn't think of anything beneficial to add to the conversation, so he quietly gazed at the wall.
Then, right before his eyes, the door appeared, and out stepped Malfoy. He had a deep frown, and he clutched a severed, shriveled arm in one hand and a black bag in the other.
Ginny had the swiftest reflexes. "Impedimenta!"
Before she finished her incantation, Malfoy threw black powder into the air, and the hall was swallowed in darkness.
"What the hell?" asked Ginny. "Lumos! Incendio! Expelliarmus!"
Nothing happened. Many footsteps hurried past them.
"It's Fred and George's Peruvian Instant Darkness Powder," explained Ron. "It extinguishes all light, even from magic."
Neville swished his wand in the air. "Finite Incantatem!" It had no effect.
"Wait, I've got an idea," said Ron. "Expecto Patronum!"
Still nothing happened.
"Damn, I thought for sure that would do the trick," said Ron.
"Now what?" asked Neville. "How can we fight an enemy we can't see?"
"We'll just have to follow the sound of their footsteps until the powder runs out."
"When will that be?" asked Ginny.
"Don't know." There was a pause. Then Ron exclaimed, "Felix Felicis!"
"Come again?" asked Neville.
"Harry's luck potion," clarified Ron. "I have half of what's left. Hermione told me to wait until we really needed it. Here Ginny, ladies first - you're not Ginny."
"I'm over here."
There was the sound of a stopper popping out of a bottle. "All right Ron, you next."
By the time the vial reached Neville, there were only a few drops left, but he had no way of knowing how much there had been to begin with.
"Down the hatch," said Neville.
"Right," said Ron, with renewed vigor. "Let's catch some Death Eaters!"
He careened blindly through the corridor, Neville and Ginny on his heels.
Suddenly the lights came on.
"Weasleys! Longbottom! What in Merlin's name is going on?"
It was Professor McGonagall. Lupin, Tonks, and a tall red-haired wizard climbed the staircase behind her.
"Bill!" cried Ginny, rushing forward to hug him.
"All right, Ginny?" asked Bill, returning the embrace.
"All right. Did you see Malfoy and the Death Eaters?"
"That sounds like a band name," muttered Tonks.
"No," answered Bill.
"I just reached the top of the stairs when I saw you three barreling out of that ominous darkness," added McGonagall. "Are you certain there were Death Eaters?"
"Er, ninety percent certain," said Ron.
McGonagall pursed her lips. "Have you any idea which direction they went?"
"It sounded like they went that way." Ron pointed down the passage.
"Then let's hurry."
A/N: This chapter needed more reworking than the others; originally Hermione told Luna, Neville, and Ginny about the Horcruxes, but I decided that was TMI for them.