The high of the destruction of the second to last Horcrux was one the Sphinx Club got to ride for quite some time. There was little to no doubt that if they were to ever destroy the final horcrux, it would be during a battle with Voldemort, and therefore beyond planning the specific assault that would end the Dark Lord once and for all, there was little for the Sphinx Club to do on that front.
What they COULD do though, was study for their OWLs, and study they did. Reference books, mock exams, and notes they had borrowed from Cho and Cedric filled the Sphinx Club room as the majority fifth year students buckled down to push for the O's that they all desperately wanted.
"What is the switching spell?" Hermione quizzed, as Hannah idly chewed the tip of her quill.
"Simulanteous dual transfiguration that turns two objects into each other?" Hannah answered, slightly less confident than Harry imagined she would like to be.
"Not the textbook definition, but you are correct." Hermione said, flipping the index card she made around to show Hannah the actual definition from the book.
"Never understood why that one was the switching spell. I figured a switching spell would be a charm that would instantly swap the positions of two objects, or at least send one forward and one back." Tracey mused as she oversaw Daphne playing some kind of matching game. Strips of parchment with various potion brewing instructions were spread out on a table, with Daphne placing them in correct order for some simple potions.
"Probably a holdover. I think Mirabel's Transfiguration Primer mentioned that the spell wasn't originally thought to be a transfiguration spell when it was first created, they probably thought it did exactly what you're suggesting it does." Harry added as he reviewed some herbology notes Neville had left for him. For all the work he put in, herbology was a class he struggled with outside of the practical aspects, so the extra pointers from his best male friend were greatly appreciated.
Hermione flipped through the book Harry had mentioned, lightly chewing on her bottom lip as she looked over the passage. "She goes into a bit more detail, but you're not wrong." Hermione conceded. "It does make me wonder why they don't revert after a certain amount of time like other transfigurations tend to."
"Maybe it's like, a midway thing between what you two said? It's transfiguration by way of replacing every bit of it one piece at a time." Neville suggested, as he leaned back on one of the couches and closed his eyes for a moment. He'd been focusing on a practice exam they had worked on, and one of the practical elements of that was being able to change the color of a lumos light without recasting it. His eyes hurt from looking directly at the magical light for too long.
"I do not think such supposition would be appreciated in the written portion though." Hermione said, glancing at the one practice exam that had had the question. "Surely they would only want definitely provable information?"
"This one I'm looking at explicitly invites theories, and the note Flitwick gave me said that there's not really wrong answers, provided you can give some reasoning behind it. I would say its status as a permanent transfiguration would at least be a decent reasoning behind that." Harry said, holding up an exam he had looked at. "This one is specifically about Inferi, so different subject, but I can't see why an essay portion wouldn't let you have some theorization in it. Assuming it's not expecting just a short response like a definition."
"I'm quite worried what my OWLs will be like next year. You all have each other to help study. I'd only have Ginny and Astoria who aren't quite as focused as you are." Luna said quietly as she looked over her own homework, an assignment she had finished a couple hours ago, and only really kept working on it to continue spending time with the Sphinx Club without interrupting them.
"Astoria will get focused, even if I have to make her." Daphne said, determination and an evil smile on her face.
"You'll have all of our notes to go off of. Everything we're doing here? We'll keep stashed for you three to look over next year. I imagine your NEWTS will be the same way, although you'll need to push Neville and Lavender extra hard for their Care of Magical Creatures notes." Harry said, before crumpling up a piece of parchment and tossing it at Neville, forcing him to jolt up from where he had dozed off. "Nev! If you're tired you need to go to your dorm. Good sleep is important for actually committing all of this to memory."
"Have you been listening to your own advice Harry?" Susan asked with a raised brow as she looked to her fiancee, well aware of his general inability to 'turn off' his mind.
"He has been." Padma spoke for him, coming up behind him and wrapping her arms around his shoulders as she leaned over him, soaking in his essence for a moment. "I promised to put a good word in with Parvati for Terry if he made sure Harry went to sleep at a reasonable hour."
"You did not use me as a bargaining chip!" Parvati exclaimed, mock outrage in her voice.
"I didn't. At best I said he was a good guy, and outside of that quidditch obsession he is. I'd say that without him keeping an eye on Harry for me." Padma said with a shrug. "Your choice whether or not you accept his words. Besides, you could do far worse in our year."
"You're not wrong I suppose." Parvati said, rolling her eyes. "Although not all of us can be so lucky to have the love of our lives fall into our laps during second year like you did."
"I mean, you could always go ask Neville out. I bet you two would have a good time." Padma said, letting her gaze drift over to where Hannah was. The look the Hufflepuff girl shot Padma, and then Parvati, was nothing short of murderous.
"I value my life, thanks." Parvati said, before tapping her chin. "If he needs a second though…" Hannah's expression was entirely unreadable, whether she hated the idea, loved it, or had never even considered it was unknowable. Harry would have laughed if he didn't know it would bring her anger fully out on him.
He'd never seen Hannah TRULY angry, and he imagined it would be a terrifying sight.
Even more terrifying though, was the look that was on Professor McGonagall's face as she entered the Sphinx Club room. They were used to her normal strict look, the glares she'd give students who misbehaved, but her expression now was positively terrifying. It wasn't angry per say, or if it was, the anger wasn't directed at them. It also wasn't fearful, Harry was of the opinion that McGonagall couldn't even feel fear, her courage was simply that deep. It was something else, something determined and set, but apprehensive and rage-filled. Whatever it was, Harry didn't like it.
"Mr. Potter, you're needed for Phoenix matters." She spoke, looking him dead in the eye.
Harry liked that even less.
"Then let's go." Harry said as he stood up. "I'll be back, everyone. If I don't manage to get done before curfew, would you all mind just bringing my bag back to the dorms?"
"You've got it, love." Padma said, waving him off. "Go be big and important."
Harry sighed at her words, but wiped them off, before turning back to McGonagall. "I take it the news isn't good if you look like this." Harry said to her as they began to walk.
"It could certainly be better, but we shan't discuss it in the open halls." The strict professor said, as they made their way to Dumbledore's office.
The office had been magically expanded, and a grand meeting table had been transfigured, with chairs all around it. Dumbledore sat at the head, Snape to his left and an open spot that was typically McGonagall's to his right, which the Professor took without a word. Harry found his own spot, between Nymphadora and Sirius, as more Order members funneled through the headmaster's floo. In the end, not everyone from the Order was gathered, but the majority were, and those who were absent had someone who would speak in their interests. Bill, Molly, and Charlie Weasley for example, were absent, but with Arthur and Nymphadora there, they were certainly still represented.
"I thank you all for showing up on such short notice. As you know, I normally wouldn't hold such a meeting in the school, but times are becoming desperate, and I have been given information which you all need to be aware of, so that we can plan." Dumbledore said, his authoritative voice taking over. "Severus, please inform everyone what you have told me."
Snape stood up, and Harry could see the nervousness on his face, something which was certainly rather rare to see on the Potioneer. "The Dark Lord is planning an assault on Hogwarts." The words dropped like a brick onto the table. "He believes that Dumbledore and Potter are the only things standing between him and success, and he wants to clear the board in one fell swoop. To that end, he's trying to target the school immediately following exams, when everyone will be at their wits end."
"Dumbledore I can imagine, but the boy as a threat? Surely he'd think someone like Shacklebolt." Mundungus said, and Harry had to admit that it seemed like a fair question. He'd fought Voldemort for certain, but he was still a fifth year student. A talented one, but a student nonetheless.
"Harry's survived more direct confrontations with him than anyone other than Dumbledore." Sirius pointed out. "End of his first and second years, the Triwizard cup and then the fight at the Ministry in October. Even if he's not a match for him magically, Harry's disrupting his credibility by having bested him so many times as a child."
"Voldemort knows that too." Remus added, shaking his head a bit. "Harry all but called him out on it at the Ministry; forced him to retreat. He staged that breakout of Azkaban to save some face, but… he's vulnerable and desperate, and he knows that. One big swing to knock both of them off the board, to get rid of the only two people to ever tarnish his reputation? It'd probably be enough to quell any discontent."
"The why of it, I fear, matters not at this juncture." Dumbledore said, refocusing everyone inwards. "Severus, how many does he have now? I imagine he is intending to pull out all the stops for this. Hogwarts is not a location one can infiltrate lightly."
"Death Eaters number somewhere between two hundred and two hundred fifty. Maybe up to three hundred if favors are called in. Forty werewolves in Fenrir Greyback's wolfpacks. Then there's a family of giants he's convinced to fight for them. Ten of those I believe." Snape said, his tone clipped. "The Average Death Eater is admittedly not up to prior standards. Any half-decent auror could probably handle two of them with little issue, although the old guard are still formidable. I'm confident in my abilities to handle Bellatrix or Crouch, who are still his other top fighters, but there's perhaps only a handful of us who could properly stand against them."
"Hogwarts is not without its defenses… but can we really hold against such a force?" Minerva wondered aloud. "Attacking with the children present too… how could we keep them safe?"
"Umm.. I believe I may have a solution for that one." Harry said, speaking up. "Professor, can you have a map of the castle appear please?" He asked Dumbledore, who nodded. A map of the castle appeared on the table, a ghostly animated structure thereof appearing alongside it. "The Sphinx Club have been scouring the castle pretty extensively since before the year started." Harry said, as he glanced over a few of the floors. "We're really familiar with the layout now, because we were looking for places someone might hide something. Here." Harry pointed to a hallway. "Is the Room of Requirement. It's a secret room that can become whatever you need. It's really out of the way, not on any path that someone would take getting through the castle, and you can hide the door from the inside, such that only someone who knows to ask for it could find it. The students could be held in there easily, and you'd have to know about it to get inside. Voldemort knows it exists, but it's far from the first place he'd think to look for students." Harry also moved his hand to another section. "Less ideal, but still pretty safe would be the Chamber of Secrets. That one can only be opened by a Parseltongue, so myself or Voldemort, but we do know that simply mimicking the right word is enough."
"Those… aren't bad options for keeping the students safe if we can't fully evacuate them." McGonagall said as she looked over the options presented. "It doesn't solve the issue of how to hold the castle itself though. The order is only twenty-five strong, and even with the Hogwarts defenses, there's simply too much ground to hold."
"Well… we have some other allies who can help." Harry said, looking at everyone. "I know to you all we're just kids, but the Sphinx Club is ready for this. We've known for a long time that we'd need to fight. I was always going to be on the frontlines because of who I am, and they were always going to be in danger because they associate with me. We've got a lot of friends, and with your permission, we can call them in, and they can be a big help."
"Oh? And who could you call in that would make any kind of a difference?" Mundungus asked, sarcasm prevalent in his voice.
"Viktor, Ivan, Cedric, Marianne, whoever we could get Amelia Bones to spare." Harry said, looking over to everyone. "The Sphinx Club has 19 people, all of which are ready to give it everything we've got. Sirius, Remus, Nymphadora, and Dumbledore can vouch that I can stand on equal ground with Barty Crouch Jr. They watched me do it, and almost every Sphinx Club member is close enough in skill to me to be a challenge. I'm sure they'll stack up favorably against any Death Eater who isn't one of their best, and I'm sure Hermione, Padma, Daphne, or Neville could even stand up to the best."
"He does have a point. Remus and I are their defense teachers, and we're running out of things to teach them." Sirius said, looking over everyone. "Dumbledore, Remus, Flitwick and I have been training Harry all year, and he's a powerhouse. Those kids are insane for how old they are. Better than most anyone who did Auror training with me."
"I can attest to Mr. Potter's ability, and trust his judgement regarding his compatriots abilities." Dumbledore said, looking over to him. "That puts us at just over forty members, assuming we can't find some other assistance." Dumbledore hummed for a moment, glancing over the layout of the school. "With those, and Hogwarts defenses… Perhaps there is something we can do after all."
"Well… I have a few other ideas… Do you think Professor Sprout would mind us using her greenhouses?" Harry asked, as he began pointing out some other ways Hogwarts could be defended. They had just under a month to prepare, alongside keeping up the appearance that Hogwarts was none the wiser of the upcoming attack. Hogwarts would hold though.
Harry was sure of it.