Ron's first thought was to bolt to the Library and tell Hermione and Luna what he'd worked out, but sense intervened before he'd gone more than a few steps. The Library was no place for a confidential conversation, even if Madam Pince would let them get away with it.

He hurried back to the Defence Against the Dark Arts classroom instead, bolted across the room and into his own quarters. Right, eavesdropping protections. He took out his wand. "Muffliato!" And then, for good measure, "Salvio hexia! Protego totalum! Cave inimicum!"

There. It wasn't as good as the protective wards he'd put on the place if it was somewhere that belonged to him, but he wasn't about to start messing with the castle's own protections, even if he didn't trust them to keep out someone Hogwarts felt had a right to be there. Still, I don't think even Dumbledore could get through that lot without giving me some warning.

He threw a handful of powder onto the fire and lay down in front of it. "Floo call to Harry Potter, 12 Grimmauld Place."

It wasn't long before Harry's face appeared in the flames. "Couldn't be without me for one night, eh?"

"That's right," Ron said, grinning. "I'm dying of loneliness being apart from you for twenty four hours."

Harry nodded approvingly. "As you should."

"Listen, is Ginny there?"

Harry looked wary. "Why?"

"Not because I'm about to come over all protective big-brother, you turnip. I know that you and she … well, I chose to think of it as pyjama parties and for Merlin's sake, don't tell me any different. But this concerns both of you. I mean, all of us — did you know Hermione's here, too?"

"Is she?" Harry grinned happily. "That's bloody brilliant, that is."

"And Luna, and Neville. And it's not so much 'bloody brilliant' as 'bloody alarming'. So get Ginny, will you?"

"I suppose we can tear ourselves away from braiding each other's hair at our pyjama party if there's dark magic afoot," Harry said, and disappeared from view for a minute. When he came back, Ginny was kneeling beside him. She was, Ron was relieved to see, wearing striped pyjamas and not some sort of seductive negligee. "So what's up?"

Ron gave them both a highly condensed version of the evening's events. "So it looks like Professor McGonagall has set all this up because she knows we'll work it out on our own, and she doesn't feel she can tell us," he finished.

"Right. I'll make sure I bring the map and the cloak tomorrow," Harry said. "Ginny, I know you were planning to stay in London and just come down for coaching —"

"Yes, but I can't now, can I?" Ginny said. "I can't do anything while I'm up on a broom coaching Quidditch, so I'll need a reason to be there the rest of the time."

"Got any injuries?" Ron asked. Ginny gave him a look: being Chaser for the Holyhead Harpies meant she was always carrying one injury or another. "Why don't you tell Professor McGonagall that you've got something bad enough to need a bit of a rest, and Madam Pomfrey's care?"

"She'll know I'm lying," Ginny protested. "We've got a top healer as our team doctor."

"Yes, but if she's really trying to get us all here under false pretences, she won't argue," Ron pointed out. "Now listen, when were you planning to get here tomorrow?"

"First thing, now you've told us this," Harry said.

"Good. I'll tell the others at breakfast, and we'll make a time to debrief. See what Hermione and Luna found in the Library, and if Neville got anything from Sir Nick."

"We need to make a list of which teachers it might be, too," Ginny said. "I mean, by order of likelihood. Then we'll know who to keep an eye on … for signs, I mean."

"Signs of what?" Ron asked. "We don't know what the trouble they're in is. It could be anything from a curse to being blackmailed by Rita Skeeter."

"Signs of anything," Ginny said. "I mean, we know them, don't we? At least, we know what they're like. They taught us for six years — seven, for Hermione and Neville and Luna. Anything odd is important, and what sort of odd it is might give us a hint of what we're dealing with."

"I hope it is Rita Skeeter," Ron said. "Or something we can just go and arrest. I have the feeling that the curse is going to take a fair bit of work, Harry."

"I bet we crack it in an afternoon," Harry said blithely. "If Professor Dumbledore was right, and it's Tom Riddle's curse, I'll just walk around the castle until my scar hurts." He put his hand to his forehead. "Cold … cold … warmer … warmer … hot …"

Ginny nudged him. "Don't joke."

"I'm serious," Harry said, grinning. "Partly. I do think I'll be able to feel Tom Riddle's curse. Maybe not through the scar, but he did have a certain inimitable style."

"Style?" Ginny stared at him. "You know very well his style was just a —"

"Ginny, Ginny, it's alright." Harry put his arm around her. "That's not how I mean it."

"Everyone has a certain feel to their magic," Ron explained. "Learning how to feel for it is something we do in Auror training. Like, your magic has a particular style to it. I wouldn't have been able to in school, but now, I could run across a charm or a hex you cast and say, oh, that's Ginny's."

Ginny relaxed a little, leaning against Harry. "I see."

Harry squeezed her shoulder. "I know what you thought. I know what he was like, in that diary. He fooled a lot of people, but Ginny, I promise you, I don't have the slightest inclination to admire anything about Tom Riddle's magic. Just recognise it." He looked back at Ron. "And you're sure Hermione's alright?"

Ron nodded. "She's not under any magical influence, she's just made a promise. And you know, I trust her judgement when she says it won't harm anyone."

"So do I." Harry sighed. "Still, it would be easier if she was as energetic as Professor Dumbledore when it came to looking for loopholes."

"I think Hermione thinks about the ethics of things a lot harder than Professor Dumbledore," Ron said.

Harry grinned. "I know she does. You know, he said once that he wondered if Hogwarts Sorted students too soon. At the time, I thought he was saying Snape should have been in Gryffindor, because of his bravery." Ron snorted. "But sometimes I wonder what Albus Dumbledore, student, would have made of himself in Slytherin."

"They should have major and minor houses," Ginny said unexpectedly. "You know, like Muggle universities, where you have a main subject and another subject? The Hat asked me if I wanted to be a Hufflepuff."

"You? A Hufflepuff?" Ron scoffed.

"Hard work, loyalty, and fairness," Harry said. "I can see it."

"I wanted Gryffindor, though. But what if, I don't know." Ginny paused, thinking, and the two men waited. "What if we had, say, Potions, Divination, Defence Against the Dark Arts and Herbology with the House we ended up in, and Flying, Charms, History of Magic and Transfiguration with the House we were almost in? Wouldn't we know more people, and be more friendly?"

"We were plenty friendly," Harry objected.

"Name me one friend you had outside Gryffindor!"

"Luna Lovegood," Harry said promptly.

"Name me two friends —"

"Cho Chang."

"A male friend you had outside Gryffindor!" Ginny snapped.

"Got me there," Harry admitted. "I don't think I would have been Draco's friend, though, even if I had been 'minor Slytherin'."

"Yeah, but Draco, right," Ron said slowly. "What if he'd been 'minor Ravenclaw' or something?"

"He wouldn't have been evil?" Harry asked, eyebrows up.

Ron shrugged. "I dunno. That's the point, though, isn't it? Ginny's point?"

He watched Harry think it through. That was one good thing about his best friend having 'pyjama parties' with his little sister: Harry gave serious consideration to ideas that came from Ginny, even if they were ones he'd dismiss immediately from Ron or Hermione.

"I suppose," Harry said at last. "I mean, look at Professor Snape. I bet the Hat offered him Gryffindor. He was the bravest man I ever knew, after all. But, after my dad … well, I can understand why he opted for Slytherin. But if things had been different … in those first years …"

"Yes, but," Ginny said, "that's sort of an argument for the way things are, isn't it?"

Both men stared at her. "Why?" Ron managed.

"Because if Snape and Harry's dad hadn't hated each other, Snape wouldn't have joined the Death Eaters," Ginny said impatiently. "And he wouldn't have told Voldemort about the prophecy, and Voldemort wouldn't have tried to kill you, and wouldn't have accidentally made you a Horcrux and been sent into exile. He would have just taken over back then."

"That's a bit fatalistic, isn't it?" Ron objected. "I mean, maybe Snape would have joined the Order of the Phoenix and he and Dumbledore and Harry's parents would have ambushed Mouldyshorts and won, right?"

"But that's not what happened," Ginny said.

"That's what Hermione calls telly-logical thinking," Ron said. "The idea that because things people did turned out one way, they always were going to turn out that way."

"Well," Harry said firmly, "When you're Headmaster of Hogwarts, you can suggest it to the Board of Governors. Meanwhile, we've got a mystery to solve and a curse to break."