The next morning, after they had eaten breakfast, ten students and two practical-joke merchants, with Harry at their head, made their way to the seventh floor, where the gargoyle guardian of the Headmaster's office awaited them. "Password?" it enquired.
"Watchtower!" said Harry.
"Quite right," said the gargoyle, and leaped aside to reveal the ascending spiral stairway. Each member of the curious procession selected a step (except Neville, who preferred to perch himself on the banister next to Hermione), and the staircase bore them up swiftly and silently to the top of the Headmaster's tower.
When they arrived, they found that their elders had preceded them: Hagrid was standing on the Headmaster's desk, arranging a number of Pensieves according to Dumbledore's instructions, while Snape stood by in a corner, watching the proceedings with his gleaming-red Martian eyes.
Dumbledore glanced up as the costumed youths filed into the room. "Ah, welcome," he said. "Everyone find a seat; we'll be ready for you shortly."
"What's that?" Ginny whispered to Harry, pointing to the Pensieves, as they and their Leaguemates seated themselves on various chairs, stools, and futons that the Headmaster had thoughtfully strewn about his office that morning.
"It's a kind of liquefied memory," Harry whispered back. "You put your face in it, and you see a scene from the past the way the person you got it from remembers it."
Ginny wrinkled her nose. "And Dumbledore expects each of us to stick our faces in all six of those?" she said.
"No, I think not," said Dumbledore. (Ginny, who had forgotten about the Headmaster's super-hearing, started guiltily.) "Pensieve fluid is a curious substance, as much energic in nature as material; I think it likely that Miss Lovegood will be able to absorb all these memories into that marvellous ring of hers, and thence to project them onto the wall so that all of us can see them at once. If she is willing, of course," he added, with a respectful glance toward the young Ravenclaw.
"I'd be glad to," said Luna amiably.
As she walked over to the first Pensieve and began drawing the substance inside it into the bezel of her ring, George (who, along with his twin, was quite familiar with Pensieves, thanks to a certain escapade in their second year), extended his neck and glanced into each of the stone basins in turn. Most of them contained the same silvery, transparent not-quite-liquid that Pensieves usually contained, but the fourth one from the left was a different story; the material inside that was dull green, and of a consistency that made it look not so much like a magical mist as like an eldritch slime.
"Eurgh, that's a nasty one," said George, screwing up his face in such a way as to make Cho burst into suppressed giggles. "Whose memory is that?"
"Mine," said Snape dryly. (Cho giggled even harder.) "By derivation, at least. It seems that Professor Slughorn was rather reluctant to part with a particular memory, and, as Mr Potter's efforts to induce him seem to have proved unavailing –" (Harry flushed beneath his mask, and Snape's eyes seemed to glow a little brighter in triumph) "– the Headmaster decided that the simplest expedient would be to have me glance into his mind, and to use my memory of reading his memory in place of his memory itself."
As George tried to work that one out in his mind, Luna stuck her ring into the last Pensieve and sucked up the fluid therein. "Ready, Headmaster," she said.
"Excellent," said Dumbledore. "Get settled, everyone. Harry, since you have already seen the first three of these memories, you may, if you wish, find something else to occupy yourself for the next few minutes. I have heard of your recently-acquired antipathy to stillness, so..."
Harry shook his head, and grinned. "No, Professor, that's okay," he said. "I don't mind sitting still for a little while, if it means I get to see you in that suit again."
"What's this?" said Fred, with a look of interest.
"Very well, then," said Dumbledore. "As soon as Dobby arrives, we can..."
He was interrupted by a pop! so loud as to be almost deafening. There was a slight shimmering in the air beneath Phineas Nigellus's portrait, and Dobby appeared in all his six-foot, red-clad glory.
"Ah," said Dumbledore. "Speak of the devil. Very well, then; Miss Lovegood, if you please?"
Luna nodded, and aimed her ring at a space on the wall that had apparently been cleared of portraits for this purpose. A green beam, rather like that of a movie camera, shot out of the ring and projected a picture onto the wall – a picture that Harry recognised as the opening scenes of Bob Ogden's visit to the Gaunt house. The sixteen super-wizards settled themselves in, and watched the story of Voldemort's rise unfold.
"This is your final word?" said the bright-green Tom Riddle in the picture.
"It is," said the equally verdant Dumbledore.
"Then we have nothing more to say to each other."
"No, nothing. The time is long gone when I could frighten you with a burning wardrobe and force you to make repayment for your crimes. But I wish I could, Tom... I wish I could..."
As Riddle turned and strode from the office, the picture flickered and faded out, and Luna lowered her arm and began massaging it with her left hand. (Nearly an hour spent holding it extended, with only brief breaks between memories for Dumbledore's comments, had naturally left it quite stiff.)
For a few moments, no-one said anything; then, with an awkward cough, Ron observed, "Well, that was interesting."
"So I thought," said Dumbledore dryly.
"So that's what a Horcrux is," Hermione murmured. "A piece of your soul that you've sliced off and hidden in an object somewhere." She paused. "In a diseased way, that's actually rather brilliant."
"Correction, Miss Granger," said Snape. "The Horcrux is the object itself. The fragment of soul has no special name."
"Oh." Hermione flushed; it had been a long time since a teacher had had occasion to correct her understanding of his subject. "Well, all right, then. It's still horribly ingenious."
"And You-Know-Who made seven of these?" said Ginny.
"Six, I make it," said Dean. "If he wants a seven-fold soul, he'd have to keep some of it in himself, wouldn't he?"
Dumbledore nodded approvingly. "Very good, Mr Thomas," he said. "Yes, we are looking for six Horcruxes – or, rather, four, as two of them have already been destroyed. Voldemort's diary, which Harry rendered insolvent four years ago, was certainly one of them, and Marvolo Gaunt's ring –" here he raised his hand to reveal the broken ring glinting on his finger "– was another."
"So what's that leave, then?" said Hagrid. "That cup o' Hufflepuff's an' that locket o' Slytherin's, I s'pose – tha' makes four – but what'd the other two be?"
"Well," said Dumbledore thoughtfully, "following the same pattern, it would be logical for us to look for something once owned by Gryffindor and something once owned by Ravenclaw. However, as the only two known relics of Gryffindor are in this office right now –" he gestured to the sword above his chair, and then to the Sorting Hat on the shelf above Emerald's head "– and as neither of them have ever been in the vicinity during one of Voldemort's murders, that line of inquiry, at its most profitable, would still leave us with one Horcrux to account for." He stroked his beard. "I wonder, now..." He turned and looked at Snape wordlessly; Snape looked thoughtful for a moment or two, then nodded slowly.
"What?" said Draco. "What's going on?"
"Nothing, Mr Malfoy, nothing," said Dumbledore. "Your Head of House and I were merely... ah... sharing a few thoughts.
"You seem distracted, Miss Potter," he added, as Draco turned away with an irritated snort.
"Hmm?" Emerald blinked. "Oh, sorry. I was just thinking how different that whole story was from the story Mum and Dad used to tell Hal and me. I mean, I know I ought to be used to that by now, after all the little surprises your Binns has slipped into his lectures, but..."
Dumbledore frowned. "You mean that Voldemort did not use Horcruxes in your universe?" he said.
Emerald shook her head, causing her blood-red hair to ripple about her shoulders like the Black Lake beneath the setting sun. "Oh, no," she said. "Our Voldemort's scheme was completely different. As near as I could ever make out, he was trying to work out an Arithmantical formula that would give him total mastery over living things everywhere... or something like that."
"Ah," said Dumbledore. "A pity. I had hoped that you might be able to tell us the hiding places of the various Horcruxes. As it is, I suppose we shall have to trust to old-fashioned detective work."
"Suits me," said Neville, tapping his mace against his hand. "So we find out where You-Know-Who put the things, and then we go in and smash them, is that it?"
Snape laughed scornfully. "If only it were that simple, Mr Longbottom," he said. "You don't know, I suppose, that a Horcrux can only be truly destroyed in a handful of ways. Because of the potency of the magic involved in creating it, he who wishes to demolish it must use an equally potent destructive agent."
"Such as?" said Hermione, pulling out a quill and a piece of parchment from a nearby drawer.
"The obvious candidate would be basilisk venom," said Snape. "That is, I understand, what Mr Potter used to dispatch his seventh of the Dark Lord. Then, let me see, the Shamir would likely do the job, if it hadn't been lost for the past three millennia; so would Fiendfyre, or Quandoquidem Lightning; so would..."
"My ring?" Luna suggested.
Snape hesitated, then shook his head. "No, I think not," he said. "An Oan power ring, I understand, derives its power from the wearer's will – and I don't fancy, Miss Lovegood, that your will is destructive enough to unmake a Horcrux."
"Oh," said Luna thoughtfully.
"What about that dead basilisk that Harry left in the Chamber?" said Ron. "Would it still have enough venom in it to take out a Horcrux or two?"
Snape considered. "Possibly," he said. "Under the proper conditions, basilisk venom has been known to take as much as a quarter-century to dry fully."
"So we might have an anti-Horcrux weapon right here in the castle?" said Ginny.
"Oh, no," said Dumbledore. "The news is a bit better than that. We certainly have one anti-Horcrux weapon right here in the castle, and we might have several more. You see, the sword that Harry used to kill Voldemort's basilisk –" here he gestured again to the sword above his head "– was made of goblin-tempered steel, and therefore absorbs the virtues of whatever it comes into contact with – such as, for example, the Horcrux-destroying properties of basilisk venom.
"In fact," he continued, "since we have such an array of anti-Horcrux weapons, I think it might be best if we divided into teams and searched for the Horcruxes individually. Let me see..." He gazed about the room speculatively, his eyes marking each Leaguer in turn. "Yes. Three teams, of three members each. Mr Longbottom, you will lead the search for Slytherin's locket; I would advise Hagrid and Miss Potter as your companions. Mr Weasley, you and your siblings will search for the cup..."
"I thought you said three members to a team," said Fred.
"For the sake of simplicity, I am willing to count you and your brother as a single member," said Dumbledore. "And I myself will search for the mysterious fifth Horcrux, accompanied by... let me see... I think Miss Chang and Mr Malfoy would be the most help to me. And, Severus, you will, of course, see about that other matter."
Snape nodded.
"Excellent," said Dumbledore. "Mr Longbottom, you take the sword – and, Harry, if you will do me the favour of opening the Chamber entrance for me, I will go extract the basilisk's fangs and divide them with Mr Weasley. And then, I suppose, I shall have to see about getting papers drawn up to excuse the six of you from classes for the next few days, and arranging for Professor Grubbly-Plank to... yes, Miss Lovegood?" he added, catching sight of Luna's raised hand.
"I was just wondering what the rest of us were supposed to do," said Luna. "You didn't assign any sort of mission to Harry, Hermione, Dobby, Dean, or me."
"Ah, yes," said Dumbledore. "I am afraid I assumed it was obvious. It will be the task of you five – and of Professor Snape, who, when he is not actively attending to the matter I mentioned, will continue to teach his regular classes – to stand guard over the castle, and to summon the rest of us in the event of an attack. For I think it unlikely," he said, his face darkening, "however discreet we are, that Voldemort will not eventually learn what we are doing – or that, having learned, he will not attempt a counterstrike at Hogwarts itself. In which case, it will be as well that a substantial amount of our power should have remained on the grounds."
Nearly every member of the League shuddered at the Headmaster's ominous implications. Luna, however, merely nodded obediently, as if Dumbledore had simply asked her to sweep his office while he was gone. "All right," she said. "I think we can manage that."
"I am gratified to hear it," said Dumbledore. "Come, Harry; let us to the Chamber."