"Repeat exactly the wordss of my emisssary. They have been chossen carefully to allow no trickss of wording, and I advise you follow this example in any future dealings in this tongue."

The boy who stood before the moonlit snake cocked his head to one side, as if he were himself imitating the motions of the snake. "Musst I ssweear to thiss now?"

And, from the snake, the hiss of dry laughter.

"You wissh to try your cunning against my own, boy? I do appreciate cunning in my desscendantss, even if I may dissapprove of the impulssess towardss which it iss directed. This Chamber will not refuse you for any passt attemptss to bypasss thiss precaution, you may try ass you wissh to deceive it; but you may not enter until you have ssworn."

The boy smiled faintly. "How very generouss of you. Iss that truly wisse, though?"

Again the hiss of snakish laughter.

"To give each Heir free rein to attack my defenssess? Perhapss not. But then, I did not ssay it would be precissely free."

A faint hiss. "And what do you mean by that?"

"There iss a price, boy, to trying the wardss upon my Chamber. My emisssary knows the time you first spoke to it, it will notice any excesssive delay. And the Monsster that waitss within for you knowss also, and the longer you delay and plot againsst me the lesss knowledge you will find within the Chamber for yoursself, when you finally enter." A faint smile. "Might be wisser, boy, to ssimply take the lore that iss offered, rather than wasste ssome in hopess of denying future Heirss. But if you think yoursself able to bypasss the wardss of Ssalazar Sslytherin upon thiss moment, then by all meanss make the attempt."

Harry felt a faint sickness in the pit of his stomach, as he watched through the Penseive, watching the game between Salazar and the Dark Lord. Salazar had been cunning indeed - perhaps more cunning than Harry was himself. His game was being played at a level Harry had never even thought of.

And he had already seen that it wasn't going to be enough to hold back Lord Voldemort.

Harry wanted to give up, right then, wanted to put down the Penseive and run from the room, but he needed to know, he needed to know, what this other Tom Riddle had done here.

So he watched, stood behind the eyes of that other version of himself as the boy stood before the silver snake and thought.

And a voice came from behind him.

"Close your eyes."

He obeyed instantly, for he recognized that voice. It was his own.

"Good. Slytherin's Monster is a Basilisk. That should be all you need to know."

Footsteps moving across a stone floor as that other Riddle walked to stand before the Patronus.

"I currently intend no actionss towardss the Chamber of Ssecretss or towardss anything I might find there that could in any way harm the ability of the Chamber to convey its ssecretss to ssubssequent Heirss of Sslytherin, and I do not anticipate my intentionss changing at any point in the future."

A snakish hiss, and his eyes opened again.

To claim victory or to admit defeat, he had six hours.

The boy was pacing through the halls of Hogwarts, deep in thought. His hand moved unconsciously, tapping against his leg, his face, his opposing arm.

And behind him, not in truth but in memory, walked another of himself, a Tom Riddle from forty years in the future, thinking the same thoughts.

The flaw in the oath had been clear enough. Perhaps it had even been intentional, since Salazar hadn't wanted to deny Heirs access to the Chamber entirely based on a single failed attempt (though that was looking increasingly foolish of him). But, whatever the reason, it made no statement about past actions, only about future ones. And that meant that, whatever plans he might make now, whatever actions he might take, no matter what they were, they would not interfere with his ability to make the promise in Parseltongue later. (Or, rather, earlier. He hadn't gone back in time yet, he was planning to do so as near to the end of his six hours as possible, just in case he thought of something in the interim that required the use of his Time-Turner.)

And yet, that didn't seem to be enough. Even if he somehow thought of a way to kill Slytherin's Monster right now (which didn't seem like it would be easy, given that he was a first-year student and it was a fearsome monster, and that he didn't even know how to find it at this point), all that would accomplish was denying the lore of Slytherin to himself as well. He needed to find a way to be able to kill it later, and yet he also needed to be able to honestly intend not to kill it later.

Four feet pacing back and forth in a hallway, two of them real and two of them memory, as those two Riddles walked and thought.

When his future self had spoken to him, it had identified Slytherin's Monster as a Basilisk, as if that fact specifically was important, as if it were some specific property of the Basilisk that would let his plan work.

He already knew the lore of the Basilisk - it was an obvious thing for a seeker of the Chamber of Secrets to learn - and he knew its weakness. The crowing of the rooster was fatal to the basilisk, however odd that might seem in a monster born from a chicken's egg.

(Neither Riddle knew that this had been an intentional feature. When Herpo the Foul had first bred Basilisks, he had been concerned that his creations might escape, might use the intelligence he had bestowed upon them to breed themselves, capturing chickens and toads and hatching more and more Basilisks, and so he had wrought a very specific weakness into them to prevent this. Herpo had thought himself very clever to take such a precaution, until the day the witch Evaine Alexander had invented the Chicken-Chucking-Charm.)

If you genuinely believed you would honor the promise, you would be able to give it in Parseltongue, even if you were wrong. If you could somehow trick yourself into thinking you wouldn't harm the Monster - but if a perfect Occlumens couldn't lie in Parseltongue, simple trickery wouldn't do.

A Confundus Charm or Legilimency might work, and False Memory Charms almost certainly would. He couldn't cast those himself, but maybe he could find an upper-year boy who owed him a favor, there were plenty of those by now, like the one he'd gotten to cast a Patronus and then leave, he'd need to get someone else to Obliviate them afterwards if he didn't want them to know, it would be tricky but should be doable...

...if he weren't in Hogwarts, where the use of any of those things on a student by anyone other than a Professor would instantly alert the Headmaster. And, while the Headmaster and the Professors did like him (well, most of them did), they didn't like him that much.

What had the exact wording of the oath been again? "I currently intend..."

The first Riddle paused in the hallway, his feet stopping where they were.

Then he was running, his feet pounding on the floors.

"I realize it's unusual, Headmaster, it's just..."

"Out of the question, I'm afraid." The words were stern, but Headmaster Dippett's voice was soft. "I realize Hogwarts is like a home to you, Tom, but Hogwarts policy clearly states that students should return to their regular dwellings over the summer except in the greatest extremity."

"So...there's nothing you can do then, Headmaster?" The voice of Tom Riddle was soft, wavering, sounding almost on the verge of tears, and Harry watched from behind him with a kind of sickened fascination, knowing he was seeing a master at work.

"I'm afraid not, Tom." Dippett paused. "Is there some reason you're asking?"

"N-no, no reason." The mask Riddle was wearing seemed to choke slightly, and there were tears gathering in the edges of his eyes. "I'm s-sorry, I shouldn't have asked. Th-thank you for your time, Headmaster."

The boy turned to go, and a hand on his shoulder brought him to a halt. He turned, and Headmaster Dippet's brown eyes stared into his own.

"Tom..." Halting, the words were, as if the Headmaster wasn't sure what to say. "Have...have they been treating you well? At the orphanage, I mean?"

The mask widened its eyes a bit, as if faintly panicked. "W-what? N-n-no, they've been p-perfectly kind. N-nothing to worry about." Each line a work of art, the pathetic, obvious lie of a panicked eleven-year old, one that could be seen through on the instant by any adult, while behind the mask the Dark Lord stood, watching and listening.

"I see." Sad now was the Headmaster's voice. "Well, Tom, I'm sure we can work something out..."

And, when it was over, no-one but that second Riddle saw the first one take off the mask and smile.

"You have learned well these passt yearss, Heir. It iss now time for me to bid you farewell. There is one final message I must bear you from Ssalazar Sslytherin, one favor he sseekss from you."

The boy's eyes were steady.

"Go forth and change thiss world. Whether you sseek good or ill matterss little. Too often we choosse neither path, too often we forssake both the path of good and the path of evil, to follow the path of whatever sseemss eassiesst at the time. You, the Heir of Sslytherin - we do not bid you choosse good over evil, but we do bid you choosse."

A slight nod. "I will. Thiss I sswear."

"And remember thiss: the Chamber of Ssecretss musst now remain clossed until the next Heir of Sslytherin sshould arrive to claim it."

And the Dark Lord smiled, and raised his hand.

Upon that hand there was a slim golden ring, and set into that ring there was a small diamond.

"What iss that?"

The Dark Lord did not answer. He slid the ring gently off his finger, bent down and laid it on the ground by the coils of Slytherin's Monster. The great serpent bent down, sniffed at it.

"A ring? What iss thiss?"

"For ssix yearss I bore it, all for thiss moment. I give it to you now, and bid you farewell."

And the Transfiguration Tom Riddle had placed upon that ring six years ago, that he had maintained for six years without pause, Transfiguring into the stablest form he knew in order to minimize the internal changes it would suffer over time, staying at Hogwarts over the summer in order to avoid detection by the Ministry's Trace, began at last to unravel.

For Salazar's oath required you to swear that you intended no action that might harm the Monster. But if you could find an attack on the Monster that could be triggered, not by action, but by the lack of an action...

The creature that appeared could be called an bird only in the loosest sense of the word. Six years of Transfiguration had taken a heavy toll, even in a form so stable as a diamond. The eyes were glassy and dull, the feathers mottled with blood, one leg would not bear its weight and it slumped against the floor.

But its throat was still nearly as strong as when it had been caught, frozen at the very instant of crowing, and as it died it managed to complete that act.

Harry rose from the Pensieve, gasped in deep breaths of air. It hadn't answered all his questions, there were still things he didn't know. Where had the body of the Monster gone, say? Destroying it with Fiendfyre or the Reductor Curse might or might not count as violating the oath - though if Voldemort hadn't planned to destroy the Monster's body, if the idea had come to him later, the oath wouldn't have bound him - but it wasn't mission-critical to know. Wherever the body had gone, the important thing was that there wasn't anything left here. Professor Quirrell might have been lying about the specifics of how it was done, but the general concept of 'nothing of value left in the Chamber of Secrets' had been true.

There had to have been other steps, too, he hadn't actually seen six hours of memories. Somehow Riddle must have figured out that Slytherin's Monster was a Basilisk in that time - though, to be honest, it seemed like that was pretty common knowledge - so that he could pass that information back to himself as a hint. Or maybe he would have figured it out anyway, and the stable time loop was one where he gave himself a hint to figure it out faster, like when Harry had gotten his Time-Turner; he still wasn't quite sure how that worked. The young Riddle had probably talked to the Transfiguration Professor too, to figure out what exactly he ought to do, unless for some reason he too had been given a rock from his father earlier in the year...but, again, that didn't seem particularly important.

The last few hours had been - well, Harry wouldn't say wasted, anything he could learn about that other Tom Riddle was potentially valuable, but suboptimally spent. One part of him was making remarks along the lines of I told you so, but Harry wasn't listening. He rose to his feet to leave...

And a hissing voice came from behind him.

"Well, thiss iss unexpected."