Where exactly is Tom Riddle's diary?
This had been the question occupying Jon's thoughts for some time.
Especially after the professors and Filch had practically turned Hogwarts upside down and still found nothing.
Could someone have taken it out of the school?
Unlikely... After learning of the diary's existence from Ginny Weasley, Dumbledore and the other professors would have heightened their vigilance and inspection efforts. Allowing a Dark object like that to leave the school so openly was nearly impossible.
Could it still be in the hands of a new host?
That didn't seem likely either... With how thorough the search had been, it was hard to imagine it hadn't been found. Even Horcruxes couldn't escape detection by Dark magic detectors—otherwise Lucius Malfoy wouldn't have bothered handing the diary to Ginny in the first place.
Then perhaps it was time to think about it from another perspective...
Like, from Voldemort's point of view.
The Basilisk had already been slain, and as the Parselmouth controlling it, Voldemort would've sensed that. Ginny Weasley had also been captured alive—and given the connection between their souls, Voldemort would've noticed that too...
As a fragment of soul within a Horcrux, it wouldn't stand a chance against Dumbledore. With the Chamber of Secrets exposed and its own existence revealed, continuing to control its host or pulling any more tricks would almost certainly lead to discovery and destruction—it was just a matter of time.
That left it with only two reasonable options:
First, try to use a new host to escape the school—but that had a very low success rate.
Second, have the new host hide it somewhere unknown inside the castle, wipe the host's memory clean, and then lie low, waiting for the right moment to return.
If Jon were in the diary's place and thinking rationally, he'd absolutely choose the second option.
The soul inside the diary was from when Voldemort was seventeen. He probably hadn't yet reached the level of mental fragmentation seen in his later years—he should've still been capable of rational thought.
Which made the answer pretty obvious...
Inside Hogwarts, what place would Voldemort consider known only to himself—secluded and safe?
That's right—the Room of Requirement where Ravenclaw's Diadem was hidden.
The probability? Over 70%, easily.
Which meant, every day Jon spent time in the Room of Requirement, he was likely sharing space with two of Voldemort's Horcruxes. Even if they weren't on the same "plane," the thought was still kind of thrilling!
...
Jon had actually come up with this theory more than a week ago.
He just hadn't acted on it yet... Even though he'd been using the Room of Requirement for over half a year, he'd never once entered the version of the room where Ravenclaw's Diadem was hidden.
Horcruxes were still Horcruxes, after all—infused with powerful Dark magic. The diary even had a degree of consciousness and had absorbed part of Ginny's soul. As a first-year wizard without a wand, naive and idealistic, Jon knew well enough to be cautious.
He had already come up with several ways to deal with Horcruxes, but the risk of something going wrong was always there...
So avoiding direct contact was definitely the smarter move.
A wise man doesn't stand under a collapsing wall!
Should he just go with the usual method and hand them over to a teacher?
But that would mean exposing the Room of Requirement, his secret base—that didn't seem worth it.
After all, he still had several years left at Hogwarts.
And really, there was no rush to destroy the Horcruxes... At this point in time, Voldemort would still be stuck in Albania, gnawing on rats for more than a year. Then he'd need to head to Little Hangleton to absorb Nagini's venom for another year...
While it was a bit pitiful to imagine the Second Dark Lord living such a miserable post-prime life, it also meant Jon had at least two years to work with.
Still, there was one thing he had to do first... and that was confirm whether his guess was correct.
...
On the first day of the Easter holidays, warm sunlight bathed Hogwarts Castle.
It was the first truly nice day the Scottish Highlands had seen in months—clear skies, the kind of blue that looked just like forget-me-nots, and a crisp breeze that hinted at the coming summer.
Students who'd stayed on campus had come outside, reading books and chatting in the sunshine.
Jon walked alone to the eighth floor, across from the tapestry of the trolls beating Barnabas the Barmy. After making sure no one was around, he softly called out:
"Klein?"
With a crisp pop of air, several House-elves appeared before him.
At the front stood Klein, the one he was most familiar with.
"Klein received Mr. Jon Hart's request yesterday, so Klein brought his friends and waited here early!" the House-elf said humbly.
"Thank you, Klein... Did you check the Room of Requirement?" Jon bent down and asked with concern.
"Yes, Mr. Jon Hart..." Klein leaned in close to his ear and whispered, "Following your instructions, Klein entered the room where things are hidden and found the two items you mentioned... a black, worn-out diary, and a golden diadem engraved with an eagle. They're both inside, together..."
"You told Klein not to touch them, so Klein pretended to be looking for something else and only passed by them. Klein didn't even tell his friends..." the House-elf added.
"Thank you so much, Klein!" Jon took its small hand and smiled.
"To help Mr. Jon Hart is Klein's honor. Every House-elf in the kitchen would love to do the same..."
...
With the help of a few House-elves, Jon was almost certain that the Horcruxes were indeed there.
Even the soul fragment in the diary would have a hard time detecting anything... After all, Voldemort looked down on House-elves entirely.
That made the next steps simple—just let the two Horcruxes sit in the Room of Requirement for a few years.
There was no point in destroying them now.
Better to wait for the perfect moment.
Jon had long drafted a plan for destroying them. Sure, he couldn't get into the Chamber of Secrets, retrieve the Basilisk's fangs, or pull out Gryffindor's Sword...
But that didn't stop him from using other tools!
He could wait until after the third-year Triwizard Cup final—or during the fourth-year battle between Dumbledore and Voldemort at the Ministry of Magic.
He'd time it just right and pre-order a barrel of aqua regia (a mix of nitric and hydrochloric acid) and a tank of liquid nitrogen.
Then, when Voldemort started his fight, Jon would head to the Room of Requirement, fetch the two Horcruxes, and give him a taste of the ultimate "fire and ice" treatment.
Yep, that was the plan!