Tom Marvolo Riddle, as Hermione had determined, was Voldemort's real name. The fact that a diary from 1942 had shown up, a diary that just happened to belong to the Heir of Slytherin, that just happened to have been found by a Gryffindor girl who had light-colored hair and hadn't had her growth spurt yet, that said girl had decried as evil, was definitively, decisively, and incredibly suspicious.
Hermione was excited beyond all belief.
She was certain she had just found a huge key into the entire Heir of Slytherin and Chamber of Secrets debacle. She had to force herself to stay calm, making sure to confirm the facts she knew before playing around with what was certain to be an incredibly dangerous object.
First, she went to back to Moaning Myrtle's bathroom, sneaking away alone during lunch to do so.
"Yes, I've seen her before," Moaning Myrtle confirmed. "She's been around a few times. She was here very late, the night right before the winter break." She frowned. "She never even talks to me when she's here, though – acts as if I don't even exist—"
"What does she do, when she's here?" Hermione asked, tucking away the photo of Ginny Weasley she'd brought. "Does she use the toilet?"
"Hardly," Moaning Myrtle sniffed. "She just kind of hisses at the sink and makes it go down."
Hermione paused.
"'Makes it go down'?" she questioned carefully, and Moaning Myrtle scowled.
"Well, I don't know what else to call it," she snapped. "She hisses at the sink, and the sink sinks down into the floor, exposing a big pipe. Sometimes she goes down in the pipe; sometimes she just hisses down it and leaves."
"Which sink?" Hermione asked, moving further into the bathroom. "Is it a particular one?"
"That one," Myrtle said, gesturing. "It's never worked."
Hermione examined the sink, dirty as it was. It seemed just like all the others, though the taps didn't work, as Myrtle had said, and as she tested the taps, she felt something on the side of one.
There, etched into the side of the copper, was a tiny drawing of a snake.
Hermione felt her heart jolt.
"And you say she goes down into the pipe?" Hermione clarified, and Myrtle sniffed.
"She does. I certainly don't," she said. "It's already dirty enough in here, what with no one caring enough about me to ever clean the bathroom. I'm certainly not about to go into a sewer."
Hermione tilted her head, evaluating Myrtle carefully.
"Have you told anyone else about this?" she asked. "The Headmaster, any professors? Anyone about noticing a small girl hissing at a sink and opening up a secret passageway?"
Myrtle's face turned nasty.
"I have not," she said. "No one's ever cared enough to ask. I told you – no one cares about me!"
With a wail, Myrtle leapt from her seat in the air and plunged into one of the toilets. Hermione wasn't quick enough to dodge; she left the bathroom with satisfaction at having solved a puzzle, but with fairly sodden robes.
(She did pause in the kitchens, though, kindly asking if a couple House Elves would terribly mind cleaning Moaning Myrtle's restroom if they had the time, even though it was always marked Out of Order.)
The second thing to do was research. All Hermione knew so far was that the diary was evil, and that if you wrote in it, someone wrote back.
Hermione was fairly certain she knew who that someone might be.
Hermione did her best in the library that she could, to no avail. She couldn't find anything useful that could explain such a phenomenon, though she did find a spell to link parchments to other things, which she tucked away in her mind. Linking two parchments together to 'pass notes' in class would be exponentially easier than actually trying to get away with passing notes.
With not many options left, Hermione turned to the books in her trunk, the trunk she was "keeping safe" for another, carefully going over the titles, staying away from those that were belted shut. There were lots of books on Dark magic, with several on Dark rituals and Dark spells, and quite a few on spell creation. Not wanting to actually have to read through books on Dark magic, Hermione used the indexing spell that was on the books in the Hogwarts library. To her dismay, none of the books responded to the search terms "diary", "person trapped in a diary", or "evil book that writes back".
There was nothing else for it.
The third thing to do was test the diary.
Hermione wasn't sure what she was getting herself into, but she was faintly terrified about it, so she was very careful and methodical about the entire thing.
"What do you mean, you're going to test something evil?" Blaise wanted to know.
Hermione held up her hands. "Look, it's hard to explain. All I need is for you to make sure I check in with you in two hours, and make sure I answer a verification question correctly."
"A verification question?" Blaise frowned. "Like a password?"
"Like something only you and I would know," Hermione clarified. "Passwords can be overheard and stolen. Like… where did you take me in Diagon Alley over the summer?"
Blaise grinned. "The Hopping Pot. You met my mother that day."
"Exactly." Hermione nodded.
Blaise looked thoughtful. "I can come up with something like that."
"If I don't come and check in with you in two hours, or you see me in the common room and I don't answer the verification question correctly, I need you to run and get Professor Snape," Hermione told him seriously. "Do you understand?"
"Are you summoning muggle demons?" Blaise looked excited. "That's not fair, to do that without the rest of us."
"I am not summoning demons," Hermione snapped. "Look, can't you just do this thing for me? It'll really help out."
Blaise smirked at her, though concern flickered in his eyes.
"Alright, Hermione," he told her. He hesitated. "Be careful."
"I will," she promised.
Once in her dormitory, Hermione carefully isolated herself, charming her bed curtains shut for security. She put everything else away, save her wand, a quill, an inkpot, and the diary.
She inked the quill carefully, looking at the diary lying open in front of her innocuously, and took a deep breath.
"Okay, you can do this," Hermione told herself. "It's just a diary…"
Fighting to keep her hand from shaking, she wrote: Hello. My name is Hermione.
Her eyes went wide as the ink sank into the page, before the ink oozed back out, new words forming.
Hello Hermione. My name is Tom Riddle. How did you come by my diary?
Hermione bit her lip hard, mind rapidly considering her options.
I got it off a girl named Ginny, she settled for. She didn't want it anymore.
The ink oozed out again, neat handwriting forming.
Might you be Hermione Granger? the handwriting asked, and Hermione felt a shiver run down her spine, prickling.
She hadn't wanted to tell the diary her full name. But somehow, he'd already known.
I am. Hermione wrote back. You've heard of me before?
The diary's text now had a slight twist to it, as if amused.
How could I not? You're the only New Blood of an epoch, apparently, and the only person with muggle parents to be sorted into Slytherin in a century. Ginny was fascinated and terrified by you.
Hermione swallowed hard. She wasn't sure if he was teasing or threatening her.
Glad to know I made an impression, she wrote back, playing it off.
Oh, to be sure, Hermione, the diary responded. You definitely make an impression.
The response dissolved, the ink reforming, another message coming through, one that made Hermione's blood run cold.
Of anyone else who might have come by my diary, I'm rather glad it was you.