Tom Riddle's diary was generally kept underneath Hermione's pillow or in the drawer of her nightstand with a Keep-Away Jinx on it. She still drained her magic into it frequently before bed, as it worked much faster than trying to levitate furniture to exhaustion, and it was fine, so long as no one else tried to pull Tom Riddle out of it. And this way, with the diary constantly charged, should Hermione have need of Tom, she'd be able to pull him out with a body without lengthy prep work beforehand.
As it was, Hermione did not want to see Tom in the real world right now.
Her hair was sparking as she tore into her dorm room in a flurry of fury, yanking out the diary, grabbing a quill, and poking it sharply into the pages.
Hello Tom, she wrote. Free for a visit?
For you, always, Tom wrote back. Welcome back.
As Hermione's vision changed and she fell topsy-turvy into her own mindscape, Hermione grimly wondered if Tom was prepared for the fury she was about to unleash.
"Tom!" Hermione screeched. "Tom, come out!"
She watched as Tom came out from behind a rock face in the hellish fire of her mindscape. He looked surprised and alarmed.
"What is it?" he asked. "You sound upset, Hermione."
He wasn't wrong; Hermione couldn't remember ever feeling so incensed and furious before in her life.
"Sit down," she snarled at him, indicating the opposite bank of the lava river. Tom hesitated, and Hermione glared. "Sit down."
Warily, Tom did so.
"I have had a revelation," she said, gritting her teeth, "that I am desperately hoping you can disclaim and disprove."
Tom looked at her, holding up his hands in innocence. "I don't know why your ire is directed at me, but I'll help however I can."
Hermione took a very deep breath, closing her eyes and breathing it out. She repeated this several more times, trying to drain enough of her anger so she could think more clearly and find the right words.
"I need to know," she said, "what the ritual to make a horcrux consists of."
Tom froze.
"What?" his voice was incredulous. "Hermione, you can't—that's very Dark magic—"
"The Darkest ritual known to mankind, to be precise," Hermione said succinctly. "The supreme act of evil and the worst of the Dark Arts. So Dark that even Dark Arts texts refuse to describe it – 'of the Horcrux, wickest of magical inventions, we shall not speak nor give direction'—"
"You've read Magick Moste Evil?" Tom cut in.
"But what is the worst act of evil, Tom?" Hermione's eyes flashed. "What is the most supreme evil act?"
Tom looked unsettled, but Hermione didn't stop.
"I thought it was killing someone," she said, laughing. "Killing someone! As if instructions on how to kill a person aren't documented in dozens of different ways in dozens of different places! I was so naïve." She shook her head, disbelieving, before looking up at Tom, her eyes slitted. "But it's not just killing someone, is it, Tom?"
Tom watched her with wary eyes.
"I know enough about rituals and ritual structure to know roughly how they work," Hermione said, her voice dark. "I know that for larger rituals that require fundamental changes of nature, a sacrifice is required, of approximately equal nature to what is to be gained." She held up a hand, ticking examples off on her fingers. "I did a conception ritual to force ovulation, and I had to sacrifice a womb of unborn rabbits to do so. I gained Parseltongue, and a snake lost its life so I could speak its language. At the equinox ritual, a village sacrificed their blood so they might feel the earth's life and magic within them."
Her chest felt like it was heaving, so hard was it to breathe evenly and keep her voice straight.
"But what sort of sacrifice, Tom, is appropriate for a ritual to split and store a person's soul?" she said dangerously. "What could possibly come close to the cost for such a Dark ritual, one that not only goes against nature, but trespasses against the very nature of life itself?"
Tom didn't say anything. Hermione glared at him.
"What is it, Tom?" she whispered. "Tell me, or I will destroy you."
Tom looked at her, wordless.
"It's a soul," she whispered. "It's a soul, isn't it?"
Tom just sat and looked at her for a long, long moment. Hermione watched until he finally responded, eyes meeting hers in resignation.
"…yes."
Hermione saw red, and the next thing she knew, she was screaming.
The world was storming around her, her mindscape a furious rage matching her own. The harsh winds of fire picked up, blowing around her in a whirlwind gale, but Hermione scarcely noticed as she screamed her fury, storming around the bank of the river, furious beyond measure as she stamped her boots down.
"I knew it!" she shrieked. "I knew it, I knew it, I knew it! God damn you, Tom! God damn you!"
Tom watched warily from his side of the river, apprehensive. For one impulsive moment, Hermione had the strong urge to cross over to his side and bash his head open against the rocks; but even in her fury, though, she wasn't that stupid – he'd be able to possess her in moments if he got his hands on her here.
"I hoped I was wrong!" she shouted at him. "God, I'm such a fool! I was hoping you'd be horrified, assure me no, it was some other thing that needed sacrificed. But I think I knew," she said, crying and laughing sardonically at the same time. "I think once I heard it could be done, I knew." She looked at him, furious eyes holding his. "I just didn't want it to be true."
Tom looked at her quietly, and Hermione glared at him.
"You're so much worse than I ever realized," she spat. "Murder – somehow, I could forgive you murder. I could understand it, I could rationalize it. But you sacrificed someone's soul to make this horrid thing." She shuddered. "Tom, you sacrificed their soul."
Tom's voice was steady, resigned. "I did."
"Who?" Hermione wanted to know. "Who did you hate so much that you wanted to destroy their soul?" She paused. "Was it your father?"
Tom seemed resigned to answering her questions. Now that she knew the truth, he seemed to affect a neutral veneer of emotionlessness, not reacting strongly to her goading one way or the other.
"I'd already killed my father by then," Tom said flatly. "I killed him and his parents the summer between fifth and sixth year. I had heard of horcruxes at that point, but I didn't know the details yet. I wouldn't have used him anyway, if I had known – a muggle soul might not have worked."
"Then who?" Hermione demanded.
"Cygnus Black," Tom told her.
Hermione blinked.
"Who," she demanded, "is Cygnus Black?"
"Cygnus Black was one of the patriarchs of the Black family, though from a branch family," Tom said. His eyes glittered. "He was grandfather to Walburga Black, who was one of the meanest, most horrid people I've ever known. She was ruthless toward me when I entered Slytherin, the biggest snob and worst blood purist you could ever imagine."
Hermione stared. She wasn't following the logic.
"So you killed her grandfather?" Hermione said, incredulous. "Instead of her?"
"Myrtle had already died," Tom said. "I couldn't have another student death around me. Cygnus was easier – he was Dark, he taught his children cruelty and lies, and it would upset Walburga." His eyes gleamed. "Plus, he was from a Noble and Most Ancient House. If the sacrifice determined the strength of the ritual's result, I wanted to use a wizard with a well-established and powerful bloodline."
"Even though your own birth disproved blood purism and bloodline elitism?" Hermione said pointedly.
Tom inclined his head. "All the same."
Hermione was shaking her head. "I can't believe this. You didn't even know the man. And you destroyed his soul…"
"That made it easier," Tom told her. His eyes were dark. "I did it during the school year, right before winter exams my 6th year, so Walburga would hear the news and fail her tests." He was lost in reflection. "It… it was pain like nothing I've ever known, the feeling of tearing my soul in half as his soul was erased away… pain that I'll never know again, now, despite my plans." He gestured down at himself. "I hardly realized the result of making a horcrux would be this."
Eternal conscious awareness and imprisonment alone in book wasn't an adequate punishment for destroying a soul, in Hermione's opinion, but it was a goods start.
"And Voldemort has made five horcruxes," Hermione said, shaking her head. "Five souls sacrificed, gone forever, so he could live without dying." She looked at Tom suspiciously. "How did Harry end up with a soul fragment in his brain, then? If he still has his soul?"
"You said the curse rebounded on Voldemort," Tom said. "I suspect some small part of his remaining soul was sacrificed, while some small shard latched onto Harry." He paused. "I suspect that the smaller amount of soul one has left to split in half, the lesser the sacrifice to split it would be."
"Oh, so it's okay now because you only have to sacrifice half of someone's soul?" Hermione spat. "What would that even be? Half a ghost wandering around the afterlife, confused and lost…"
"It's just a theory," Tom told her, annoyed. "Voldemort probably sacrificed the entire soul each time he made a horcrux purposefully. He would have no reason not to, having already murdered the people. It's not like he'd want to leave half a ghost lingering around to testify against him."
Hermione looked at Tom steadily.
"This is the most evil thing I have ever heard of, Tom," she said.
"Yes," Tom said. "I'm not surprised."
She looked at him flatly.
"I feel like I'm morally obligated to destroy you, now, you know," she said. "Now that I know the truth."
"And become a destroyer of souls yourself?" Tom said quickly. "That's a bit Darker than the usual eye-for-an-eye form of justice."
"There are things people are morally obligated to fight against," Hermione insisted. "Dark creatures who destroy people's souls are one of those."
"Dark creatures?" Tom leapt on her comment. "Like what?"
Hermione waved a hand. "Like you. Like dementors. They're the reason I figured this out, learning that they literally eat people's souls."
"So you're morally obligated to destroy all dementors?" Tom said. He raised an eyebrow in challenge. "Just how are you going to do that?"
"I haven't figured that out yet," she snapped. "I got distracted by the revelation of what you had done."
"Allow me to assist you, then," Tom said smoothly. "It was wrong and evil to destroy Cygnus' soul, but it is something I did that cannot be undone. Let my penance be helping you to remove all other creatures that destroy souls."
"What, all the dementors and Voldemort?" Hermione said. Her eyes narrowed. "Do you know how to destroy a dementor, Tom?"
"No." Tom's eyes glittered. "But neither do you. I have a few ideas and theories, and you will need help. I daresay that together, we might have one idea bear out into something resembling success."
Hermione glared at him.
"You are trying for a stay of your execution," she accused.
Tom held his hands up, shrugging. "Wouldn't you?"
Hermione bit her lip. She couldn't really fault him there.
The truth was, she had no idea how to destroy a dementor. She figured it had never been done before. If someone had figured out how to destroy the dementors, there wouldn't be any dementors around anymore - a person wouldn't just destroy one dementor.
It was going to take an incredibly complicated ritual to vanquish a dementor, Hermione imagined. She had no idea how to unmake or counter the magic of a dementor, or what dementors were even made of. So that meant she'd have to capture one dementor on its own to examine, in order to figure out what she would need for the ritual...
Her eyes fixed on Tom, who was waiting silently, hands folded.
"...you have a few theories?" she said finally.
Tom's eyes gleamed in triumph, which Hermione determinedly ignored.
"I do," he confirmed.
Hermione scowled.
"Fine," she said, dragging a hand over her face. "You will agree to help me destroy the dementors, and so long as you are helping me, I will keep your diary." Her eyes held his, flinty. "This does not mean that I think you helping me in any way atones for you destroying a man's soul. This does not mean that I won't destroy you afterward." She glared at him. "Don't mistake this for mercy, Tom."
Despite the fierceness of her words, a slow smirk was twitching on Tom's lips, like he was trying to hide any reaction. It was as if a stay of execution was all he wanted, like he was already sure he'd be able to talk her into sparing him again down the line, and then again, and again. It gave Hermione pause, and a vaguely sinking feeling, but what was she to do? If she was really going to destroy all the dementors, she probably would need significant help.
She bit her lip, watching as the boy across the river of lava considered her words, before giving her a deliberate nod, slightly bowing to her.
"Understood, Hermione," Tom said. His eyes glittered. "I agree to your terms."