Summary: During her first year at Hogwarts, Ginny Weasley dies… no one notices.
Notes: This depends on Tom Riddle being more cunning than Voldemort, if for no other reason than he's half a soul and Voldemort is far less than that.
Hiding in Plain Sight
It's ridiculously simple to get the girl to open up to him. She tells him about the difficulties of being the youngest child in a family where all her sibling are brothers. He tells her about the orphanage and how no one understood him, what with being the only magical child there. She writes about her insipid little crush on The Boy Who Lived, he writes back about his admiration for one of the most beautiful girls in his house and how she always disdained him for his blood status.
Tom doesn't tell the girl that the other children didn't understand him because he dreamed about killing them even as a child. He doesn't explain that he had no feelings for that pretty girl, save for satisfaction when he caused an 'accident' that left her with a badly scarred face and decreased prospects for marriage all because her lofty attitude annoyed him.
He was Tom Marvolo Riddle. Lord Voldemort. The Heir of Slytherin.
If anyone should be looking down their nose at someone disdainfully, it was him.
He was looking disdainfully at this girl, though. Through the pages of his journal, he watched her grow weaker, pouring more of herself into his pages.
Every action has an equal and opposite reaction, after all. Every time the girl put something of herself into the journal, Tom responded in kind. She told a story; he told a story. Some or her soul leached out into the book… and some of Tom's leached out of the book and into her.
Eventually he was strong enough to possess her, but Tom had no idea to what end. He wanted to open the Chamber of Secrets and unleash the Basilisk. The problem was, Dumbledore would suspect him.
Oh, Dumbledore would have no idea that Tom was a Horcrux, acting through the body of a little red-headed, blood-traitor whelp, but Dumbledore would suspect Tom of having a hand in things nonetheless. Suspicious, nosy old coot. Where others had seen a charming, abused young boy, Dumbledore had glimpsed something far worse and he'd never let Tom forget it.
Aside from alerting Dumbledore to the likely presence of Tom, there were other problems with opening the Chamber.
For one thing, student deaths would lead to the closure of the school and all the students returned home for safety. There was a possibility that the girl's parents would notice the diary, recognize that the magic in it was dark, and alert the Headmaster. Tom's soul-trading with the girl was still tentative at best, for the moment, and he had no doubt that Dumbledore could find a way to reverse it.
If Tom didn't actually kill any students, but merely petrified them instead, the school would likely remain open, though with increasingly tightened security. If he could bide his time long enough… he might be able to thoroughly discredit Dumbledore. The mighty Lord of the Light, getting useless in his old age… can't even protect the children from petrification.
Tom quite liked that idea.
He starts small. Strangling roosters, petrifying a cat, frightening the school with a dramatic proclamation about the Chamber being opened… then he sits back and waits to see what happens. Metaphorically, anyway.
The girl writes to him, worried.
I can't remember where I was that night, Tom, she writes. I was writing to you one moment and then the next I was… somewhere else. The time in between is all missing.
You fell asleep writing to me, he assures her. Sleepwalking is a normal side affect of stress, too. Maybe you're studying too hard and not getting enough sleep? I had a housemate with the same problem; whenever exams came around, he'd fall asleep studying and wake up pacing in front of the fireplace while muttering the answers to his homework.
She accepts his answer too easily, and her fears subside. Then he begins petrifying students.
Eventually the girl begins to suspect him of being somehow related to the petrifications. But by then its too late for her to be rid of him. Oh, she tries. She throws him away, somewhere wet. Tom can feel the water seeping into the binding that holds him.
Then he's picked up by Harry Potter, of all people, and he has a bit of fun at the expense of the oafish Hagrid. But he knows the girl won't dare let Potter keep him and he's only with the boy for a short time before he feels the girl return for him. The bit of him in her lets him know she's near. The bit of her in him lets him feel her frantic fear.
It's intoxicating.
Tom… you didn't tell him anything about me, did you?
Of course not, Ginny. Your secrets are safe with me. If you don't feel like you can trust me, though, I'll understand. I'm not really a person, after all, just a… simulacra based on old memories.
The girl apologizes for throwing him away, guilted into writing to him again by his charming self-deprecation.
You're real to me, Tom.
Really, it was almost too easy.
Finally alone, he stares absently at his hand, opening and closing it in front of his face. The buzz of the girl's thoughts are gone – not suppressed or sleeping, but truly gone – and Tom thinks it will take some getting used to before he's comfortable in this skin.
There was enough of the girl left that he could imitate her mousy demeanor easily enough. Luckily the girl had no close friends who might notice if he slips. The family could be a problem, but… after such a traumatizing event, surely they'd understand if their darling girl needed some time alone or learned to be more assertive. Gryffindors were supposed to be assertive, after all.
Tom smiles, then thinks that he'll need to practice his expressions in a mirror, make sure that he looks like she did in the memories that linger. He needs to look like a happy girl whose smiles meet her eyes, who is warm and open and guileless. He has to look genuine.
No one can know that Ginny Weasley died.
Notes: Originally this was going to show Tom-as-Ginny across several years, but I got stuck and this languished for over a year in my scraps folder. Fished it out today because it looked like a good stand-alone after some polishing. While I don't intend to go beyond this one shot after all, if anyone knows of some good Tom-Became-Ginny fiction or intends to write some, please point it my way. I'd love to read it.