If you ignored the magical ceiling, the robes and the hovering ghosts, the Hogwarts Great Hall could be mistaken for any other public school at lunchtime.

Noisy, chaotic, and utterly, irredeemably dull.

In a day and a half of lessons, Sherlock had learned nothing of interest, save for one thing: that magical children were every bit as vacant and uninteresting as Muggles. The only upside was that they were leaving him strictly alone.

For now.

Still, it was best to know your enemies, even if they weren't enemies just yet. He'd found a slender notebook slipped in among his school texts, so he took it out now and began writing.

"Children are seated by house. Inter-house mixing is virtually nonexistent, even among first-years – only the first full day and the herd mentality has already set in. The Slytherins look more loutish than criminal. Too bad. I had expected better from a house full of so-called dark-lords-in-training."

Sherlock had been scribbling away, scarcely looking at the page. He glanced down to see his writing fading away into the thick paper. As he stared, faint markings began to appear and resolved into an elegant cursive script utterly unlike his own.

"I see Hogwarts has changed little since my time. You have my sympathies."

Sherlock blinked twice and then sighed and wrote in the book again.

"This is one of those stupid magical diaries, isn't it."

The words faded immediately when he lifted his pen. More of the loopy cursive appeared on the page.

"I am indeed magical … however 'stupid' is not a word that has been frequently applied to me."

Sherlock rolled his eyes.

"There was a whole shelf of them at Flourish & Blotts," he scribbled. 'Love troubles? 'Fess up! Our enchanted journals will listen… and never tell.' I was impressed at first - embedding a consciousness within an inanimate object would be a very intriguing bit of magic. But I did a few experiments, and worked out that the diaries can't actually think – they're charmed to interpret language and simulate typical social interactions. And then I got thrown out of Flourish & Blotts for vandalizing the merchandise – honestly, it's a journal, it's meant to be written in, I didn't even use ink - "

"You seem distinctly unimpressed."

"They simulate typical social interactions." Sherlock underlined the last three words for emphasis. "I don't socialize. And I am certainly not typical."

"You find ordinary people dull. You're isolated because none of your peers can match your intelligence."

"So far so obvious. Am I supposed to be surprised?"

"You've never wished for someone to talk to? Someone who understood?"

Sherlock paused, his pen hovering over the page. Then he snorted.

"Do you have any idea how utterly stupid the average person is?" He paused. "Don't bother answering that. And people with magic seem to see it as an excuse to discard what little intelligence they have. A notebook designed to recreate what passes for conversation among wizards would be…beyond useless to me."

There was no response. Sherlock sighed. He'd have to use small words or the thing would overload like a computer running DOS.

"You don't have a mind of your own. You are probably even more stupid than a normal human. You also erase everything I write, which sort of defeats the purpose of a notebook. So I'm going to get rid of you."

The response came quickly. The writing was as neat as ever, but it seemed somehow irritated.

"What a charming fellow you are. You must be tremendously popular."

Sherlock narrowed his eyes. The thing was sarcastic and forgetful."

"Popular? You just said I was isolated."

"One can be liked by all while trusting no one. And with your delightful disposition, I imagine the other children flock to you."

Sherlock scowled. Stupid thing - no wonder T.M. Riddle had gotten rid of it.

"I'm going to leave the diary where one of the first-year girls will pick it up," he wrote, rather spitefully. "I'm sure they'd like a sympathetic audience for their…thoughts, such as they are." He glanced around. Over at the Gryffindor table, a tiny redhead was poking at her chicken and gazing longingly at the Potter boy. Perfect.

He began to close the diary, when the message appeared in an urgent scrawl.

"WAIT"

He paused. More words appeared, neater, but still hurried.

"This is an artefact of great power. Would you cast it away so carelessly?"

"Well, T. M. Riddle obviously did. I wonder why?" Sherlock smirked. "Maybe he wanted to actually reread things after he wrote them."

After his words had faded, the page remained blank for a few moments, like a hesitation. And then –

"I…am T.M. Riddle."

Hours had passed, and still there was no reply. Tom cursed his own stupidity. He had intended to begin gently, gain the child's trust while divulging little of himself. He hadn't intended to blurt out his identity, and he certainly hadn't planned to get into a quarrel like an ignorant schoolboy. He ought to have better control.

(But that little idiot was just begging for a Cruciatus..!)

The boy - and it was a boy, from the way he spoke about girls – had obviously not grown up with magic. The strange jargon, the mentions of 'normal humans' and 'wizards' as if they were separate (any wizarding child would know that Muggles were the anomaly, filthy, unmagical creatures that they were). How the devil had his diary fallen into the hands of a mudblood?

Still, there was no denying that the boy was clever. Brilliant even, with a nice, promising hint of disdain for his peers. He would not be as easy to manipulate as Tom had hoped – but perhaps he wouldn't need much manipulating at all. Tom smiled (a decidedly queer experience, since he had no face or lips) and reflected that his tedious non-existence might soon become less so. Why, this might even be fun. Unless…

Unless the little fool went and fobbed him off on some snivelling Hufflepuff!

Damn it all.

Hours passed. Tom raged and fumed and finally resigned himself to a life as the diary of a preadolescent girl. Suddenly, words began to appear on the inside front cover of his diary, underneath his own inscription.

W. S. S. Holmes. Tom felt a surge of triumph. He absorbed the ink – nasty Muggle-made stuff – and printed his reply.

"A pleasure, Mr. Holmes. Have you decided to keep me, then?"

"Hardly. It was an experiment." What? Like those Muggle idiots in white coats, poking at rats? What the devil was the boy talking about?

"Please do enlighten me," he responded.

"I've never heard of any sort of magic that allows a human consciousness to enter an inanimate object. It seemed more likely that an ordinary enchanted diary became damaged, giving nonsensical responses."

"You write 'seemed', past tense. Have you changed your mind?"

"The enchantments on the diary make everything I write disappear. But T.M. Riddle was able to write his name – "

"And so you inferred that T.M. Riddle – that's Tom, by the way, pleased to meet you – began with an ordinary notebook and wrote his name before the enchantments were placed. Excellent reasoning, Mr. Holmes."

"That's still not proof that you are Riddle, though. He might have charmed the diary to pretend to be him, though I can't imagine why. Though perhaps he didn't mean to, perhaps he meant to do something else and mucked it up - ."

"Still, it bears investigating, does it not? I seem to recall that a Ravenclaw never refuses a good mystery."

There was a pause. Riddle sensed the pen hovering over the page. (No ink splatters, though – no doubt the little Mudblood was using one of those newfangled ballpoint contraptions.)

"I never told you I was in Ravenclaw. Am I supposed to be impressed that you worked it out?"

"I couldn't possibly hope to impress someone as clever as you," Tom returned, rolling his nonexistent eyes. Arrogant little sod.

"You could be bluffing. It's what I would do. Out of all the houses, Ravenclaw is the only safe guess because everyone wants people to think they're clever. So either you'd be right and I'd be impressed, or you'd be wrong and I'd be flattered."

"You give me too much credit, my dear boy. Surely such a scheme would be beyond me." Tom paused, tasting victory. "I am, after all, a malfunctioning enchanted diary with no mind of my own."

There was no response. Tom felt that this time the silence was a victory – as if he'd dealt a blow that could not easily be countered. He felt a warm glow of pleasure, and thought nostalgically of his first time casting the Cruciatus.

Eventually, Sherlock would fall. Given time, Tom would break his mind and bend the Mudblood to his will. But in the meantime…In the meantime, things just might get interesting.

Sherlock closed the diary, a small smile on his face. He was by no means convinced that there was truly a human mind trapped within, but Tom was right – it did bear investigating. Oh, there was so much to do – he'd have to dig up every detail on Tom

Slipping the diary into his satchel, Sherlock felt his smile widen. He might have to sit through endless redundant lessons and write reams of dreary essays, but at least he had a halfway decent mystery to solve.

Things were about to get interesting.