Full Summary/Author's Note/Disclaimer: So, I've been reading fanfiction like most obsessed fans, and I rather enjoyed the idea of Sherlock teaching at Hogwarts. Quite amusing, in fact to the point where I decided to write my own fanfic, despite my withdrawal from fanfic writing a year ago I think (btw the followers of my other fanfic, sorry, but I think the next update won't be for a while...), basically inserting Sherlock into the plot of the Chamber of Secrets and see how he interacts/influences the other characters.
Basically, this is for entertainment purposes only, so I don't own BBC Sherlock or Harry Potter. I couldn't possibly come up with such golden lines/dialogue.
Please refrain from flames, I prefer reason and suggestion. Please don't mention grammar mistakes, for I doubt I'd be able to spot those minor details. Please mention if there's a typo, though.
I know that Sherlock's in the 21st century and Harry Potter's a century ago, but think of this as an AU - as an evil author I twisted time to transport HP's world into this time era, though apparently technology in Hogwarts is still stuck far back in time.
This will hopefully take six chapters, give or take, for I doubt I'd be able to have the motivation to finish a long fic if I tried.
Thank you ever so much for reading, don't forget to review, and enjoy!

The Worst Deal

"I assume you understand why I invited you here," Professor Dumbledore said, lacing his fingers together and resting his hands upon his desk. To his right, Fawkes let out a soft cry and began to preen.

The dark-haired man sitting across from him sat back comfortably in the chair, his dark coat and scarf draped elegantly over its back, his blue-gray eyes gazing intently at the headmaster. "My debt."

Dumbledore nodded. "Once again, the position for the Defense Against the Dark Arts teacher is available. However, only one person applied due to the... unfortunate fates of the previous teachers, and I -"

"Found Gilderoy Lockhart unqualified, and now you're appealing to me to take up the position as the way of repaying my debt. No."

Dumbledore blinked at Sherlock Holmes, and then peered at him closely through his half-moon spectacles. "Might I ask...?"

"How I knew that, or why I won't take the offer?"

"Both, if you don't mind answering."

"I met Gilderoy not too long ago at his book signings, as I was interested in how a man who doesn't leave his home without his hair in perfect condition was capable of dealing with certain creatures, and was appalled at his inability to answer simple questions about said creatures. Thus I deemed him a fraud.

"I could smell his distinct cologne once I entered this room, therefore he must had held a meeting with you not too long before you called me here. He wouldn't had met with you for a reason other than applying for the position you just mentioned, for he would rather be in front of the press or his mirror.

"As he had been reading the Daily Prophet, which I deduced from the streaked stains upon his fingers from when I shook his hand, for hesigns in such a way that his skin wouldn't be marked by the ink, therefore they must had come from clutching a newspaper - far too careful about his appearance - where I noticed beforehand your ad, which had the noted job description. He read the newspaper, saw said ad, and came for an interview.

"As I said before, he is clearly unqualified due to his lack of knowledge or sense. As you said, only one person would apply because of the unfortunate fates of the previous teachers - as the man shows an oversized ego and idiocity, it's so far so obvious that he would be the only one to apply.

"I owe you for assisting me in the elimination of Moriarty's network, not to mention the man himself, and so after a couple of months without word and a few of weeks before the usual start of school, you invite me to your office. This means you have found a way for me to repay my debt, and that is for me to fill this position."

There was a moment of silence as Sherlock finished explaining his deductions and reasoning. Dumbledore studied the man carefully. He remembered teaching the former Ravenclaw - at Hogwarts Sherlock had an incredible intellect and thirst for knowledge, always reading book after book in the library, even venturing into the Restricted Section for them. However, the boy was friendless, easily bored, often sullen, and sometimes slacking off on homework. The Holmes family was an old wizarding family, and after growing up in the magical world, Sherlock found the Muggle world far more interesting, with crimes that bore oddities Muggles couldn't solve themselves. After seeking help from his squib older brother Mycroft (who, with a strong position in the Muggle government, was an invaluable link and help to the Ministry of Magic), he put away his wand and lived among Muggles as their only consulting detective, solving their puzzles and learning their technology, for their sciences were constantly expanding with new things to learn and experiment, despite the frequent stupid Muggle.

After many years of teaching, then adopting the post as headmaster, Dumbledore hadn't heard a word of the intelligent wizard who left for the Muggle world until he showed up at his doorstep, having recently faked his death and desperate to protect the ones he cared for. Three years later with great success, they agreed that Sherlock would have to do Dumbledore a favor in the future.

And now, Dumbledore still found himself impressed by the abilities of Sherlock's mind - all the more reason to hope the man would agree.

"Why are you reluctant to accept the post?" Dumbledore said quietly, seeing that Sherlock had fallen silent.

Sherlock huffed. "For one, I would rather be helping the slow-witted officers of Scotland Yard than attempting to teach mindless children how to tell a hex from a jinx. I doubt my patience would last. Thank you very much, I'll take the next favor."

He gave Dumbledore a false, tight-lipped smile as he prepared to rise.

"So you say. However I strongly believe you would be able to pass on more information than Mr. Lockhart," Dumbledore said.

"I'm flattered."

"Sherlock, I must insist. There is no other favor I would rather you take."

Sherlock slowly let out a breath and squinted at Dumbledore as if determined to deduce him further. "Are you sure?"

"Harry Potter will be returning for his second year at Hogwarts - the boy whom Voldemort is after. Last year Harry was nearly killed by him - I have no doubt Voldemort will attempt at the deed again. I may need your help protecting him and keeping an eye on suspicious events," Dumbledore said gravely. "And yes, I am absolutely sure."

There was silence in the room. Finally, Sherlock said, "Can I bring John?"

"Who?"

"John, my John - erm, my blogger - um, friend." Sherlock cleared his throat and looked over to the side awkwardly. "See, he didn't take it quite well that I faked my death and didn't say so for three years, and won't leave me alone for longer than an hour. I only managed to Apparate at your message from the flat because he was out getting milk. I greatly doubt I can vanish - again - for a school year without him never letting me hear the end of it."

"Is he a Muggle?"

"Yes."

Dumbledore was quiet for a few moments. "I suppose you won't come otherwise."

"Nope."

"I also suppose that you'll come up with a loophole in the rules and bring him anyway."

Sherlock gave him a duh look.

"I hope I'll be seeing you on the first of September at Hogwarts, then," Dumbledore said, rising and extending a hand.

It was only after a few moments of Sherlock's intense concentration on the decision before he shook Dumbledore's hand to close the deal. "One more thing, though" he said with a smirk. "I am not wearing robes."