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"Mycroft, you don't just give away something for nothing. What do you want in return for this?"

"Truly. Sherlock Holmes, you will expected to assist the Auror office with investigations, just as you do with the normal police."

"Brilliant," Sherlock said.

"Is that what you were talking about earlier?" Harry asked Mycroft, who nodded. Harry's brain started working very quickly. This man was maybe as brilliant as Mycroft Holmes, and he was a Consulting Detective. He took care of really complicated cases, things the normal police couldn't. He had figured out about their world in only about two days, and he could read both himself and Neville easily. "That's more than acceptable," Harry said.

"I only do interesting cases," Sherlock said.

"What, magic isn't interesting enough?" Mycroft asked, but he was joking.

"I'll need books on the subject," Sherlock said.

"Which one?" Mycroft asked.

"All of them, but the most on Care of Magic Creatures, Arithmancy, Runes, Potions, Herbology and Muggle Studies," Sherlock said.

"Why?" Neville asked

"You can't expect me to solve anything when I don't know about the world, can you?" Sherlock asked.

"You'll do fine on your own," Mycroft says with annoyance.

"My books or I'm not doing anything," Sherlock said. "The best ones, the very best Mycroft."

"Yes," Mycroft says, considering what to do next. "You will get your books, and you will have access to the world," he said.

"In exchange?"

"In exchange you will tell no one, no one about the magical world."

"I'll tell John," Sherlock said.

"He's acceptable, necessary if we don't want you trying to dissect a dragon," Mycroft says. Harry looks momentarily mystified. No one would be that crazy, would they? From the glint in Sherlock's eyes, he clearly would be that crazy.

http://www.fanfiction.net/s/8142680/5/