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Sherlock took a deep breath before stepping through the door into the pool. He didn't see anyone, but that was no more than he expected. Slowly making his way forward, his heart thumping with the thrill of the danger, the detective very carefully did not smile just a little bit. Turning and looking for snipers or the like, he just couldn't resist a flare of the dramatic.
"I brought you a little 'getting to know you' present," he declared, waving the USB key for emphasis. "'S what it's all been for, isn't it?" Sherlock, stop smiling. "All your little puzzles, making me dance, all to distract me from this."
Briefly, he wondered if there was any way he could brag about this to John, later. Just as well. The girlfriend was taking up much too much of his doctor's time.
When the door opened, Sherlock was nearly bouncing internally, waiting to see his new "arch enemy".
He did not expect John Watson.
Instantly, Sherlock's brain, which should have begun analyzing the data and coming up with a plan, halted to a grinding stop. This wasn't right. What was John doing there? What?
"Evening," John said with the barest hint of a smile.
No, no, no, Sherlock's brain insisted. This is wrong. John isn't supposed to be here.
"This is a turn up, isn't it, Sherlock?"
The detective wished his brain would just shut up for a moment and let him think. There had to be some harmless, logical explanation to this. There had to be.
"John," he managed, "What the hell-"
Then, John Watson, his friend, started to laugh.
"Oh," he gasped after a bit, "I bet you never saw this coming. You blind idiot."
"But-" Sherlock couldn't form words, "You-"
"I am Moriarty, moron."
"How-"
John tutted at him affectionately, and chuckled. Then, he looked up, frowning. "You seriously didn't get it? After all the hints I gave you? God, and here I was thinking you were clever."
"You're lying," Sherlock stated firmly, "He's making you say this."
"Ugh!" John exclaimed, dragging his hands down his face. "There never was a "he"! He was me! I thought you were so much better than this, Sherlock, really, I did."
"Go on, then," Sherlock said, for the sake of conversation while he worked on remembering how to breathe. "What sort of hints did you give me?"
"You must have picked up on the name, at least!"
"Indulge me."
"Jim Moriarty," John sighed. "I couldn't really go full 'Cruella Devil,' now, could I? But I tried my best. Moriarty, the great Gaelic family, with me being of Scottish heritage, if you'd paid attention. Meaning 'navigator' or something. I don't know, I mostly picked it because it sounded evil. Latin future tense 'I will die' is 'moriar,' and it's something uncommon enough to be distinguishable."
"And 'Jim'?" Sherlock barely whispered, hating the way that everything John said made sense.
"A bit obscure, I'll give you that," John shrugged, "But I would have thought you'd do your research on me. My middle name 'Hamish' is the somewhat more Scottish variation of 'James,' the old version of 'Jim'. Not too complicated, if you're not ordinary. But I guess you are."
"Can I ask just one thing?" he asked, wondering if there was any way this was a lucid dream. "Why are you doing this? Why bother pretending to be my friend when you could just play your games from afar?"
"Because," John said, taking a few steps towards him until he was standing right in front of the detective, "I was bored. Just being a consulting criminal, way too boring. So, I decided to do something a bit risky. Have some fun."
"And playing the soldier and the doctor?"
"Felt like it." Another shrug. "I really can't believe you didn't notice."
"You weren't exactly obvious."
"And you're supposed to be the world's only bloody consulting detective."
There they stood, John staring at him with something akin to disappointment, Sherlock's world falling apart.
"You didn't even notice that I was miraculously away when anything dangerous happened, and just happened to be texting on my phone all day."
Sherlock pursed his lips. "I would have thought that Mycroft-"
"Your brother's almost as much of an idiot as you are," John scoffed. "At least he had the sense to kidnap me."
Sherlock shoved his fists into his pockets. How on earth could he salvage this? Let alone dealing with the loss of his first friend in… ever, but also the pressing matter of containing a criminal mastermind who'd been brilliant enough to play him for months. Sighing ever so slightly, the detective pulled the gun from his pocket.
"Look," he said a little sadly, "I'm going to have to bring you in."
John laughed. "Oh, yeah? How are you planning to do that?"
Sherlock cocked the handgun.
"Seriously? You thought I wouldn't be able to tell a fake gun from a real one? Me?"
"Well," Sherlock said, stuffing the thing away, "I wasn't really expecting you, now, was I?"
"True," John smiled. "It's been fun, Sherlock, really it has. But I'm afraid I'm going to have to go now. You just run back to your brother like a good little boy and tell him what I've done."
"At the risk of sounding cliché," Sherlock managed around the lump in his throat, "You won't get away with this."
"Won't I?" John smirked. He turned and walked away, leaving a crestfallen detective in his wake.
For his everlasting credit, Sherlock managed to wait until the doors closed behind what used to be his friend before he truly fell apart.