Eep. Yes. Um, I'm not sure whether to blame this on lack of sleep or the fact that I got into a huge argument with my uncle about whether or not Sherlock and John are in love (they so are) right before watching Jekyll.

Also, Moriarty is basically Evil!Sherlock. He's his Hyde. Don't pretend I was the only one thinking it!

Disclaimer: The BBC, Steven Moffat and Mark Gatiss own all the awesomeness that makes up Sherlock and Jekyll. I own nothing.

Sherlock walked slowly into the now familiar pool, gun in one hand, missile plans in the other. He raised the latter into the air, at the perfect angle to be visible from almost every point in the building.

"Brought you a little getting-to-know-you present. Oh, that's what it's all been for, isn't it? All your little puzzles, making me dance. All to distract me from this."

The lights around the edges of the pool flickered for a moment, casting eerie shadows across the unnaturally blue water. Sherlock shivered. He always hated pools; the cloying scent of chlorine, the people crowding around, swimming and laughing and drowning and dying...

A door opened and shut at the opposite end of the pool. "Evening," a familiar voice said. Sherlock's eyes widened, his mind went into overdrive. No, impossible. That voice was stolen, it couldn't possibly belong to who it seemed...

A familiar gangly, long-limbed figure strode over to meet him, shaking its dark, curly hair back out of its eyes. "Sherlock Holmes. I have so been looking forward to meeting you," the figure said.

Sherlock stood, almost paralyzed by shock and fear. The consulting detective, the one and only Sherlock Holmes stood face to face with... himself.

No, he mentally corrected himself, the man across from him was not exactly the same. It was like looking into a mirror and seeing yourself with deliberate mistakes.

This man's eyes were a flat black, he was slightly taller (quite an accomplishment when you consider Sherlock's rather impressive height) and the smile he was currently wearing was twisted, as though he was not used to smiling and wasn't quite sure how to do it.

"Who- who the hell are you?" Sherlock choked out, pulling out John's gun and pointing it at this... thing.

He laughed. "Sherlock, Sherlock, Sherlock. I thought you were supposed to be a genius? All those black-outs, ever since you were, what ten years old? Did you really assume they weren't of any significance? Another side effect of your sociopathic brilliance? Come, come. I expected better."

Sherlock's hands trembled slightly. He wished John could be by his side. "How the hell do you know about the black-outs? Who are you?" he demanded, voice steady.

The man laughed again. It was a cruel, humorless laugh, devoid of any warmth. Sherlock felt a pang as he remembered his own laugh and could hardly hear the difference.

"Tell me, you poor, deprived, misunderstood genius, you ever read Jekyll and Hyde?" he said, grinning at Sherlock. "What?" the shorter man asked weakly.

"You ever read the Strange Case of Dr. Jekyll and Mr. Hyde?" "No. I know the basic premise of the story. What on earth does that have to do with anything?"

The strange man turned on the spot while Sherlock stared at him, keeping his gun trained on him all the while.

"Say hello to your own personal dark side! Of course, I couldn't take the name "Hyde" so unoriginal. Besides, such an unusual name as Sherlock Holmes... I had to live up to that didn't I?" he said, grin still firmly in place.

Sherlock gulped. Yes, gulped. That utterly cliche moment where the villain reveals himself and the hero does nothing but gulp.

"James Moriarty. You like it?' The grin was almost predatory now, flinty eyes boring into Sherlock's. The detective shook his head. "There are a few details I'd like cleared up. Firstly-"

Moriarty rolled his eyes.

"Whenever you black out, my darling Sherlock, I take over. Did you know that we killed little Carl when we were only eleven? He never would stop laughing at you. It made you so awfully upset and we couldn't have that, could we? So, I stopped him. As to our condition, there is a physical change, eyes, height, grin. It's not a split personality. I became Moriarty, I started running London's dark side, sending you little puzzles. Oh, those people strapped to bombs were never really getting the messages from me. I knew everything you would say and everything you would ask and my faithful little pawns sent you all the answers I wrote out. They were all leading you back here, into the recesses of your own mind. Yes, Sherlock, this is all in your head. After all, when I'm not here, I'm only inside your own mind. I could do anything I wanted to you right now. Anything at all. That's everything you wanted to know. And how do I know that? I'm inside your head," he almost sang, looking gleeful.

Suddenly, Moriarty was gone and a certain short, blonde veteran stood in front of Sherlock. "You like this, Sherlock?" Moriarty said in John's voice.

"It's your little pet! He never noticed our "episodes" did he? He believed that you were out on a case, or at the morgue with dear ol' Molly or getting high on some street corner. Ugh. So stupid. Why do you bother, Sherlock? Why do you bother with poor little John Watson?"

Sherlock could hardly see. His vision was blurring and the vision of John's face was overwhelming. "Sleep, 'Lock," John's voice murmured softly.

'Lock? He called him 'Lock. No. No one else is allowed to call him that, no one but John...

"Let me take over. My work is far from done here. After all, I want to get to know our... flatmate."

The consulting detective fell to his knees, dropping his gun and clutching his head in his hands. It was like drugs, overpowering his mind, making it dull and foggy. "Stay away," Sherlock said, trying to sound forceful. "You stay... away from... John..."

"Oh don't you worry," Moriarty's deep, smooth voice spoke again.

"I do have my moments."

Yes. You can see why this had to be written. The idea of two Sherlocks? Extremely enjoyable *cough* Review?