Hi! So this idea has been bugging me for a long time and I finally got around to writing it! As of right now it's only a one-shot but if people want me to I will continue! I hope you enjoy! Review please! :)
Disclaimer: Don't own Sherlock; if I did Moriarty would not be dead.

The coldness. That was the first thing he noticed when he walked out onto the roof. But it wasn't from the weather, no, most of it was coming from the man sitting on the ledge of the rooftop. It was scary, really, how one single man could make him feel so afraid and weak. Of course, he'd never show it. No, he was Sherlock Holmes, he didn't feel things, especially fear or weakness.
He knew-thought-from the moment he stepped out onto the roof that he was going to 'die'. His plan, originally, was to fake his death, take down the rest of Moriarty's web then after however long that took, return to England. But that was before James Moriarty said those two words.
"Join me." It was a statement, not a question. He could tell from the look in the consulting criminals eyes that he was serious. "You got to admit that's sexier."
"And if I don't?"
"I'll burn the heart out of you." It wasn't what Jim had said that frightened Sherlock, it wasn't the look in his eyes, the very same look they held when they had first met at the pool. It was that he was actually considering it that frightened Sherlock the most.
"John.." Sherlock mumbled, his friend's safety coming to mind almost on instant. Could he betray him like that? His first thought was no, but then he remembered Mycroft's words from all those months ago, 'caring is not an advantage.' If he continued to care about John (or anyone for that matter) it would only end with them getting hurt; but if he joined Moriarty he wouldn't have to care about anyone, he'd have no disadvantages, everyone he cared about wouldn't get hurt like they always did.
"He'll be fine. Might be a little mad if he ever finds out but he'll be alive." Moriarty said, pacing around Sherlock, his eyes seeing right through the strong facade he'd been building ever since he was a teen. (Jim knew that Sherlock would join him, they are, after all, each other. Prepared to burn, prepared to do what other people won't.)
"But they'll all stay safe? John? Mrs. Hudson? Lestrade?" He asked, watching as Jim walked up in front of him until they were face to face, only inches apart.
"Of course." Jim answered, as he stared into Sherlock's eyes, icy blue meeting cold, dark brown, "Come on, Sherlock. Wouldn't you like to rule the world? To be in control of everything? To feel powerful? Just the two of us against the rest of the world. Two unstoppable geniuses." Jim was so close to Sherlock now that he felt his breath on his face, "What do you say?" The criminal whispered, as his warm breath danced crossed Sherlock's face again.
All the reasons why he should say no started screaming in Sherlock's mind; if John ever found out he would definitely hate him, there was no question there, but that was if he ever found out, he would be leaving England, of course, going off to cause trouble someplace else, that or they would get new identities, either way, it was more than likely he would never see John or anyone else he cared about again.
The thought about having to murder someone in cold blood also crossed his mind, but he soon remembered what Jim had told him at the pool about not liking to get his hands dirty; there would be people to do any killing that was required, the only part in it he would have in it would be the planning. He also knew that by joining Jim he would become the soul things he tried so hard not to be. A psychopath, a killer, insane. But to be have power..to rule the world, to be able to get whatever he wanted..it would be incredible.
The reasons why he should say no got lower and lower until nothing except the reasons why remained. He'd been on the side of the angles for far too long now, it was no longer exciting-more dull than anything. It was too predicable now, but the side of the devil wasn't. It was mysterious and dangerous and everything Sherlock's ever craved in his life. He wanted to feel the thrill of the chase, the blood running through his veins all the time, not just when he was on a case. And the side of the devil could offer that. He was ready for a change now, he thought to himself and before his head could register what he was saying the word was already out of his mouth and into the cold air, "Okay."