Hey guys, so I got this idea from a gifset on Tumblr, and although I have another story going on, this seemed like such a good idea, so I had to write it down. Reviews are more than welcome, thank you :)

Disclaimer: I don't own Sherlock or Supernatural

It was a rainy November morning, and John Watson was pouring tea into his mug, when his flatmate and bestfriend, Sherlock Holmes came in the kitchen.
"Morning, Sherlock." he said, with a cheerful voice. He was happy that morning, for some reason.
"Morning," Sherlock muttered. "Do we have any tea left?"
"Yep, in the kettle."

He left the kitchen and turned the tv on, then Sherlock came in and sat down next to him.
"John," he said. "Can you run fast?"
"I… think. Why are you asking?"

He put on a weird smile, then he blinked, and his eyes went all black. Pitch black, nothing but black. John jumped in his seat and stood up immediately.

"Sherlock, what's wrong with your eyes?"
"I'm sorry but Mr. Holmes can't speak to you right now."
"What?" he was confused, then he heard the sound of their door probably breaking into two pieces.
"What the hell…" he murmured, and a second later, two people were standing in front of their door.

The taller one had a gun in his hand, and the shorter one was holding a sharp knife, and a huge sack.
"Oh," said Sherlock. "And I suppose… you're the Winchesters, right?"

The shorter guy turned to John and quickly said,
"Hey, I'm Dean and this is Sam, you don't happen to have a Devil's Trap around here, do you?"
"A what?" John said with confusion.
"Okay Sammy," said Dean. "Seems we have to do this alone."
"Or not," said Sam and turned to John again.
"Can you help us with something?"
"If you explain what is going on to me,"
"Okay how about this? You do the same thing we do and then we explain? Your life could depend on this."
"Um.. okay…" John said, puzzled.

Then Sam walked to Sherlock, with a creepy look, and all of a sudden he punched Sherlock in the face. Dean gestured John to help Sam, while he took a chalk from his pocket and started drawing a circle on the ground. John wanted to help, but Sam looked like he was doing alright by himself. After a minute of fighting between Sam and Sherlock, Dean yelled.

"Okay Sammy, now!"
Sam pushed Sherlock and he got inside the circle Dean just drew.

"That was so easy," Dean laughed. "Didn't anyone teach you how to fight?"
"I know why you're here," said Sherlock with a sick laugh.
"Okay now tell me, what is going on here?" John was about to explode.
"Sam, stay here." Dean said as he grabbed John by the arm and dragged him to the kitchen.

"Who are you? What's wrong with Sherlock and what do you want?"
"Okay, look, relax. I'm gonna tell you everything. But you have to know this one thing first, that guy in there, is not who you think he is. There's a demon inside him."
"Hold on, wait, a what?"
"A demon. They can possess people, get into them. And right now, there's a demon inside him. Is he your friend?"
"Yes. But what will you do?"
"The demon inside him is really important to us, we're searching for another demon and he might know where he is."
"How are you gonna get the demon out?"
"We won't, not for know. Look, I understand he is your friend. But we have to get information and this could be our only shot-"
"How are you going to do that?" John was beginning to realize that whatever these men were talking about, could hurt Sherlock.
"We're gonna start with basics."
"What are basics? What do you mean start?"

But Dean was headed to the living room again, John followed.
"We know you work for Crowley." Dean said.
"And?" said Sherlock coldly.
"We wanna know where he is."
"Like I'm telling you."
"Of course you are," said Sam with a cold grin on his face. "Look what we have here," he said, taking the sack and showing what's inside of them to Sherlock.
"Bones?" asked John.
"That's just a rumour, wouldn't work."
"Well, let's see."

Sam took a lighter and a second after John realized he was going to burn the bones, the demon smirked.
"I guess I can let you speak to Mr. Holmes for a couple minutes, then? Considering this will be the last time you'll ever see him."
"What?" John was so confused and kind of scared now.

The demon blinked again and his eyes were back to normal, he stumbled for a second, losing his balance. After a moment, he was looking at the two strangers and John with confusion. That was new for Sherlock.

"Will one of you tell me what exactly is inside me?"
"Okay, here we go." said Sam.
"Wait, can you feel him?" asked Dean.
"Yeah, he's hiding. I didn't take over, he let me."
"That can't be good." said John.

After explaining everything to Sherlock, he looked really calm.
"What exactly will happen when those bones are burned?"
"They're the bones of his previous body, his original body. Michael Green. When it's burned, he burns too. That way he can tell us something."
"But when he's burning… I will also burn?" Sherlock was unexpectedly calm.

Nobody answered him.
"I will also burn, won't I?"
"Yes," said Sam with a low voice.
"No," said John Watson. "No, there's no way. No way."
"Do you do this for a living?" Sherlock asked curiously.
"You could say that."
"Wait, you kill people to get information… from demons. Did I get that right?" John was getting pissed.
"This is important, we're trying to stop something huge here."
"You are not going to kill anyone, not today." said John.
"You're gonna stop us?"
"I've had military training, I know 22 ways to kill people with my bare hands."
"Look, okay, we're gonna try this the other way. Relax."
"I'm getting bored of this," said Sherlock with a cold voice, and when everyone turned back they saw that the demon had taken control again.
"Let's make a deal." said Sam. "You tell us where Crowley is, we let you go."
"Yeah, right, then Crowley finds me and kills me, what's the difference? I'm dying today anyway, but I'm taking this babyface with me."
"Dean, maybe we can try exorcism." whispered Sam to his brother.
"Then we have to find another demon close to Crowley, that could take ages, and you know that."
"We can't kill an innocent man."
"Sam, I understand, but we did this a million times. I mean, what do you think happens to those people?"
"If only I could still kill them with my mind, then this man would live."
"Don't get me started on that, Sam."

John Watson was growing impatient and as the Winchester brothers were discussing, he stared at Sherlock.
"Watson, right? John Watson." said the demon. It was horrible, seeing Sherlock that cold and that evil. He didn't answer.
"I can see his mind, you know. He's fighting to regain control over this body. Too bad. He won't. This is your last time looking at his face, so go on, stare."
"You're not going to kill him." John said.
"No, but they will." He pointed to the brothers. "You know what, I like you. I could actually get out of him, but you see… Devil's Trap. If there was a tiny, tiny hole on this…"

John was beginning to understand what he meant, but he was a demon after all. Then he saw the Winchesters still discussing, and Sam was staring at his eyes, almost sorry for him. Would they actually kill an innocent man for information? He was so confused now, and he was torn apart between letting the demon out and leaving it to the Winchesters. But either way, Sherlock could die and it would be his fault. He closed his eyes and thought.

"I'm sorry, John. But we have to do this."
John's eyes widened with fear.
"No, you can't. Can't you see that he's not gonna tell you anything?"
"Then we still have to kill him."
"Can't you kill him without hurting Sherlock?"
"We can only exorcise him, but then we'd be letting him go."
"Then let him go!" John yelled.
"Look, John, you don't understand. We can't. You don't know how important this is."
"The only important thing here is Sherlock, to me."

Dean sighed.
"If it was your brother, Dean. Would you kill him?"

Dean had nothing to say this time.
"If you dont exorcise him, or whatever, I'll ruin the circle and he'll go. This is chalk, after all. Not that hard to wipe away from the ground."
"Oh, boy." Sam gave a sigh.

Sherlock was grinning all this time.
"Then I guess we have no choice." said Sam, finally. "We can't kill a person, we can't."
"We've done this before." said Dean.
"I'm not arguing, Dean." He started saying words- probably in Latin.

Sherlock started to shake and Sam started saying words even louder. John was panicking but Dean gestured him to relax. After a moment, a black smoke came out of screaming Sherlock and then he fell to the ground, John quickly ran to him.

"He's gonna be fine," Dean said. "I guess we're leaving now."
"Yeah, hey, wait," John got up again and stood next to the Winchesters. "Thanks, for everything. I don't know what would I do with him if you didn't show up."
"Yeah don't mention it," said Sam with an uneasy smile and they just walked out of the door, as if nothing happened. John rushed to Sherlock again, helped him to the couch and stood near him, with a worried look on his face.

"Don't look at me like that," Sherlock said with an annoying voice.
"You do realize what just happened, right?"
"Yeah, of course I do. Let me tell you something, though. He was so scared, like, really scared that those guys might kill him. I'm just thinking… Maybe they didn't do the right thing, letting him go."
"They were going to kill you, too."
"I know."
"You are unbelievable."

After a couple minutes, Sherlock looked at John.
"John, thanks."
"What for?"
"For not giving up on me. Anyone would freak out, you didn't. And they didn't kill me because of you, so… Thanks."
"It's fine, Sherlock. I've got the nerves of steel."

Okay I realize it's not that good. But thank you if you read this and reviews make me happy :)