A/N: So, here's another chapter. Enjoy it. And, I finally introduced Sam and Dean! (Cas'll show up later!). Sorry for any errors (I literally just finished it moments ago). If you see any, point them out to me!

Disclaimer: I do not own Supernatural, Doctor Who, Sherlock or the Avengers.

Chapter Eight:

Tony pulled himself off his bed, not hastening to open the door despite the now rhythmic knocking. Rory and Bruce didn't even look up from where they were attempting to fix the latter's glasses. He wrenched it open. "What?"

"We need to show you something." John said immediately, walking in and setting down the box he had been carrying.

"We?" Tony glanced at Sherlock, he seemed to be waiting for Tony to take a swing at him. "Fine. It'd better be good."

"It is." John assured him. "C'mon, it'll blow your mind. Sherlock, why don't y-"

"I think you should tell them. I'm getting tired of repeating myself." Sherlock said, stepping inside the room and moving back to the space between the desk and the bookshelf.

"Er, okay. Look, guys, come here." John urged.

"Don't make me read anything." Bruce warned. "I'm kind of short-sighted at the moment."

"Don't worry, Bruce, I'll read it out loud." John said, pulling out a book and turning to the dog-eared page. "Here, look." He pointed to a large, grainy black and white picture, which seemed to have been taken at a distance through a window. "Doesn't he look familiar?"

"Is that the Doctor?" Rory said, leaning closer. "With… President Nixon?"

"Yeah! And it says here 'A few weeks before his sudden and unexplained death, former Secret Service Agent David Jones told me the story of a man who literally appeared out of thin air, in President Nixon's office, saying he was a part of a secret British organisation. He referred to himself as the Doctor and his companions as the Nose, the Legs and Mrs Robinson. After learning of the mysterious child who was constantly phoning President Nixon asking for help, the Doctor agreed to help search for her…'." John stopped, looking up at them excitedly. "This happened in the sixties, but the Doctor isn't a day over thirty, and he hasn't changed a bit!"

"Hey, check out the people with him." Tony said, squinting at the other faces. "That chick looks kind of familiar."

"And that guy kinda looks like my brother, Joseph." Rory added.

"Actually…" Bruce said, taking the book from the three of them and holding it at a distance. "Rory, he looks kind of… like you."

"What?"

"Yeah, like a few years older, maybe." Tony added. "Oh, shit! That chick looks like Amy Pond!"

"What? No way, it is!" Rory exclaimed. "Wow, she looks amazing- I mean, um, for a- an older lady, I suppose."

"Wait, wait." Tony held up his hands. "How did an older Amy and Rory end up in the sixties, nearly thirty years before they were even born, with the Doctor and some mystery lady?"

"It's obvious, isn't it?" Sherlock piped up, sounding annoyingly smug. "He's a time traveller."

Tony turned, glaring at Sherlock. "Time travel is impossible." He replied flatly.

"Then explain the picture." Sherlock challenged.

For a minute, it looked as though Tony might actually explode. He screwed up his eyes, lips twitching violently. "Fine! I can't explain it. But that doesn't mean time travel is real!"

Sherlock just smiled arrogantly at him. "We could go confront the Doctor." John suggested. "If we're lucky he might explain it all."

"He might not even know about the picture yet." Bruce replied.

"Nope, I've made up my mind. Let's go see the Doc." Tony declared, walking out. "Come on, or else I'll never shut that kid up about time travel."

John traded bemused looks with Bruce and Rory, before running after his dark-haired friend. The others were soon close behind them, even Sherlock. As they drew closer to the Doctor's office, they heard muffled moans and whispers. John dragged Tony back, and then crept ahead, close to the wall, pulling out a pocketknife he really shouldn't have. The door to the Doctor's office was ajar, and John could hear bits and pieces of muddled conversation.

"…innocent?"

"…crazy…obviously a d…"

"How…kill him?"

"…salt down his throat."

Gathering his courage, John leapt forwards, pushing the door open with a clatter. The Doctor looked up in alarm and relief, despite the duct tape over his mouth and sealing him to the chair. The two figures turned slowly, one clutching a gun tightly in his hands, and faced John with identical expressions of grim displeasure.

John cleared his throat in surprise. "Dean, Sam… Um, why- why are you torturing the Doctor?"

"Walk away, Watson. This doesn't involve you." Dean ordered.

"Well, you see, it kinda does. I mean, I need him to grade my history homework and give me that 'A' I worked my ass off for." John replied, holding his pocketknife tightly.

Dean smirked. "Look, Watson, you've been a good friend and everything, so I'm going to be honest. This thing isn't the Doctor. John Smith is probably long gone. I mean, haven't you ever wondered why, since this school has been founded, there has been a History professor named John Smith? Why he's always insisted on being called the Doctor? Doesn't that seem a little weird to you?"

"It does." John admitted. "But he isn't… a monster, I don't think. He's a time traveller; an alien from another world."

Sam and Dean let out a derisive chuckle. Dean raised his eyebrows at John, glancing at the others who had crowded into the doorway. "Aliens? Really, Watson?"

"He's a demon." Sam said. "And we need to get rid of him."

"He isn't a demon." Sherlock laughed, stepping into the room. "After all, I should know."

John gasped as Sherlock's eyes blacked over. Sam and Dean both tensed, Sam drawing a knife and holding it out in front of him. The Doctor stilled. Dean advanced, fuming. "You've got five seconds to explain before I gank your ass back to hell."

Sherlock rolled his eyes, back to their regular bluey-greeny assortment. "Would you please not? I'd rather continue existing, no matter how boring it is."

"Four, three-"

"You are annoying." Sherlock said, folding his arms across his chest. "If you must know, I am not possessing anyone. I was invited in."

Dean and Sam traded disbelieving looks. "Who the hell invites a demon in?" Sam asked.

"Someone very desperate. When Sherlock, the real Sherlock, was younger he contracted a deadly disease. There was no cure, no way for him to survive. But Mycroft, his older brother, was desperate. He searched for a way to save his beloved little brother. One day he stumbled upon a spell, a very old spell, which could solve all his problems. And he performed it perfectly. What he didn't realise was that the spell wasn't meant to save mortals. It wasn't a healing spell. It was a binding spell. A dying human body would have its soul removed, hollowed out, and replaced with a demon. The demon would not be able to leave the human body. He would be bound to it until it withered and died. But for Mycroft, his brother's strange behaviour, sudden interest in death and the devil, were nothing of importance. And when his parents threw out the boy, Mycroft took care of him, took custody of him. Because he loved him." Sherlock paused, tilting his head to the side. "A very powerful emotion, isn't it? This love business? It starts with chemicals and signals in the brain, and then it just spreads throughout the body."

"So you're saying this brother of- of the body you're in, let you in because he thought he was healing you- his brother?" Sam queried.

"I suppose so, yes. But the phrase 'let you in' makes it sound as if I wanted this in the first place."

"What do you mean?" Dean frowned.

"Being bound to human flesh is not pleasant. Most demons that go through it are crippled for the rest of their life. And that is the few who survive the process. Quite a few of them go mad. I, however, am rather enjoying the experience, even if it can be painfully boring sometimes. I must admit, I did miss dreaming." Sherlock said idly, picking up something from the Doctor's desk and looking it over.

"You- you can dream?" Sam said.

"Yes. It's much more preferable to the nightmares I had become accustomed to."

Sam lowered his knife uncertainly, glancing to Dean. "What do we do?"

"He's a demon, Sammy. We kill him." Dean replied without taking his eyes off Sherlock.

"But Dean, what if he-"

"What if he's good? Do you not remember what happened with Ru-"

"You said you would never bring that up!"

"I did not! Now do what I say, Sammy!" Dean cocked the shotgun and pointed it square at Sherlock's face.

"No." John said stubbornly, standing in front of Sherlock.

"John, while I thank you for the sentiment, it is unnecessary for you to do that for me." Sherlock said, raising the item he had taken and pressing the button on its side. It emitted a shrill sound that had them all, bar Sherlock and the Doctor, covering their ears and wincing. Sherlock pointed it at the shotgun, which spluttered and fizzled. Lowering the device, he walked calmly to the Doctor's side and untied him.

Dean shook his gun in fury, turning on Sherlock. "You motherfucker! What did you do to my gun!"

"I've removed its capacity to fire." Sherlock said, pocketing the ropes.

The Doctor adjusted his clothes and straightened his bow tie. He ran a hand through his hair and fixed Dean and Sam with a serious look. "That was very rude, you know. You humans seem to have a thing for tying up, well, me."

"What the fuck just happened?" Tony demanded, storming into the room.

"I think you boys had best some inside. We need to talk." The Doctor said, beckoning them in and closing the door behind them.

"About what?" Rory queried.

"About what's happening in the school."