Chronologically this story happens some time after season 5.
A Tortured Soul.
He was tired and hopeless. In the distance he saw a light in a house by a junkyard. Someone had to help him. It was his last hope. He was surprised that he could even move at all. It was just a little bit further. He was a nondescript man usually. But as Sam opened the door he saw a man beaten to the pulp and barely limping.
Sam, Dean, and Bobby had been celebrating their latest hunt and having some drinks that night. Then there was a knock on the door. When he opened it Sam was stunted, but let the stranger in. Bobby and Dean looked at each other bewildered.
The injured man smiled and then winced in pain. Bobby offered to call 911, but the man refused. "I can't. Please just let me spend the night and then call me a cab in the morning."
Dean nodded. It was better not to bring police attention to the house. "Let me get you something for your wounds." The man thanked him and asked if he could wash up first. Bobby agreed. The men didn't know what to make of this situation.
He looked much better after washing his wounds. That is, he didn't look half dead anymore. His injuries were extensive and he hadn't noticed before how botched his makeshift surgery was. He was missing a kidney, a lot of blood, and God knows what else. He limped into the kitchen and asked for painkillers. The only thing left in Bobby's kitchen was a half empty bottle of Jack. The man drank it and tried to sew his wound by himself, but couldn't. Sam offered to help. When it was finished the boys asked the stranger for his name. The man avoided the question and thanked them again for their kindness. He said he was attacked, but that he had trouble with the law and couldn't risk calling the police. He was attacked by a cop whose eyes inexplicably turned black and who charged at him like crazy. He fought back and ran. The way it looked, he must have killed the police officer.
Sam and Dean looked at each other with understanding. The stranger didn't know about demons and that the cop most likely didn't die. The stranger was lucky to have escaped with his life. Bobby hoped that the demon wouldn't follow the man back to his house.
The stranger winced in pain and asked his host if he had any more booze or pain pills. Bobby only had one more beer left, stashed way in the back of the fridge. It was old and it wouldn't help with the pain much, but it couldn't hurt. The stranger was thankful. He smiled and took a big swig out of the beer. Suddenly he was in more pain than he ever remembered feeling and keeled over on the floor heaving. He had blurry vision as if there was steam all around him.
The boys acted fast. Bobby had forgotten that this was the last bottle with holy water in it. They dragged the weakened stranger to the basement and chained him to a steel chair. The stranger passed out.
When he woke up he looked scared and shocked. Sam started, "So was the story true? Except of course for the part where you left the cop's body and possessed this poor stranger." The man didn't speak. He glanced over at the stash of knives organized in a leather case on a table. He was still in pain and anticipated that by the end of the night he'll be in more pain than he had ever imagined. "Or maybe you just made up the whole story. We know how your kind loves to lie," said Sam.
"My kind? I don't know what this is, but please let me go," replied the stranger shakily.
"You do know what this is," barked Dean, "and you'll tell us who you are and how you found us".
He slid one of the blades over the man's chest. The wound glowed and hurt like hell. The man tried to hold back his scream until it happened again.
"You know, we heard an interesting thing on the police scanner," said Sam. "Apparently there was a small massacre in a warehouse nearby. Now you wouldn't have anything to do with that would you?"
The man just stared at Sam not saying anything. Bobby splashed holy water on the unwanted guest. The stranger hissed. "Let's start with an easy one," said Bobby. "What is your name?"
"I don't know," screamed the stranger painfully. Bobby noticed that this demon didn't have the usual snark.
"He doesn't know Sammy," Dean said with a smirk, "maybe we should help refresh his memory." Dean made a deep cut with his demon knife. The demon had tears streaming down his face, but then he put his head down and took a deep breath. When he lifted up his head and opened his eyes they had turned black. He started chanting something which had the Winchesters worried.
Suddenly, they saw Castiel appear. "Cass?" asked Dean. "What are you doing here?"
"I'm here because I heard a prayer for me," replied Castiel.
"We didn't call you," said Sam. "But we're glad you're here."
The demon was shocked. His mouth was gaping. He prayed, but he didn't expect to see an actual angel. "I called you," he said in a shaky voice. Castiel started walking towards him. "Please don't hurt me," begged the demon. "Please hear me out".
"A demon praying," said Bobby in disbelief. "What kind of tricks are you playing at?"
" 's a first time for everything," said Dean.
"So talk." said Sam to the demon. The men were watching him intently.
"You might not believe me," the demon stammered, "but I don't think I'm human."
"No shit, Sherlock," snarked Dean.
The stranger continued "I was. I mean I think I am a ghost or something. I don't know what I am. The first thing I remember is darkness and then I was floating aimlessly through the sky. When I heard a scream in a nearby warehouse I instinctively knew that I should go over there. I saw a bloody man chained to an operating table and I sort of went into him. Maybe I imagined it. Maybe this is my body and I just passed out and then came back to my body like an astral projection or something. But I don't remember my life as this man. I set myself free", he continued "and fought my way out of there. When I was out, I saw a cop. I managed to knock him out and I ran. When I couldn't run anymore, I walked until I saw a light in the distance. Your house."
"Wow they get more inventive every day", said Bobby in disbelief, "a demon, playing Casper the helpful ghost."
"Why do you keep calling me that?", asked the stranger. "What do you want with me?"
"Perhaps you'll find this helpful", Castiel brought a mirror in front of the chained man. The man gasped in fear when he saw his black eyes. "What the hell is that?" He asked himself.
Castiel took away the mirror.
"Guys," started Sam, "what if he isn't lying? Cass is it possible for a demon to lose its memory?"
"I don't know" said Castiel. "Anything is possible. I've never heard of it. A demon would have to go through something completely traumatizing for its broken soul to be damaged enough to lose its memory like that."
"You mean as in hell isn't traumatizing enough?" asked Dean.
The stranger drifted away from the conversation. He couldn't believe he was chained up and tortured again. They must have put something in his drink. Drugged him somehow to be seeing these hallucinations. What they were saying couldn't be true. He was not a demon. But he knew he was most likely going to die tonight.
Suddenly the lights flickered. There was a sound of a screeching door upstairs. They were not alone. The man felt a flicker of hope, but that faded away soon.
It was the same voice as before calling out for him. "Here, lil' demon… Come out to play… ."
"Please let me go. It's him. The cop. He wants to finish the job," pleaded the tortured demon.
"I knew that idjit would lead It back to my house," said disgruntled Bobby.
"What do we do?" asked Dean.
"I'll take care of it," said Castiel, sure of himself. Castiel disappeared and all of a sudden the men saw a bright flash of light. They ran upstairs and a demon in a cop uniform was grinning while holding his hand over a bloody angel repelling sign.
The demon flung Dean and Bobby across the room and Sam ran downstairs.
"Are you scared little boy?" mocked the Demon.
Sam ran towards the chained up demon and asked "Do you think you can get rid of your buddy?"
"I don't know. I'm not who you think you are. This guy will kill me," he responded.
"Right now you are our only hope," said Sam while unchaining the demon. "You have no choice."
The demon came downstairs and started taunting the other. "Well how's it going stranger? Best be going back to your cage. I think you've played a human enough for one day. And hiding out in a Winchester house… how shameful."
The injured man didn't know what to think. They were all insisting that he was this demon. This couldn't be true. He would know if he was an evil demon from hell. But he had no memory of anything. "Who am I?, he finally asked the demon.
"Woo. You don't remember. Do you?", laughed the other demon. He came close to the injured demon and whispered "Does the name of a God's firstborn ring a bell?"
"Adam?" asked himself the stranger. Then he fell on the floor as he suddenly had a vision of what hell must have been. The incredible pain he felt and the blood and flames covering his body.
In that moment Sam saw Dean standing behind the demon in the cop meat suit and they both attacked in unison. Dean managed to stab it in the shoulder, but it just flung both of the boys across the room again.
It was just demon against demon now.
The amnesiac stared at his enemy. He didn't understand it, but a sudden surge of hate he has never experienced before was focused on this creature. Somehow this demon had been a part of his past suffering. He just knew it. All of a sudden he felt himself leave his body, hover over the stranger, and enter his body.
Sam and Dean lifted their heads and they saw a gray, flickering smoke enter the other demon. In a few seconds of internal struggle they saw the demon spark orange just like many of the demons they've killed before. The body collapsed.
They got up and checked over the first stranger's body. He was still breathing.
Suddenly the cop's body got up. He smiled at them and flashed his black eyes. The boys were stunted. They braced themselves for an attack, but then the demon fixed his shirt and calmly walked upstairs.
The demon walked past Bobby who was just waking up. He tipped his hat and said, "Thanks for the beer. I'm all better now." He then flashed him a smile as he exited the door.
Sam and Dean ran upstairs and Bobby told them the demon's last words. Then they went downstairs to get the passed out stranger.
They weren't sure what to think of what happened tonight. What could be powerful enough to kill another demon like that, they wondered. And why didn't it want the Winchesters dead?
Dean grabbed his car keys. "Help me get him in the car Sam. We gotta drop him off at the hospital."
Sam agreed and helped Dean get the passed out stranger into the car.
"What was this Dean? Demons banishing angels, possessing and killing other demons like that?", asked Sam while they were driving.
"I don't know Sammy," replied Dean. "But whatever it was, it will come back and we gotta prepare ourselves to fight it."
The boys drove off into the night.
Miles away a man in a bloody cop uniform was walking briskly. He had a grin on his face. He knew his name. It was Adam. And the name Winchester was oddly familiar to him. He couldn't put his finger on it, but he felt that he had met them before this night. Eventually he'll figure it out and he'll be back.