Author's Note: This is Part 1 of my The Monster That You Know series. The basic concept-Dean died as a child, and John replaced him with a shifter kid-was inspired by darkskinwalker's "But I'm the One You Know" on AO3, though our stories are very different.

Chapter 1

I stirred awake at the sound of the door to our motel room closing. I'd had a difficult time falling asleep tonight, the ibuprofen taking longer than usual to counteract the bruising. I turned towards the other bed and sat up abruptly. Dean should have been fast asleep—the painkillers I'd given him after stitching up the wounds from taking down a wendigo earlier should have knocked him out for hours. But his bed was empty, his jeans and boots gone.

I got up, quickly pulled on my own clothes, and threw on my jacket. Force of habit had me slipping my Taurus into my waistband and my silver knife into my jacket pocket. I couldn't count on the fact that Dean hadn't woken me up to assume that nothing was wrong. Even after all this time, my big brother still defaulted to "Keep Sammy safe" mode and tried to put himself between me and any threat. Which is why he had ended badly clawed up this evening while I'd escaped with only a few bruises.

The air was crisp and cold and the parking lot devoid of life when I stepped out of the motel room, the Impala still resting in front of the door. I walked around the side of the building and saw movement in the woods behind the motel. I drew my gun and stealthily approached the tree line. As I crept closer, I saw a small fire built on top of the packed snow and my brother standing beside it, stark naked. I froze in horror as I realized he was pulling off pieces of his skin and throwing them in the fire, eyes gleaming silver in the flickering light.

I jammed the pistol, loaded with useless regular bullets, back in my waistband and pulled out the knife before darting forward. "What the hell have you done with my brother, you bastard?" I shouted, grabbing the shifter by the shoulder and holding the blade against its throat.

The creature turned wide green eyes on me and raised its hands slowly. "Shit! Hold on, Sam! I am your brother, I'm Dean. Let's keep calm and go back to our room. I can explain everything there, I promise."

"I'm not going anywhere with you, asshole! When did you switch with Dean, and where do you have him? Start talking now, or I'm gonna start cutting things off!" I pressed the edge in closer, drawing a thin line of blood.

"Please, Sammy! I haven't done anything, I swear! Listen, I know you're not gonna take my word for it. But I've got proof back in our room, I really do. Just lemme show it to you! After that, if you still wanna use that knife or wan—wanna leave, I'll—I'll understand. But you gotta lemme show you the truth first." Tears now glimmered in its eyes.

I looked down at the monster wearing my brother's likeness. There was no sign of the cunning, rage, or sheer madness I usually saw when dealing with shapeshifters. All I could see in its expression was sorrow and fear.

"Fine. But you stay in front of me, and no sudden moves!"

"All—all right." The shifter took a step back and slowly bent down to pick up its—Dean's—clothes. It kicked dirt and snow over the fire and then walked backed to the motel. It was still nude, fair skin shining in the winter moonlight, familiar constellations of freckles scattered over its shoulders and back.

I tried to tamp down my worry for Dean as we got back to the motel room, hoping that he wasn't in bad shape wherever he was, hoping that this delay wouldn't worsen his situation. I indicated that the shifter should stand still in the middle of the room as I turned on the lights and went to the duffle bag of weapons. I swiftly exchanged the clip of standard bullets for one of silver and grabbed a pair of silver-plated handcuffs.

Once I had my gun trained on it again, I motioned for the shifter to move close enough to slap the cuffs on it. It didn't look happy at being bound but didn't seem to react to the silver. I frowned, recalling that it hadn't flinched when I cut it earlier either.

"What is it you need to show me?" I asked harshly. When it started to go over to Dean's bag, I said, "Hold it! There are all sorts of things in his bag I'm not letting a damn monster get anywhere near. So you stay right there and tell me what to look for."

The shifter sighed. "Okay. There's a pocket sewn into the lining in the bottom of the bag. You'll find a slit in the seam near the end closest to the base of the zipper."

I pulled the bag to me and pushed aside Dean's clothes and other belongings until I reached the seam it had described. I felt around until I found the slit and cautiously reached inside. Something rustled under my fingers, and I pulled out several sheets of creased and folded paper. As I unfolded them, I realized they were pages torn from Dad's journal. I sat down at the dinette table and smoothed open the first page with one hand, still keeping the Taurus aimed at the creature with the other.

November 3, 1983

I can't believe they're both dead. My beautiful Mary, pinned to the ceiling like some kind of bug, her stomach cut open. And the expression on her face before the fire covered her . . . I've never seen so much pain and terror, not even in 'Nam. What could have done that to her? I don't care what the authorities say, there's no way that was an accident or anything remotely "normal!"

And Dean, oh my God, Dean. I handed Sammy to him and told him to take the baby to safety. But I should have followed him, made sure he was safe, instead of trying to get to Mary, who was already dead. I could have stopped him from going back inside to find us, I could have kept him safe. The firefighters found him in the hallway, just a few feet from the nursery. They said it was the smoke, that he was already gone before the fire got to him. It's my fault that my boy, Mary's little angel, is dead.

What am I supposed to do without them? All I have left is Sammy. I have to be strong for him. I have to protect him and find out what killed his mother and caused his brother's death.

I stared at the words in absolute shock. What they said had to be impossible—there's no way Dean had died the same night as our mom! I raised my eyes to the other figure in the room. The shifter had managed to put its jeans back on and now sat on the edge of the closest bed, its head lowered and shoulders slumped. Everything about its appearance was as familiar as my own—tousled dark gold hair, broad solid shoulders, long bowed legs, scarred capable hands. If my brother had really died as a small child, then who was this thing mimicking?

I took a deep breath and looked back at the pages in my hand, hoping to find answers. The next few entries covered the months immediately after the fire, describing the beginnings of Dad's search and early forays into hunting. They were full of expressions of grief and remorse over the deaths of his family but contained nothing about the mystery of what had happened to Dean afterward. A couple more promising entries were dated shortly after what should have been my brother's fifth birthday.

January 28, 1984

Took out a shapeshifter today. Damn thing was killing people, taking their forms to get into their homes, and stealing their valuables. By the time the real bodies were discovered, the shifter would be long gone. It fortunately wasn't much of a fighter and was easy enough to take down. After disposing of the body, I backtracked to its lair to make sure it didn't have any victims trapped there. To my surprise, I found its offspring instead. I thought it was another victim at first, until the kid panicked and shifted in front of me.

I know I should kill the thing. A baby monster is still a monster. But it looks to be about Dean's age, and I was struck by a crazy, wonderful idea. I still have pictures of my boy and even a keepsake box that survived the fire with a lock of his hair and the tooth that got knocked out when he fell off his tricycle. More than enough to allow the shifter kid to do its thing. If I do this, I can have a part of my son back, or at least as close as I'm going to get in this life. And Sammy can have his brother again. He needs someone to take care of him better than I can. The hunt doesn't leave me with much time or energy to look after a baby properly.

So I gave the little shifter a choice. I could send it to join its father wherever dead monsters go, or it could do what I want and take Dean's place. I made it clear that if it ever tried to harm Sam or gave him any reason to think it wasn't really his brother, I would make sure it would take days to die. Sammy can never learn the truth. As far as he will ever know, his brother never died.

January 31, 1984

It's uncanny, how much it resembles my Dean. Not only how it looks, but also how it talks and acts just like him. No one should be able to tell that it's not the real deal.

It's been doing a great job so far of looking after Sam. It hasn't complained once about having to tend to the baby. If I didn't know any better, I'd even say it's genuinely fond of him. And fortunately Sammy has taken to it like gangbusters—for the first time in months he's not crying all the time, and I actually caught him smiling again earlier today. This plan is working out better than I ever expected.

The little creature also seems absurdly grateful for any affection or praise I give it. I have to admit, I'm finding it difficult to remain as hard as I should. And not just because its mimicry of my lost boy is so good. It's a surprisingly endearing little thing, sweet and eager to please. I'm nowhere close to trusting it yet, but it seems like the carrot will be more effective than the stick. Hopefully I can train it right so that it doesn't turn into a monster like its sire.

I've already moved us away from Lawrence. We can't be in contact with anyone there or any of Mary's family, anyone who knows what really happened to Dean. As long as we do that, and as long as the shifter keeps playing its part well, we can be a family again. I can't bring his mother back, but at least Sammy will have his big brother to watch out for him while I hunt down Mary's killer. And I will do whatever it takes to ensure that Sam never finds out what really happened.

I let the papers fall to the ground as I tried to decide what to believe. Forgery was part of a hunter's tricks of the trade, but somehow I didn't think these pages were faked. The handwriting was an exact match to the rest of Dad's journal, and the condition of the paper and ink supported the entries being written over two decades ago. And I suspected that the ripped edges of these pages would match up perfectly to the torn stubs in the beginning of the journal.

But if this was in fact true, then everything I had based my life around had been a lie.