AN: This ties into my other Mystery Spot oneshot, Thursday. It can be read alone, but it might make more sense if you read Thursday first. I hope you like it!

There are some things Dean just knows. He knows the words to every Metallica song ever written. He knows his way around every single weapon in his trunk. He knows what goes bump in the night. And he knows that Sam is lying.

He doesn't comment on it at first. He pretends to believe the "it was a bad dream" story. Heck, he even lets it slide the first hundred times Sam says he's okay.

It's starting to freak him out a little bit. Scratch that, it's starting to terrify him.

Dean pretty much raised Sammy; he knows Sam better than anyone else in the world. Or at least, he knows Sammy. But this person sitting in the passenger seat isn't Sammy. Not completely.

This Sam is cold, quiet, kinda OCD, and hasn't smiled—really smiled—even once. This Sam is different. The kind of different that can only be achieved over months and maybe even years. It's been five days.

And it's not just Sam's new habits that are freaking Dean out. No, then there's the hunts. As they were driving away that Wednesday, Dean asked Sam if he had a preference as to which direction they headed, and Sam immediately reeled off the exact location of their next job. When they got there, Sam knew all the details without doing research. He knew where to go, who to talk to, what they were dealing with and how to kill it.

And when they were done, Sam had just looked at him and given another location.

And as if that's not enough, there's the hovering. Sam won't let him out of his sight, and sometimes not even out of arm's reach. He's even caught Sam watching him at night. It's getting to be more annoying than anything, although concerning is way up there on the list.

Wednesday was especially awful. Sam wouldn't stop staring at Dean. He followed him everywhere, tense and quiet, carrying more weapons than usual. Dean tried to let it go, but overnight Sammy had turned into a menacing bodyguard and that was not okay.

But Thursday morning, that was when Dean got really scared. He woke up before Sam and went to the bathroom to get ready. When he came back, his heart nearly stopped. Sam was on the floor, curled up against the bed, shaking like a leaf. He was muttering something, but all Dean could catch was "no more Thursdays."

What beef could Sam possibly have with Thursdays? Sure, Tuesdays were pretty much shot to hell, and nobody really likes Mondays, but what had Thursday ever done to him? But those were all the thoughts Dean had time for, because then he caught sight of what Sam was clutching desperately in his hands.

A gun.

Dean was across the room in an instant, moving on auto-pilot. His brain was shutting down, and all he could think was "stop Sammy."

"Sam!" Sam didn't even seem to hear him. Dean dropped to his knees next to his baby brother, shaking his shoulder. "Sammy!"

Finally Sam looked up. The look of relief that crossed his face almost knocked the breath out of Dean. "Sammy, why don't you drop the gun and we can talk about this."

"Dean!" Even the bear hug of Wednesday couldn't compare to the bone-crushing embrace Sam now subjected Dean too.

After that whole fiasco, Dean decides to just suck it up and let Sam hover.

But there are a lot of things Dean doesn't understand. Yeah, Sam's always been a bit of a neat freak, but suddenly he flinches every time he sees the jumble of weapons in the trunk and he smoothes out every insignificant wrinkle in his sheets. Dean just doesn't get it.

Dean also doesn't get why this stranger claiming to be Sam seems so much like Sammy sometimes. Not the Sammy Dean's been hunting with for the past few years, but the five-year-old, scared as hell, sees Dean as a magic teddy bear Sammy. There are glimpses of it every so often. Dean will see it in Sam's eyes; he'll hear it in his voice. And it scares him.

The whole situation is scaring him to death—he wonders if he ever died that way on Tuesday—but he doesn't know how to fix it.

Dean glances over at the dark shape in the passenger seat. He can see Sam's head resting against the window and hear his slow, even breaths, but he knows that Sam isn't asleep. He wishes everything could just go back to how it was when they were kids. Back to when life was simple. When he knew everything about his baby brother. When they had no secrets from each other. When Sam trusted Dean implicitly and was comforted by his mere presence. Before their lives really went to Hell. Before the Tuesdays. Before Sam became so broken he was barely recognizable.

Dean sighs quietly, staring hopelessly out at the dark road ahead.

There are some things Dean just knows. But how to fix Sam isn't one of them.