A/N Not my best work, but the idea wouldn't leave me alone. It's kinda rushed since I wrote it in an hour, and hasn't been proofread either so it's also probably crap. But seriously, the idea would not leave me alone at all! Had to get it written down and out of my system. I don't think this will be a very long story but I'm not sure yet.

Anyway, hope you enjoy!

Imposter

"Are you crazy were all gonna—"

He never got to finish his sentence because at that moment the clock reached zero and there was a powerful burst of energy. The last image he saw before everything went white was his sister hovering in the epicenter of the portal's blast.

Dipper knew the moment Mabel made her decision, probably before she did. She was always so trusting and willing to see the good in everyone, wanting to give them the benefit of the doubt. So he fought trying so hard to make her see that trusting Stan was a bad idea, that if there was ever a time when she should think with her head instead of her heart, it was then. But as he expected deep down, she let the clock reach zero and for a moment Dipper was certain they were all dead.

But then his head started throbbing and he cautiously blinked his eyes open and saw that somehow, he had miraculously survived. He saw Soos and Stan picking themselves up from the floor but no Mabel.

Where did she go?

He couldn't see her anywhere and he remembered that while he, Stan and Soos were pushed away from the machine, the portal kept trying to pull her towards it. Panic started to build within him as he looked to the portal and saw not his sister, but a man, walking towards them as the last remnants of the machine's power dispersed into the air and died down.

The man picked up journal #1 with a six-fingered hand and he rubbed his head, in shock, "What? Who's that?"

"The author of the journals," Stan explained as Dipper's attention wavered between looking for Mabel and studying the man he had been looking for all summer. "My brother."

The man lowered the hood concealing his face, revealing a man nearly identical to Stan and Dipper's jaw dropped in shock.

"Is this the part where someone faints?" Mabel asked, and Dipper startled because she appeared out of nowhere.

Where did she come from?

"I'm on it!" Soos volunteered as he fell to the ground.

Seriously, she came literally out of nowhere.

0-0-0

The next few days were chaotic, and they were so busy picking up the pieces that he Dipper didn't really have a chance to notice anything different about Mabel. She was a little off, but so was everyone else. After all, it was an insane couple of days between Stan's arrest, discovering the Portal, Mabel letting it open and then the Author of the journals appearing, it was too much to take in but in the back of his mind Dipper wondered how Mabel could've appeared suddenly beside him, seemingly fine when she had seemed to have vanished at first and everyone else had been pretty banged up.

She seemed completely unaffected by the explosion that came with the clock reaching zero. Days later Dipper could remember with clarity the painful heat of the blast, so intense he still can't believe they survived with only a few bruises but Mabel…she had been right there in the literal center of it. While he wasn't complaining, because it's not like he wanted harm to come to his sister, it was still weird that she escaped without a scratch.

It wasn't until three days after the Author appeared that Dipper began to really suspect that maybe the girl who claimed to be Mabel, wasn't really her. It was a crazy thought, he realized that, one that terrified him but once the idea crept into his mind, he couldn't shake it.

It was the little things here and there that made him wonder.

One morning during breakfast she reached for the milk, which in of itself isn't all that strange except for the fact it's Mabel, who hates plain white milk. Sitting in the fridge meanwhile was a fresh batch of Mabel Juice. When he asked about it she made a face. "Too much sugar," she replied, "it's kinda gross."

Neither Grunkle Stan nor Grandpa Stanley seemed to bat an eye, but Dipper knew better. Dipper knew that was a big clue that something was wrong because to Mabel, there's no such thing as too much sugar. Not unless she was sick, but she seemed perfectly fine.

The next day Mabel decided that Grandpa Stanley needed a new sweater so she grabbed some navy blue yarn and got to work. It's a very Mabel thing to do, she's made one for Grunkle Stan, Soos and Wendy, and he's got a few of his own that he never wears. She makes everyone she cares about a sweater, usually for Christmas or birthdays, but sometimes she doesn't need a reason other than, just because. She's also super fast at knitting, so when he found her in the living room grumbling about the stitching, it made him take pause. She had been at it all afternoon but when he spotted her later on she had barely made any progress and was starting to unravel what little progress she did make.

"What's wrong?"

"I messed up," she griped, "have to start over."

The thing about Mabel, she rarely makes mistakes while knitting, and the odd time she does she never seems to have a problem fixing it.

"Are you OK?" he asked finally.

"Yeah, why?"

"You seem kinda…off. You don't seem to be yourself lately."

"Well, we've been through a lot the last couple of days," she shrugged and he had decided maybe she had a point.

It's what happened the following day that made Dipper really start to consider the possibility that maybe he's onto something.

It was the grand re-opening of the Mystery Shack. The Portal had done some damage but after a week everything was in order and ready for business. So Dipper, Mabel and Wendy ran the gift shop, while Stan and Soos ran a tour and Stanley slept. He slept a lot since coming back. Stan was worried, said something about PTSD and made an effort not to push him about what went down thirty years ago and all the time since. It's what kept Dipper from trying to pick at his brain, because he was the Author of the journals after all, there were so many questions. But he gave him his space, and Stanley seemed to appreciate it. Stan was also taking house arrest in stride and everything was otherwise pretty much back to normal.

But then a couple of tourists and their son walked in. Dipper groaned the moment he saw the kid. He looked to be about their age, and he definitely seemed to be Mabel's type. Of course just being a cute boy the right age was all Mabel needed to instantly have a crush.

Not this time apparently. There was no awkwardly forward attempts at flirting, at least not from her. He did all the flirting. It was painfully obvious and a little embarrassing when he went on about how pretty she was. Mabel was polite, but she didn't even seem to notice.

"Dude!" Wendy exclaimed after he left, "What was that?"

"Huh?"

"That guy was super cute and totally flirting with you!"

"He was?" Mabel seemed genuinely surprised, "Oh. I didn't notice."

"OK, who are you and what did you do to Mabel?" Wendy joked.

Even though it was said in jest and everyone laughed, Dipper couldn't help but wonder the same thing. Only he was completely serious.

Who are you? And what did you do to my sister?

Maybe he was just being paranoid, and he really hoped he was. But no matter how he looked at it, Mabel wasn't acting like herself. Sure, it was a whole lot of little things, but those little things seemed to be adding up to something being very wrong. And maybe there was nothing to be concerned about, after all, it seemed to make sense that she'd be a little out of sorts after all that had happened, but there was something else, something he couldn't quite put his finger on that made him wonder. That made that crazy little thought that lingered in the back of his mind to take hold. Something to do with the Portal. Either way, he had to be sure.

A/N Thanks for reading! Please let me know what you think!