When the series started, Dipper and Mabel were shipped off for the summer to work at their Grunkle Stan’s Mystery Shack with his two regular employees. Maybe we should get to know one of them a bit better.
No, not Soos. The other one. Wendy.
What does Wendy do at the Mystery Shack? As little as possible. She’s a teenage girl who’d rather slack off than do actual work. You know, like I do when I type these things. Any excuse to watch cartoons and all…
But, it turns out Dipper has a thing for her, and he’d really like to impress her. She’s going out with her friends, and all Mabel can do is embarrass Dipper by sharing stories of some sort of lamb dance he used to do for their mother. He had a costume and everything.
But if Wendy and her friends are going out, what can Dipper do if he and Mabel are too young to go along? Well, he can lie about his age. If he’s 13, he’s barely a teenager and he can go. Granted, that also means Mabel can go, but it works and the twins get to go hang out with some older kids.
What is their destination? An allegedly haunted abandoned convenience store, possibly due to a bad murder. Though he’s hesitant going over the fence, one of Wendy’s friends is particularly jerktastic, so Dipper actually climbs down a vent on the roof to let everyone in, and apparently the electricity still works and the food’s edible. Mabel finds some kind of colored sugar treat that was actually illegal to sell in the United States and started gobbling it like crazy, and that just made her go crazy with the resulting sugar high.
And then Dipper spots a disembodied brain with a pair of eyeballs floating in the freezer. Yeah, this is Gravity Falls, so the place really is haunted. And before Dipper can get the others out without looking like a wuss, Wendy’s friends start disappearing. The girl who couldn’t stop texting was trapped in the surveillance video. The guy playing the video game was trapped inside. Mabel might actually be possessed. And so it goes until only Dipper and Wendy are left. Could Stan help? Well, not if he’s so absorbed in an old romantic movie that he was forced to watch when no one could give him the remote that he can’t answer the phone.
However, Dipper consulted his book and knows the ghosts need to be appeased. And he also notes the reasons people disappear is they happen to be behaving like obnoxious teenagers. Dipper then manages to get the ghosts to appear in a friendlier manner by confessing he’s only 12.
Yeah, the ghosts are Ma and Pa Duskerton, the elderly couple that ran the store. They hated teenagers and banned them from the store. Then the teens came back and played rap music outside and caused the Duskertons to die of simultaneous heart attacks. Yes, there was no murder, just bad tickers. And Dipper can save everyone if he’ll just do the embarrassing lamb dance again. He does, and everyone is released. Wendy was the only witness, but she indicates she won’t tell.
Now it’s just time to go back to the Shack, where Stan tosses the TV out a window and Mabel is nursing a sugar hangover. You know how it is.