Say what you will about Mabel Pines, she may have an archrival in the form of Pacifica Northwest, but she doesn’t really hold a grudge or anything along those lines. You’ll never see a soul more oblivious to having an archrival than Mabel.
Stan and the twins are stuck in traffic in the middle of town when Stan realizes the worst: the traffic isn’t moving because they’re surrounded by covered wagons, not slow-moving cars. It’s Gravity Falls’ annual Pioneer Day, the day the town celebrates its founding by an ancestor of Pacifica Northwest and how in older times you could legally marry a woodpecker. And yes, Pacifica is snotty about the whole thing, going so far as to mock Mabel for being silly when Mabel gets up to talk.
All that talk of being silly gets to Mabel. So, when Dipper discovers in his book that an old legend says the Northwest family did not found the town, the twins team up to find out the truth. Dipper loves to solve mysteries. Mabel wants to be taken seriously.
One problem: the town’s two dumb cops, Sheriff Blubs and Deputy Durland, are being told by agencies unknown to stop them.
But here’s the thing: Mabel actually figures out all the clues. The parchment in Dipper’s book makes no sense until she folds it into a hat and it reveals a map. A museum exhibit makes no sense until she flops over and looks at it upside down. And she opts to use a pointing statue to pick her own nose, revealing a secret passageway that tells the true story of the founding of Gravity Falls.
Who really founded Gravity Falls? Sir Lord Quentin Trembley III Esquire. He was the eighth and half President of the United States.
See, he was an embarrassment, so when he rode a horse backwards out of Washington and disappeared in what became known as Gravity Falls, the government pretended William Henry Harrison was president and the Northwest ancestor founded Gravity Falls. It turns out that ancient Northwest was actually the village idiot. President Trembley won the election by a literal landslide when said landslide landed on top of all the other candidates. He declared war on pancakes, put six babies on the Supreme Court, and wrote the E-pants-imation Proclamation outlawing pants. He was just plain silly. Only a person as silly as Mabel could have deciphered the clues, as Trembley had sealed himself inside peanut brittle to make himself immortal before he disappeared.
How do Dipper and Mable find all this out? Well, Blubs and Durland catch up and run a filmstrip. Trembley is sitting nearby. Now the two law enforcement officers are taking the brittled-up Trembley and the twins in a crate back to Washington.
Could Stan help? Not really. His grumpy irritation over his mechanic pretending not to know what a car was on Pioneer Day got him locked in the stocks, where Lil Gideon and Pacifica can pelt him with tomatoes.
So, once again, the twins need to rescue themselves. Mabel accomplishes that herself when she takes a bite out of Trembley’s peanut brittle cube, it breaks, and Trembley wakes up, ready to continue all things silly. He has the president’s key, which allows him to open any lock in America! Too bad there are no locks on the inside of that crate. But then a woodpecker that sounds like Trembley’s third wife shows up and manages to drill the box apart. And since Trembley never resigned from the presidency, he can order a grateful Blubs and Durland to forget their orders, never mention it again, and take their dream vacation. Trembley then makes Mabel a Congressman, gives Dipper the President’s Key, and rides off on a horse backwards.
So, after Dipper unlock Stan from the stocks, Mabel has the opportunity to not be silly and ruin Pacifica’s whole belief system by showing her the top secret documents proving her great-great-great granddad was the village idiot and not the town founder. Does she? Nah. She’s fine with being silly. She doesn’t like hurting people.
Dipper, on the other hand…