When Gravity Falls' holiday Pioneer Day comes around, Grunkle Stan, Dipper, and Mabel drive through town, looking at many various out-dated activities and ceremonies. Grunkle Stan utterly hates Pioneer Day and tries to escape, but in vain. Later, Sheriff Blubs calls the town to the Pioneer Day commencing ceremony, where Pacifica Northwest makes an announcement about her great-great grandfather, Nathaniel Northwest. Pacifica asks for volunteers to say something about themselves, and of course, Mabel comes up, but Pacifica makes Mabel feel bad by telling her she's way too silly to participate, and Mabel decides she has to be more serious and never be silly, and proceeds by taking off her nacho earrings and her sweater and putting her "serious" face on.
Meanwhile, Stan gets thrown into stocks after threatening the mechanic. He is then pelted with tomatoes by Gideon after mocking his outfit.
Dipper then remembers an article in his journal that says Nathaniel Northwest may have been a town fraud. Mabel decides that solving a mystery will prove that she can be serious. Enclosed in the journal is a map with the triangle symbol. Behind the statue of Nathaniel Northwest, Sheriff Blubs and Deputy Durland are eavesdropping on Dipper and Mabel. They immediately inform a dispatcher of Dipper and Mabel's seemingly suspicious scheme.
Dipper and Mabel head to the library to look up the symbols on the map. Dipper finds a symbol that means fire and is the same shape as the picture on the documents. Dipper thinks they should burn the document until Mabel makes a hat out of the paper, and she thinks this was silly, but it actually shows them a map to the Gravity Falls Museum of History.
Dipper dramatically says they're going to have to break in. Dipper and Mabel head to the museum where a lady says "Here are your free Pioneer Day passes and balloons, blue and pink!" Dipper then dramatically says as the camera zooms in on his face, "We're in." There's an abstract painting shaped in a triangle, and when Mabel turns upside down, it reveals a pointing angel, and she comments that she saw that statue in the Gravity Falls Cemetery, which they hurry to.
Meanwhile, Stan still struggles to get out of the stocks. Pacifica then offers to get him out if he says that the Northwests are the best family in Gravity Falls. Stan then writes her a note with his mouth that says "YOU STINK!" Pacifica then gestures the other townsfolk to throw more tomatoes at him.
Once at the cemetery, Mabel sees the statue, and she pretends that the statue is picking her nose. She bends the statue's finger, opening a secret passageway. Mabel and Dipper enter it, and Dipper says to watch for booby traps, and Mabel then laughs at his words. They go down the hallway when Mabel steps on a tile, which triggers tranquilizer darts. They dodge the darts and go down a hallway revealing many top secret documents (e.g., Abraham Lincoln's hat was covering up a hand on his head; Ben Franklin secretly was a woman).
They come across a document called the Northwest Cover-up, and it is revealed that the true founder of Gravity Falls was Quentin Trembley. Sheriff Blubs and Deputy Durland reveal that they have been following the twins and had been tasked with finding Trembley, playing a film for Mabel and Dipper showing the truth about Gravity Falls. Sheriff Blubs then says he must ship them off to Washington D.C., revealing that Quentin Trembley had encased himself in a peanut brittle cube in the hopes it would keep him alive.
Sheriff Blubs and Deputy Durland get on train bound for Washington D.C., having placed Dipper and Mabel in a giant crate along with the still encased Trembley. Mabel, in sadness thinking that she caused this, breaks off a chunk of peanut brittle and eats it, freeing Trembley, who miraculously survived as a result of the peanut brittle's "life-sustaining properties" (as stated by Mabel). They escape, but are caught by Blubs and Durland. They climb to the roof, where Trembley recalls that he never signed a resignation, and that he ate a salamander and jumped out the window instead. Trembley then orders the cops to stop and take a vacation, which they gladly agree to.
When Dipper, Mabel, and Trembley head back to town, Trembley decides to make Mabel a congressman and gives her a hat. Dipper receives the President's Key, which can open any lock in the whole America. Back in town, Mabel accepts her silliness and doesn't care if Pacifica knows the truth or not, but Dipper shoves the proof in Pacifica's face, calling her family a "sham" and telling her to "deal with it." He then says that revenge is underrated and that it felt "awesome." After Trembley departs, the twins then use the President's Key to get Stan out of the stocks.
During the end credits, it shows Quentin Trembley and the babies of the Supreme Court. Trembly is trying to discuss things, but it's hard with four babies, and Quentin comments that it is a "dark day for America."
- Story by:
- David Slack
- Written by:
- Directed by:
- Storyboards by:
- With the Voice Talents of:
- Kristen Schaal as Mabel Pines
- Jason Ritter as Dipper Pines
- Alex Hirsch as Stan Pines, Quentin Trembley and Old Man McGucket
- Jackie Buscarino as Pacifica Northwest
- Keith Ferguson as Deputy Durland
- Kevin Michael Richardson as Sheriff Blubs
- Gregg Turkington as Toby Determined
- Thurop Van Orman as Gideon Gleeful
- Additional Voices:
- Casting by:
- Dipper mentions Mabel and Pacifica's rivalry, which was first instigated in "Double Dipper."
- A secret document reveals Ben Franklin was, in fact a woman, foreshadowed by Stan in "The Legend of the Gobblewonker."
- A secret document mentions a time devouring baby trapped in a glacier in Antarctica. He appears in the next episode, "The Time Traveler's Pig."
- The serial number on the negative twelve dollar bill can be deciphered into the word "BLIND," an early hint to the Society of the Blind Eye.
- Dipper ends up accepting Soos' nickname for himself and Mabel, the "Mystery Twins," from "Headhunters."
- Viewership: This episode was watched by 3.869 million viewers on its premiere night.
- During the top-secret film, the seal says "Official United States Government Cover-Up Seal."
- Bill appears on the negative twelve dollar bill, as a reference to the Eye of Providence that appears on the back of the dollar bill.
- In the Disney Channel Asia airing of the episode, the line "Bottom line, George Washington was a jerk." was cut; along with Mabel's subsequent "Agreed."
- Mabel is able to use nachos as earrings thanks to "very sticky nacho cheese."
- In addition to the true identity of Nathaniel Northwest, the Northwest Cover-up document also reveals that:
- Thomas Jefferson was actually just two kids in an overcoat standing on each other's shoulders.
- The current and forever President of the United States is actually Santa Claus. Under the reign of Mr. Claus, America is not a democracy, but a jollyocracy.
- The statues in Mount Rushmore are actually gigantic presidential-faced robots that will be called into action when America needs them most.
- An enormous, evil, time-devouring baby from another dimension is frozen in an Antarctic glacier.
- Writing jokes for cartoons is more important than sleep.
- Reciting the pledge of allegiance backwards will give one secret wizard powers.
- This is one of only two full-length episodes in the series (the other being "Northwest Mansion Mystery"), in which Soos has no lines nor does he appear onscreen.
- During the ending credits of this episode, there is a cryptogram that reads "V. KOFIRYFH GIVNYOVB." Once decoded, it reads "E. PLURIBUS TREMBLEY." In Latin, this means, "Out of many, Trembley," which is a reference to a phrase "E pluribus unum" ("Out of many, one") that appears on the Seal of the United States and was a de facto motto of the US until 1956.
- On the negative twelve dollar bill, the serial number is "Z 0239548604 Z." After grouping the numbers into pairs and then adding up the sums of the digits within those pairs, you get "2 12 9 14 4" which translates into "BLIND," an early clue as to the existence of the Blind Eye Society.
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