The episode begins where "Gideon Rises" left off with Stan working on the universe portal. He reveals that he has been working on the portal for 30 years and that he is about to finally accomplish his greatest achievement. He then looks solemnly at a photograph of Dipper and Mabel on his desk, worrying they will be endangered if anyone ever finds out about his secret project, though he quickly dismisses the suspicion. He turns up the power on the machine, which causes a power surge around town (that Wendy and Gideon notice). The surge is picked up by a government satellite dish: once the location is identified, government agents are dispatched to Gravity Falls.
The following morning, Stan is awakened by his alarm clock, having fallen asleep in the lab, and remembers the Mystery Shack's grand re-opening that day. In the gift shop, he and the twins excitedly recall the circumstances of Gideon's defeat. Toby Determined comes and asks them for a picture, though Stan declines because his "camera" is a cinder block. Shandra Jimenez then arrives with a real camera, and the Pines strike a goofy pose. Stan then announces an after-party, and Mabel adds that the family will be performing karaoke together under the name Love Patrol Alpha, without Stan’s and Dipper's consent. Wendy arrives to sell tickets to the tourists, with a successful response.
Stan expresses glee that things are finally going his way, with the townspeople loving him and "the Gideon smell" out of the carpet. Dipper asks for his journal back, and Stan lies that it was "too boring" to finish (though he is shown to have made copies of the pages). Though skeptical that his uncle would give up the book that quickly, he drops it and whisks Mabel off to their room. There, Dipper tells her that he is worried about not being able to crack the mysteries of the town before summer's end, and Mabel assures him that there is nothing left to uncover, but if there is, "Lord Mystery Ham" will find it.
Downstairs, Soos spots a government vehicle, prompting Stan to close the gift shop and have every tourist leave. When Agents Powers and Trigger arrive on the scene, Stan tries to steer them away and even bribe them. Dipper however excitedly greets the operatives, telling them about the journal and suggesting they work together, Powers gives him his card. Stan discredits his nephew and tells the agents the boy has an overactive imagination, prompting the officers to leave, taking Stan bobble-heads with them as "evidence." Stan proceeds to confiscate Powers' card and tells Dipper to do "normal kid stuff." Dipper is disappointed at losing his one chance at getting help with the mysteries of the town, and Mabel tries to cheer him up by reminding him of the party that night.
As the Pines family, Soos and Wendy set up the party, Mabel is overjoyed that the confetti cannon is working and that the karaoke machine has some of her favorite songs. Stan tries to get out of the planned family number by saying his voice is terrible, but Mabel reassures him that one does not need to have a good voice. While Dipper and Wendy play with a black light poster, Dipper vents about losing his opportunity to Wendy, who tells him the card is likely in Stan's room. She encourages him to try and retrieve it, with her help. They sneak off as guests begin to arrive.
Wendy keeps a lookout as Dipper rummages through Stan's belongings — some of which disturb him greatly — finds the card, and calls Powers, setting up a meeting with him. Unfortunately, Stan appears before Dipper can hang up, as Wendy got distracted by a text. Stan sends Dipper and Wendy away and retreats into the lab. While Mabel mingles, Dipper goes off to rendezvous with the agents, finally showing them the journal. Unfortunately, the agents happen upon entries like the "Stomach-faced duck" and the "Lepricorn," which they find preposterous, leading them to dismiss Dipper as a kid with an overactive imagination. Just as they are about to leave, a desperate Dipper finds and recites an incantation, which promptly causes a zombie to emerge from the ground. While its appearance finally convinces the agents, Dipper's success quickly takes a turn for the worse as more and more zombies appear, overpowering the agents and advancing towards the party. While most of the party-goers are gone before the horde reaches the Shack, mistaking the spell's backlash for an earthquake, Mabel, Dipper, and Soos remain and are quickly surrounded. Soos attempts to protect them but gets bitten almost immediately, becoming zombie-like himself and joining the rest of the zombies in running after the kids.
In the meantime, Stan is down in the lab, hard at work. He pauses to contemplate Dipper's stubbornness with some fondness but ultimately decides to put the thoughts out of his head, saying that he has too much to do to worry about the kids. Back upstairs, Dipper, Mabel and Waddles attempt to barricade themselves inside the Shack. They only manage to block the door when the zombies break in, led by zombie-Soos, who's also showed them how to get into the fuse box. Dipper fails to find anything in the journal about defeating the zombies, finally being caught by one. As the zombie raises Dipper towards his mouth, the monster is pushed down, its head promptly crushed: it is Stan, who somehow caught wind of the situation and appears to defend the twins with a bat. He sends the kids to the attic as he fights the advancing monsters with a bat and then brass knuckles, finally heading up himself to bar the door. There, he reveals that he has always known about the paranormal activity in Gravity Falls, and was denying it to keep Dipper and Mabel out of danger.
As Dipper riffles through Journal 3, horrified that it doesn't have a solution for their current situation, he happens to stand over a black light; Mabel notices that new text becomes visible, and it is discovered that the author began writing over the entries with invisible ink. The invisible text reveals that zombies can be defeated by shattering their skulls with a three-part harmony, and Mabel points out that a karaoke number is the perfect solution. The three climb onto the roof, where Mabel introduces the three as "Love Patrol Alpha", with the noise luring all the zombies (except Soos, who remained in the living room entranced by a TV show) out into the yard. She, along with a less-than-happy Dipper and Stan, begin singing "Taking Over Midnight" together. They become excited when the three-part harmony makes more and more zombie heads explode, and as the sun rises, and Mabel hits the last zombie with the confetti cannon, the Pines family stands triumphant over a field of zombie parts.
Back inside the trashed Mystery Shack, Dipper apologizes for the trouble he caused, but Mabel says he has nothing to worry about, as she greatly enjoyed the number they performed. Stan agrees to let Dipper keep the journal for self-defense purposes, so long as he does not go looking for trouble, and in return promises his nephew that he has no more "bombshell secrets"; both he and Dipper cross their fingers behind their backs, however. Stan remarks that they have a lot of cleaning up to do and inquires about his handyman, just as a still zombified Soos ambles into the den chanting "brains!" Stan tries to attack him, but Dipper stops him, having found a cure involving "a lot of formaldehyde and cinnamon." The twins push Soos into the kitchen with a chair, and Dipper expresses excitement at the idea of exploring more secrets with his new-found knowledge of the secret text in the journal.
Meanwhile, somewhere in the woods of Gravity Falls, the battered Agents Powers and Trigger climb out of a ditch. They discuss their awe at what they've experienced and wonder whom they should report to, agreeing that Gravity Falls is indeed the town they're looking for and that they'll need to call in the "big guns." They suddenly bring out their guns upon seeing what appears to be another zombie, but quickly realize it is a "very ugly man": it is Toby Determined, still blindfolded and swinging a bat after failing to hit the piñata at the party in the Mystery Shack.
- Written by:
- Directed by:
- Storyboards by:
- With the Voice Talents of:
- Additional Voices:
- Jennifer Coolidge as Lazy Susan
- Jessica DiCicco as Tambry
- John DiMaggio as Manly Dan
- Carl Faruolo as Grenda
- Keith Ferguson as Deputy Durland
- Will Forte as Tyler Cutebiker
- Alex Hirsch as Gnome
- Kevin Michael Richardson as Sheriff Blubs
- Michael Rianda as Thompson and Lee
- Gregg Turkington as Toby Determined
- Kari Wahlgren as Shandra Jimenez
- Niki Yang as Candy Chiu
- Casting by:
- Stan has known about the secrets of Gravity Falls for at least thirty years. He had been hiding and lying about his knowledge to keep the twins safe.
- Tyler Cutebiker receives Tambry's social media posts.
- The episode resumes immediately following the final scene of "Gideon Rises," in which Stan activates the Universe portal using the journals.
- There are several items in the twins' bedroom that they acquired from previous episodes.
- Mabel's '#2 Boss' mug from "Boss Mabel."
- Mabel's fishing hat that Stan made for her from "The Legend of the Gobblewonker" hangs over one of her bedposts.
- The photo of Candy and Grenda that was ripped up during the song number, "Mabel Girl" in "Boyz Crazy" has been taped back together and hung on Mabel's wall.
- The grappling hook Mabel received in "Tourist Trapped" is seen in her hand.
- The Pterodactyl tooth Dipper got in "Land Before Swine" now hangs beside his binoculars.
- The paper hat map Mabel folded up in "Irrational Treasure" sits on a table.
- Stan uses the Cloning copy machine in his office first seen in "Double Dipper."
- Several references to previous episodes appear on Dipper's "Big Mysteries" board.
- "Experiment 78," the tag found on the Electron Carpet from "Carpet Diem."
- Gideon's Mystic Amulet from "The Hand That Rocks the Mabel."
- A picture of Quentin Trembley from "Irrational Treasure."
- A photo of the Summerween Trickster from "Summerween."
- The newspaper article of Gideon's arrest in the Gravity Falls Gossiper.
- Dipper mentions Bill's prophecy that everything will change from "Dreamscaperers."
- A number of pages in Journal 3 are shown again, including:
- The blue UFO key chain Stan offers to Agent Powers and Agent Trigger is the one Mabel uses in the beginning of the short "The Hide-Behind."
- Tyler Cutebiker is seen wearing a combination of the puma and panther shirts from "Dipper vs. Manliness," in which he couldn't decide between the two.
- Several characters from previous episodes show up to the dance party:
- In Stan's room, there are a few items from previous episodes:
- Dipper uses the shovel Soos gave him in "Tourist Trapped" to fight zombies for just such a situation.
- The symbol of the Blind Eye Society appears, foreshadowing their appearance in "Society of the Blind Eye."
- Ford's underground bunker is revealed in the journal, which Dipper and company explore in the following episode, "Into the Bunker."
- Viewership: This episode was viewed by 2.4 million viewers on its premiere night.
- There is a new backwards message at the end of the theme song. It says "Key Vigenère," which is the new credits cipher.
- In the credits, the name of Agent Powers' voice actor, Nick Offerman, is replaced with "Key Vigenére."
- At one point, Stan puts on a six-fingered glove, which must have belonged to Ford Pines.
- The Latin incantation Dipper recites to raise the dead translates to "Body, rise. Lord Devil (or Devil Dominion). Conquer the world."
- The reason "&ndra" is pronounced "ampersandra" is because the "&" symbol is called an ampersand.
- Among the items in Stan's "Contraband" box are:
- A shark toy
- A slingshot
- Playing cards
- A Tamagotchi virtual pet
- During the ending credits of this episode, there is a cryptogram that reads "SMOFZQA JDFV." Once decoded using vigenère cipher, it reads "WELCOME BACK."
- Found on Gideon's prison cell wall is the keyword: "WIDDLE"
- On the satellite footage of Gravity Falls that the agents are looking at, there are numbers at the bottom that say "5192362116 1896 41619..." When separated correctly it can be said, "5-19-23-6-21-16 18-9-6 4-16-19..." Using the combined cipher it translates to "SEARCH FOR THE..."
- On the bottom of Dipper's "Big Mysteries" board, written on the board frame itself, there is a cryptogram that says "TEV FP TBKAV PL MBOCBZQ," which decodes into "WHY IS WENDY SO PERFECT."
- On Agent Powers' card, there's a number that says, "6-12-1-7," using the A1Z26 cipher it translates to "FLAG."
- At the Leprecorn's section, there are two cryptograms. The first is "ZDWFK RXW," which says "WATCH OUT," The second is "NLOO PH SOHDVH," which translates to "KILL ME PLEASE." Both are in the Caesar cipher.
- The page section revealed at the end of the episode says, "4-16-19 11-23-10 20-9-1-10-5-4-23-15-6-5 15-5 2-19-6-25 21-12-19-2-19-6" on the left and on the right says, "21-23-10 16-19 16-15-20-19 16-15-5 8-12-23-10-5 18-9-6-19-2-19-6?" After being put through all of the ciphers, it translates to "THE MAN DOWNSTAIRS IS VERY CLEVER" and "CAN HE HIDE HIS PLANS FOREVER?"
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