The episode begins where "Gideon Rises" left off with Stan working on the universe portal. He reveals that he has been studying the secrets of Gravity Falls for at least 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 powers on the machine, and it causes a power surge around town (that Wendy and Gideon notice) that is picked up by a government satellite dish.
The following morning, Stan awakens in his lab to his alarm ringing and remembers the Mystery Shack's grand re-opening that day. In the gift shop, he and the twins excitedly recall the events 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, 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 actually made copies of the pages). Though skeptical that his uncle would give up the book that quickly, he soon 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 clear out the gift shop. When Agents Powers and Trigger arrive on the scene, Stan tries to steer them away and even bribe them. Dipper excitedly greets the operatives and suggests they work together, and Powers gives him his card. Stan discredits his nephew and tells the agents the boy has an overactive imagination, and the officers leave, with Stan bobble-heads as "evidence." Stan proceeds to confiscate Powers' card and tells Dipper to do "normal kid stuff." Dipper expresses disappointment, and Mabel tries to cheer him up by reminding him of the party that night.
As the gang is setting 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 is a bad singer, but Mabel reassures him that one does not need to have a good voice. While Dipper and Wendy play with a black light, Dipper confides his contempt for Stan’s actions, and Wendy agrees to help him retrieve Powers' contact information from Stan’s room. They sneak off as guests begin to arrive. Wendy keeps lookout as Dipper rummages through Stan's belongings—some of which disturb him—finds the card, and calls Powers, though his angry uncle soon enters, as Wendy got distracted by a text. Stan sends Dipper and Wendy away, and he retreats to his lab. While Mabel mingles, Dipper shows to the government agents his journal, but the two quickly dismiss Dipper's claims after seeing some entries in the journal on the "Stomach-faced duck" and the "lepricorn", which they find preposterous. Just as they are about to leave, Dipper proves his point by reading a spell that he randomly picked from the journal, though the spell is revealed to be one that raises the dead and subsequently summons a zombie hoard. As the creatures advance, they scare off the party-goers, and Mabel scolds her brother for doing the one thing she told him not to. Soos attempts to protect them, though he gets bitten almost immediately and transforms into a zombie himself.
As Dipper, Mabel and Waddles flee, Stan is in his lab contemplating Dipper's stubbornness, realizing that he was similarly stubborn at Dipper's age, but he resumes his work, citing that he has too much to do to worry about the kids. However, he quickly changes his mind and arrives to save them just as they are about to be defeated. He sends the kids to the attic as he fights the advancing monsters and reveals that he has always known about the paranormal activity in Gravity Falls, and that he was denying it to keep Dipper and Mabel out of danger.
Just as Dipper is about to give up hope, stating that Journal #3 did not contain any answers for their problem like it normally does, Mabel notes that new text is visible under black light. Dipper discovers 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. From the roof, Mabel introduces the three as "Love Patrol Alpha," and Dipper and Stan less than happily begin singing "Taking over Midnight" with her. The song works, destroying the zombies and the Pines cheer.
Back inside, 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 look for trouble, and in return assures his nephew that he has no more big secrets. Both agree but cross their fingers behind their backs as they do so, implying that neither is really agreeing to anything. Stan remarks that they have a lot of cleaning up to do and inquires where Soos is, only for Soos to walk into the room, still a zombie. Stan tries to attack him, but Dipper finds 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.
Rising from a ditch, and having somehow survived the zombies, Agents Powers and Trigger discuss their awe and question to whom they should report, and they agree that Gravity Falls is indeed the town they're looking for and that they'll need to call in the "big guns". When they see Toby with a blindfold on, they briefly mistake him for a zombie, but quickly see that he is just a "very ugly man."
- Written by:
- Directed by:
- Storyboards by:
- Neil Graf
- Steve Henevelo
- Alonso Ramirez Ramos
- Luke Weber
- With the Voice Talents of:
- Additional Voices:
- Jennifer Coolidge - Lazy Susan
- Jessica DiCicco - Tambry
- John DiMaggio - Manly Dan
- Carl Faruolo - Grenda
- Keith Ferguson - Deputy Durland
- Will Forte - Tyler
- Alex Hirsch - Gnome
- Kevin Michael Richardson - Sheriff Blubs
- Michael Rianda - Thompson
- Gregg Turkington - Toby Determined
- Kari Wahlgren - Shandra Jimenez
- Niki Yang - Candy Chiu
- Stan has known about the secrets of Gravity Falls for at least thirty years. He had been hiding his knowledge to keep the twins safe.
- Tambry knows Tyler.
- 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."
- The fishing hat Stan stitched Mabel's name onto from "The Legend of the Gobblewonker" hangs over one of her bedposts.
- The photo 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."
- One of the pages we see that he has copied has a secret society's symbol on it, which appeared in the short "Stan's Tattoo."
- Several references to previous episodes appear on Dipper's "Big Mysteries" board.
- A picture of Quentin Trembley from "Irrational Treasure."
- 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 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 character 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."
- The author'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 it's 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, was replaced by "Key Vigenére."
- At one point, Stan puts on a six-fingered glove. This might be a clue to the six-fingered hand on the cover of all the journals.
- The Latin incantation Dipper recites to raise the dead translates to "Body, rise. Lord Devil (or Devil Dominion). Conquer the world."
- The use of Zombies as antagonists in this episode is perhaps a reference to the first episode of the series "Tourist Trapped," in which Dipper thought that Norman was a zombie.
- The Binary Code shown coming out of the modified tape machine translates to: STÔNEST“4
- On Dipper's board of "Big Mysteries" the ripped up half of a dollar bill has 618 written under the eye of providence.
- The reason "&ndra" is pronounced "ampersandra" is because the "&" symbol is called an ampersand.
- Among Stan's "Contraband" items are:
- A shark toy
- A slingshot
- Playing cards
- A Tamagotchi virtual pet
- Second time Mabel doesn't wear socks with a sweater ("The Time Traveler's Pig")
- First time Mabel Pines, Dipper Pines, and Grunkle Stan sing together.
- 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, 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 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?"