PART 1:
Off the coast of southern Georgia, a man and his son are fishing despite the foggy, overcast morning. The son points out an island surrounded by thick, writhing fog to his dad, confused about where they are. The scared father tells the son that it is Gracey Island, the son having always thought the island was just part of a scary story. The son is in denial about the rumors of ghosts and mermaids until something bumps the boat. They look into the water to see large numbers of manatees swimming in the same direction, relieving them until a human head pops out of the water, half-human and half-fish people appearing alongside the manatees.
The father grabs a net, intending to capture one of the merfolk, but a merman with a seashell necklace grabs onto the side of the boat, the son preventing his father from attacking. The merman warns the two to leave the island, a female manatee in a pink dress and crown surfacing and agreeing with the merman. They dive down when a wail sounds from the island, the fog parting long enough to show writhing ethereal shapes before the son quickly drives the boat away. Downriver, the merman and manatee debate having to evacuate their communities from around the island if the haunting continues much longer. The merman says he knows of two people who could help if they were nearby, but the manatee has a solution nearer at hand. She pulls out a cellphone and calls her father, asking him to cash in on the favor owed to him by the Guardsman.
With her friends asleep in the pre-dawn light, Mabel sits on a beach, arguing with herself about leaving Waddles behind and if she can't protect her pig, that she can't protect herself or her friends. Wendy comes over and tries to cheer Mabel up, but Mabel tells Wendy about her fears, most of which have been brought on by Dipper's wanting to use magic to find Waddles the day before. Wendy assures her that all of them will be fine despite her condition and whatever is going on with Soos talking in his sleep.
Dipper climbs out of the car and tells them Zander texted and asked them to call. They wake up Soos and call Zander, who assures them that despite some unsolved mysteries from the fight with Graupner, everyone is either fine or will be soon. Dipper tries to change the subject to Starkissed, but Zander tells them that he's actually calling about them handling a favor the Manatee King called in. Dipper isn't happy about the situation, but when Zander tells them an island was cursed 150 years ago and has been growing stronger since the Stone was destroyed, they all agree to handle the situation.
He tells them to go to Fancy Bluff Creek so the locals who contacted him can transport them to the island. Soos asks for as much info as they can get, but since this came up so last minute, Zander's info is limited to the wikipedia article about the island, and all that says is that it was named after the Gracey family who gained and lost influence after the Civil War. Dipper asks if there could be some Starkissed on the island, Zander saying it could be hit or miss on if magic is involved. Dipper comments that he knows a lot about magic even though he's against it, the Guardsman replying that he's had time to learn from his enemies before hanging up on Wendy about to ask him a question. Dipper says that Zander was hiding stuff again, Wendy agreeing with him but insisting they need his help, although Dipper doubtful about trusting another adult who says he's on their side after what happened with Ford three years ago.
They arrive at the creek, Dipper pulling out anything and everything they could potentially need to deal with the curse or, as he believes, the haunting on the island. They head onto the collapsing dock, an oar-less rowboat at the end of the abandoned bluff. They wonder where the locals are, but a familiar voice calls to them from behind the boat. They run over to see Mermando, the twins reuniting with him as he signals for the manatees and merfolk to surface, introducing them to his wife Manatier, the Manatee Queen.
The four of them get in the boat as the menfolk and manatees escort them towards the island, most of them stopping as the boat enters a wall of fog. Mermando and Manatier explain that the fog wall is where the island's curse influences, most of their people having had to evacuate the area. The island comes into sight, dead and dying trees leading to the shape of a mansion, odd sounds echoing around. The boat is pushed to the shoreline, the remaining merfolk and manatees taking it away as soon as the four climb out. Mermando apologizes for not waiting, but tells them about a Sending spell that, as long as you have some common ground with someone, you can telepathically send them a message.
The four of them start heading towards the apparently run-down Mansion, quickly becoming unnerved by the intact structure combined with the broken doors and windows. They enter the mansion, signs of age evident everywhere in the foyer, three hallways on the bottom floor and two curved stairways leading to the overlook. With the warning that the curse will probably start attacking soon, they start looking around the building, eventually discovering an ancient library.
Mabel complains about having to do research, insisting she and Wendy go look in a different room, practically dragging her upstairs. Mabel admits that she's scared about Dipper being tempted by magic and the bad things he seems to forget it has lead to, but the conversation stops when they see a hatchet embedded in an intact door. They open the door to see a bedroom with wedding gifts scattered around, pictures of the same woman, Constance, and a different man on the top of each. Mabel's eye catches a perfectly intact wedding dress and necklace in the corner, but when the hatchet that was in the door crashes into the floor, the girls decide to head back downstairs.
Back in the library, Dipper is looking through a charter book while Soos chucks several other books to the floor. Dipper says that the book talks about the house master Edward Gracey and how he made a living with ships, but it doesn't say anything about curses or give any clues as to what is going on. Dipper hears footsteps come in from the hallway and, without looking, asks the girls to give him one of the books Soos threw. A pink book with a pink metal heart lock is slid to him, the name CONSTANCE HATCHETAWAY on the cover.
Pleased by the find, he turns to look at the girls, but only then realizes he and Soos are the only ones in the room. He calls Soos over, warning him the curse is getting warmed up as light starts to come closer from the hallway. Luckily, it's just the light from Mabel's phone, the two groups quickly sharing their discoveries. Dipper agrees they should go check out what the girls found, assuring the butler that they will leave and let him clean up the library. Slowly, they all realize they just talked to a butler in an abandoned mansion on a cursed island, and the butler is really insistent on cleaning up before the guests arrive for the ball later.
PART 2:
The four of them watch in shock and horror as the butler moves about the room, anything he touches with his cleaning supplies restoring itself to perfect condition. After confirming that the butler is a ghost, they go outside at his request, Dipper convinced the 'curse' is actually a major haunting. This suspicion is confirmed when they see dozens of ghost butlers and maids walking around the hallways, restoring everything just like how the one in the library did.
Dipper admits that they are not prepared for a haunting of this large a scale, and since helping every ghosts present get what they want is out of the question, they decide to head back to the mainland and stock up on battle supplies. Unfortunately, standing in front of the entrance is the ghost of Edward Gracey, the late house master. He comments about them being very early for the event and their lack of formal clothes, but when they try to say they are leaving to get changed, he insists they not worry about it, something Dipper knows he would never allow back when he was alive.
Dipper comments on his liberalness, but Edward mentions dark times in his family, pointing them to the gorgeous young woman observing them from the overlook before offering to give them a tour of the mansion. He takes them back to the library, mentioning that his daughter and her spouse would one day inherit the mansion before telling the butler to find the missing book from his former wife's collection.
He starts leading them to the ballroom, Wendy mentioning to Dipper that her normal wraith-senses that let her decent supernatural things isn't working quite right, despite the ever increasing number of ghost servants. As they enter the ballroom, Dipper waiting for disaster to strike, he gets a weird feeling. He looks past the three chandeliers in the ceiling to see the woman from before watching Mabel from an overlook. Wendy also noticed the woman, and tells Dipper that, while she knows the woman is dead, she doesn't get the usual warning signal that lets her get a read on something.
The tour continues, Edward warning them to not go in the basement before leading them outside. Soos comments that it looks darker, but when Dipper pulls out his phone to check the time, the clock continues to change to random times displayed in a number of ways. Edward shows them the backyard overlooking the gravestones, Dipper getting the weird feeling yet again. He looks up to see the woman watching them, Mabel in particular, from an upstairs window, and the sense of unease only grows when they go back inside to see the rest of the servants watching them.
As the four of them debate how to leave, Edward leads them back to the foyer, the servants following behind them and the woman again watching from above. Dipper tries to get Edward to let them leave, but Edward insists in them remaining and being his guests for the evening. The woman comes downstairs and asks her father to introduce her, Edward introducing his daughter Constance Hatchetaway. Dipper again tries to leave, but Constance insists they stay for her party, Edward becoming angry at them for wanting to leave.
Then wind picks up outside, blowing the windows open, Edward and Constance excited because the guests have finally arrived. Easily a hundred ghosts of people long dead enter quickly, and more continue to float through the windows. Then the front door is pushed down and the undead join the party as well, an angry Edward telling the scared four that anyone who is invited to Constance's party will show up, and since they have been invited, they are not allowed to leave.
The four of them start running, eventually entering the library to avoid the ghosts and undead chasing them. Soos panics when a statue come to life and hurls it at the opposite doors, throwing books everywhere in the process. Dipper notices something about the books but is only able to grab one before they have to run again, the servants coming after them. They hide in a music room, able to avoid detection and be alone for a moment, except for something trapped in a coffin in the room.
That is put out of their mind when Dipper announces that the book he grabbed is Edward's journal. They look through it to see several similar entries describing how he killed his daughter's husbands and forged notes that left all of the mens' wealth to Constance and, indirectly, him. Realizing that is most likely the cause of the haunting, they are unable to plan how to handle the husbands' ghosts because Constance reveals herself to be behind them, causing them to run yet again.
They run back into the ballroom, intending to head outside, but their exit is blocked by curtains covering the windows around the room, Edward Gracey and what he eventually reveals to be just under 1000 of his fellow ghosts encircling them. Dipper pulls out a water gun filled with anointed water and threatens to start shooting if he doesn't get the answers he wants, the most important of which is what the party is for. But the gun is pulled from his hands and flies to where Constance is watching from above, quickly being disintegrated by her power.
She says that they want to end the curse once and for all, revealing that the cause isn't the husbands her father killed, but the lack of true love they are able to feel because they are ghosts. She says that to break the curse and let everyone move on, someone needs to remind them what true love is, Mabel immediately volunteering her services. She reaches to shake Constance's hand, but as soon as she does, Constance makes her pass out and begins floating away with her.
Dipper tries to get Mabel back, but the ghosts start moving in, Edward commanding they be brought to the dungeon. Wendy notices a chair and makes the boys promise they will run of they get the chance, Dipper agreeing even though he doesn't want to leave Mabel behind. Wendy runs and grabs the chair and hurls it at the curtains, breaking the glass behind them. Dipper and Soos jump outside but Wendy is grabbed by a number of ghosts and is held back, barely having enough time to tell the boys to get help before the glass fixes itself, cutting her off.
Soos insists he and Dipper get reinforcements before charging in how they are and most likely being captured. Dipper, realizing a storm is brewing and that it is already night, agrees, but they aren't able to do much as zombies start climbing out of the ground, forcing them to run again. They both pull out their phones, but Dipper's doesn't have a signal and Soos is forced to use his as a weapon against one of the zombies. Luckily, Mermando is waiting for them by the water's edge, having heard the noise coming from the island. Unfortunately, zombies start coming out of the water as well as from the land, and Dipper tells Mermando to save himself, he and Soos running away through the trees.
They stop in a clearing, Dipper now having the idea to attempt the Sending spell Mermando told him about so he can ask Zander for help. He desperately tries to find common ground between him and Zander to establish a connection, saying out loud that Mabel is in trouble and they are in over their heads. Soos tells him the zombies are hearing him, and Dipper gives up on the spell, he and Soos running through the graveyard and eventually taking cover in the mausoleum, the zombies running past and leaving them alone.
Curtains and empty coffins around them, they start trying to think of a plan, but everything Dipper knows how to do would never work since there are 1000 ghosts present. Dipper then gets the idea to use magic and pulls out all three Journals, looking for something that could level the playing field, though he doesn't know what it would be. Soos mentions that he might know of a way out of the situation, but before he can tell Dipper about who he met, the doors shake and they are forced to hide.
Soos goes in the curtains while Dipper grabs the Journals and jumps in a coffin just before the doors crash open. Dipper can see enough to tell that the person isn't Zander or a zombie, but whoever it is notices Soos in the curtains and tells him to come out. Soos tries to attack but gets tripped up, the person's demand for answers being cut off by Dipper hitting him over the head with one of the Journals. He yells for Dipper to wait, Dipper demanding a reason why as he pulls the Journal up, ready for another hit. The person says his reason is two questions, telling Dipper that more question than answers are to be expected when dealing with the unknown. Dipper starts to realize something as the person pulls something out of his jacket, asking how they know his brother as he shows them the picture Mabel took just before Gravity Falls was destroyed. Dipper pulls out his phone and shines the light on the youthful face of Stanford Pines as he shows off his six-fingered hands and asks if they have seen the Journals around anywhere, Soos taking this as his cue to pass out.
In a fancy hotel room somewhere, Drew, Maureen and Rushtar are watching the Guardsman pace back and forth, a death grip on the phone that refuses to connect to whoever he is calling. He tells his students that, despite him knowing they would never use magic, he knows he just heard Dipper calling to him, and he knows Dipper would never joke about his sister being in danger. Drew tries and fails to assure the Guardsman that the twins and their friends can handle anything before mentioning that they can't do much as they don't have teleporting capabilities. The Guardsman agrees that they don't as he walks out onto the balcony, his confused students watching him. He tells them to go to the safehouse if he's not back by the next morning, and before they can respond, he jumps off the balcony and flies away, leaving his students to stare after him in shock.
EZB's death is turning into a spooky scary skeleton while he sings the cryptogram, which decodes to:
When the crypt doors creak and the tombstones quake
Soos retreats from his undertake
Dippers plans compound in size
Mabel's fate shifts to demise
Island tide will swallow you alive!
Now don't close your eyes and don't try to hide
Or Wendy's head may be strung up-side
Stanford now shows just in time
Schemes yet made may be sublime
Which side is he? Maybe help or crime!
As the moon climbs high over dead Oak Tree
Soos and Dipper prepare with he
Rescue, hope, and more to try,
aid may come yet from the sky
Grim grinning ghosts come out socialize!
With fists and spells you go raising hell
Fight for family with all rebel
Yet found yourself outmatched inside
Secrets lost prove classified…
If you'd like to solve the pain of fate
Of those lost old souls in their old estate
Find their center and balance thee
Maybe all can smile in glee
So hurry up, or you'll find your destiny.
