Haunted by the lack of gossip in the school, Spectra searches for news for her blog. Angered by her punishment for plagiarizing an essay with being suspended from the Fear Squad, Toralei tells her a rumour about the werewolves of the school having were-fleas. As the rumour sends the students into chaos with staying clear of the Wolf siblings, Spectra observes what she has caused. A short while later, Draculaura begins to experience hauntings, with her locker acting strange, finding herself talking back to Mr. Rotter out of turn, and someone changing her hairstyle.
Clawdeen confronts Spectra about her post, and urges her to find truthful material. However, she flees when Draculaura, Twyla, Rochelle and Sirena ask her about the hauntings. They follow her to the attic, and watch as she unlocks a door and disappears into it. Still following her, the ghouls find themselves on a skiff, piloted by the daughter of the Grim Reaper, River Styxx. With her father away in Las Plagueas, River has the boat to herself, even installing confetti cannons onto it. Spectra appears and is shocked by their presence, and explains about the Ghost World, where most ghosts live due to the stigma of their hauntings. River explains that the boat is taking them to Haunted High, Spectra's old school.
River asks what brings them here, and Draculaura explains her hauntings. River finds that impossible, as there hasn't been a haunting since the notorious Red Lady, a ghost who could move easily between the Ghost and Monster (solid) worlds, until she was apprehended and imprisoned to work off her crimes. The boat falls prey to a pirate ship, the Salty Spectre, led by the ghost pirate Vandala Doubloons, and her pet cuttlefish Aye. However, Vandala becomes seasick and fears the "solids," residents of the monster world. Dressing in reaper robes, the ghouls enter the school (although the doors must be opened instead of phased through due to the ghouls being solid and not ghosts).
Spectra reminisces in her old school, but is shocked to see the number of students draped in detention chains, handed out by Principal Revenant and the Ghosts of Hauntings that serve as the Hall Moanitors. They go to the creepateria to find out the perpetrator of Draculaura's hauntings. There they meet Spectra's old best friend, Kiyomi Haunterly, daughter of the Noppera-Bo, the faceless ghost, who has gone from the shyest to most popular ghoul in school. Draculaura seems to be familiar with Kiyomi, but she rebuffs this and flies away. Their attention is then drawn to Porter "Paintergeist" Geist, son of a poltergeist, who is vandalizing the creepateria with ghost paint, which evaporates quickly, though the students cheer him on as he does it. The Hall Moanitors catch him in the act, and shackle him after he crashes into Spectra, who thought to find a scoop in the ordeal. When Spectra explains she is not a student at this school and is from Monster High, Revenant has the rules changed, and unveils her friends as solids. They flee, pursued by the Moanitors, who discover the chains do not work on solids. They safely arrive back at Monster High, but Spectra is chained and dragged back to Haunted High.
To get back into the ghost world Twyla takes them to the Boogey Mansion, to look for the right Boogey Sand to turn them into ghosts so they can move around the ghost world undetected, especially since she knows which Boogey Sand will return them to their normal selves afterwards. In the process, Rochelle is accidentally turned into a blob monster, before Clawdeen sneezes the right powder over them and they turn into ghosts, although floating is harder then it looks.
Dragged into Revenant's office, Spectra asks about the hauntings, which the principal denies. She is given 10,000 essays to do twice as her punishment, which she takes in her stride as she loves writing, something which greatly puzzles Porter. Spectra and Porter begin to bond, and when Porter questions all the rules and detentions, he and Spectra decide to investigate. Meanwhile, the Hall Moanitors move into Monster High and begin to seize the ghost students at the school, such as Operetta, Scarah and Johnny. Re-arriving at Haunted High, the ghouls meet Vandala and Kiyomi, who help them to control their ghost forms. Rochelle especially enjoys the freedom with this form, and dives into the school pool.
Having found no information about Revenant in the library, Spectra and Porter return to the school main hall, and are horrified to find numerous Monster High students chained and being greeted to Haunted High by Revenant.
Overhearing ghost students talk about how solids want to haunt them Spectra becomes outraged, labeling the talk as stupid gossip. Spectra realizes this is the exact sort of gossip she spreads, and how it is hurtful. The Moanitors behaviour escalates, and they begin to give out chains for seemingly no reason at all. When this happens to Kiyomi, the ghouls go to protect her, bringing them to Revenant's attention. Seeing how the ghouls have become ghosts, Revenant demands to know how they did so, and when they refuse, gives the Moanitors permission to shackle them. Kiyomi protects Draculaura and Porter takes them to a safe room only he knows of. Spectra admires the artwork, and Draculaura comes to the realization that Kiyomi is the one who has been spying on her. Kiyomi feels bad for this, and when Spectra announces her intention to confront Revenant, Porter pleads with her not too, drawing the attention of the others.
Spectra eavesdrops on Revenant's plan to get more students stuck at Haunted High, and is discovered by one of the Hall Moanitors. Revenant questions Spectra, until Porter appears and distracts her, giving Spectra a chance to escape, although it means Porter is heavily chained. She forces him to reveal their hiding place by tightening his chains, and the Moanitors capture all the ghouls, causing Spectra to be angry at Porter for selling them out. However, Porter reveals he stole the keys to the chains, and transfers all the chains to himself. While Porter had stolen something, so had Revenant, the item being the note book Clawdeen was using to document their journey to give to Spectra for her blog, to use as a true story instead of gossip. From this she discovers the Boogey Sand, and the Moanitors take off on River's yacht to find it. Now freed, the ghouls pursue them on Vandala's ship after rescuing the rest of the Monster High students incarcerated at Haunted High.
Spectra stays behind however, to hear Revenant's announcement, and her intention to use the Boogey Sand on solids as revenge for making the ghosts fear them. Spectra seeks solace in the library and suddenly realizes Revenant is the Red Lady of legend, as she sends the Hall Moanitors to do her work and never leaves the building.
Kiyomi opens a portal and they beat the Moanitors to MH, who begin to unleash Boogey Sand via confetti cannons on the Monster High students. Vandala boards their ship however, and retrieves the sand. Back at HH, Spectra reveals that Revenant is the Red Lady. Taking this in her stride, Revenant seizes the key, and sends all the chains flying at Spectra.
Chased by the Moanitors, Kiyomi attempts to open a portal to send them back to the ghost world, and with the help of the others and their ghost powers, is successful. The yacht appears as Revenant's sends her chains flying, and they entangle the boat and Moanitors. Finally free of her chains, Revenant opens a portal and attempts to enter the Monster World. but finds that she still can't leave as more chains automatically appear on her. Revenant looks to blame someone for keeping her there, but Spectra tells her that she's done this to herself. Because every unjust detention and unfair punishment she gave out, every rumor she spread and every lie she told, only served to wrap her in more chains as it warranted more punishment for herself. Revenant tries to deny this at first, but Spectra points out that deep down, Revenant must've known that what she was doing was wrong, and suspects that her chains were generated by her own conscience, continuing to punish her for her crimes against her students. Seeing the error of her ways, Revenant repents, and takes back the chains, her first good act. Porter congratulates Spectra for her heroism, and the ghost students see how gossip is wrong. Inspired by this, Spectra decides it's time for the students to get to know each other, and they throw a party at Monster High. Revenant works to get rid of her chains, and the werecats catch sea-fleas aboard Vandala's ship.
Spectra and Porter paint the boat to announce their new relationship, and the movie concludes with the Hall Moanitors cleaning up River's boat and playing with the Boogey Sand, even after being caught by Twyla.
- Why would Porter know of a secret room "no one else" knows of within Haunted High when the building originally was Revenant's home? Does even Revenant not know of it?
- When Heath says he heard that Slo Moe didn't come to school because he had geiss lice, a bit before that, Slo Moe is walking in the hall behind Clawdeen.
- When Toralei told Spectra that she was suspended from the fear squad for a month for plagiarism, this contrasts with her quitting the squad in Scream Building, along with the Werecat twins. She was returned to the squad when Nefera was team captain and had cut the original squad, but nothing aside from the aforementioned line in this special has indicated that Toralei is still on the squad now that Cleo and friends are back.
- This special was originally named Haunted Halls.