Scooby-Doo [Don Messick], Shaggy Rogers [Casey Kasem], and Scrappy-Doo [Don Messick] head to Miss Grimwood's Finishing School for Girls, where they are hired as gym teachers, mistaking the gig for a simple assignment before discovering a far more unusual and magical purpose behind the school. The place, led by the stern yet fair Miss Grimwood [Glynis Johns], isn’t just a typical academy: it’s a haven for daughters of famous paranormal families. Among the students are Sibella Dracula [Susan Blu], the refined daughter of Count Dracula; Elsa Frankensteen [Pat Musick], the brave daughter of Frankenstein Senior [Zale Kessler] who also doubles as Frankenstein Senior’s fearsome presence in the castle lore; Winnie Werewolf [Marilyn Schreffler], the scrappy child of the Wolfman; Phantasma [Russi Taylor], the translucent daughter of a phantom who goes by the nickname Phanty; and Tanis the Mummy [Patty Maloney], a playful, pyramid-inspired heroine named after an ancient Egyptian city. Rounding out the school’s peculiar crowd are a floating disembodied white hand known as the Doorbell Monster [Linda Gary], a cleverly discreet octopus butler, a two-headed shark that patrols the moat, and Legs, a helpful spider that lends legs to the upcoming volleyball match. All of them share a surprising warmth with the school’s colorful staff, especially the tiny dragon Matches [Frank Welker], who serves as a curious, protective companion to the girls.
At first, Shaggy and Scooby feel out of place among so many monsters and myths, but the girls quickly take a liking to them, and the pair gradually settles into their roles as gym instructors. The school’s daily life is punctuated by quirky routines, flashy sashes of school pride, and the looming presence of the headmistress’s strict but fair regime. The students’ unique backgrounds create a sense of camaraderie and misfit charm that helps the trio loosen their guard and embrace the unexpected family they’ve found among the Grimwood Girls.
The calm is disrupted during the annual volleyball match against the neighboring Calloway Military Academy. The Calloway cadets—Jamaal [Bumper Robinson] and Tug Roper [Scott Menville]—cheat by rigging the volleyball with a remote control. In a goofy, chaotic twist, Scooby accidentally swallows the remote, effectively letting the girls win the game and exposing the boys’ dishonorable trick. The victory is bittersweet, because it foregrounds the underlying tensions between the two groups and foreshadows the looming conflict between the girls’ world and the cadets’ expectations of strength and supremacy.
Halloween night brings an open house that turns into a warm, if guarded, exchange between the girls’ fathers and the Grimwood community. The cadets’ father figures—led by the friendly Colonel Calloway [Ronnie Schell]—arrive with a polite, protective air, showing kindness and respect toward the girls, despite the night’s spooky aura. The gathering reinforces that this is a place where monsters and humans can coexist with dignity, and it gives Shaggy and Scooby a sense of reassurance about the girls’ safety. Still, under the surface, a power-hungry witch named Revolta [Ruta Lee] plots to kidnap the students and bend them to her will, aided by her ominous minion, the Grim Creeper [Andre Stojka]. Revolta begins by hypnotizing Shaggy and luring the girls on a field trip to the treacherous Barren Bog, where matches of courage and fear will be tested. Matches wants to come along, but is told to stay behind, a decision that foreshadows the danger of underestimating Revolta’s reach.
Elsa and Tanis, with their quick wits and bravery, help rescue the Cadets who fall into quicksand during the bog excursion. Revolta’s spider bats begin to systematically capture the girls, while Revolta works on a potion designed to turn the girls evil at midnight. The plan hinges on turning the school into a fortress of darkness, where Revolta’s magic and minions would enslave the Grimwood Girls. Sensing the peril, Scooby, Scrappy, Shaggy, and Matches—together with their new allies—races toward Revolta’s looming castle to put an end to the plot.
Inside the castle, the heroes confront a series of supernatural challenges: a shape-shifting Mirror Monster that mimics the bad versions of those who gaze into its mirror, a colossal Well Dweller that poses a grave physical danger, and Revolta herself, whose power intensifies as the clock approaches midnight. As the midnight moment arrives, Revolta unleashes a potion through hair-dryers that would instantly corrupt the girls. In a twist of fate, Scooby and Shaggy inadvertently reverse the potion’s effects just as Elsa hurls Revolta’s wand into the potion, causing a spectacular explosion that reshapes the room and frees the captives. The Cadets, moved by the Girls’ bravery and the friends they’ve formed, arrive just in time in a pedal-powered helicopter, rescuing everyone and thwarting Revolta’s final plan.
The school erupts into a triumphant celebration, with the Grimwood Girls and the Cadets throwing a party to honor the heroes who saved the day. Though the students are now more confident and resilient than ever, Shaggy and Scooby—still part of their own universe of fright—remain quivering at the thought of new monsters joining the school next year. As the party winds down, the group shares one last werewolf howl goodbye to the girls and Matches, who wave back with bright smiles from the school’s gates. The trio’s departure signals a blend of relief and wonder at the strange, wonderful world they’ve discovered, leaving the Grimwood Girls to forge their own destinies while the world outside continues to harbor a taste for mystery, adventure, and friendship.
