Some dumb teenagers are celebrating Halloween big time; one of them, with a piggy mask, for no apparent reason, decides to show off his huge naked rear to an elderly man (Harold Ayer) who is slowly going back to his home. The old man swears about the teenagers. Somebody is lurking in the shadows and approaching him: it's a handsome young man who scares him with a fake rat. With the scare, all the convenience store items which the old man has bought, fall to the ground. A pretty female teenager offers to help the old man, but he scares her away with a torrent of insults; when he is left alone, the old man laughs threateningly, saying that all the damn children will be sorry, and he picks up first a red apple and then some Gillette razor blades.
The girl, Judy (Cathy Podewell) arrives home in anger and slams the door. She asks her mother (Karen Ericson) whether Jay (Lance Fenton) has called her, and her mother says he didn't. Sal (William "Billy" Gallo) has been the one who called, but Judy is not interested in him. When Jay finally does call, he tells her that her efforts to get money for the poor are useless and that they have changed their plans to enjoy the night, so that they will go to Angela (Amelia "Mimi" Kinkade)'s party instead. Judy dislikes Angela, but she finally changes herself and decides to go. Jay tells her that they will go to Hull House. While she is undressing, Judy's little brother Billy (Donnie Jeffcoat Jr.) scares her with a monster's mask, jumping from inside her closet. He mocks her boobs, and goes to unlock the door: somebody has rung the bell. When he opens it up, nobody is there. A side door opens, and it's Sal who scares the boy. He tells the boy to call Judy, but he tells the news: Judy is going out with Jay. Sal leaves for Hull House with the boy's monster mask.
Meanwhile, Angela steals a sackful of things from the local convenience store while her friend, sexy bombshell Suzanne (Linnea Quigley) distracts the male shop clerks (James W. Quinn & Clark Jarrett) showing them her panties. Jay picks Judy up. The piggy boy, nicknamed Stooge (Hal Havins) causes his two friends, Rodger (Alvin Alexis) and sensible Helen (Allison Barron) - who was driving - to blow a tire out. Fortunately, they are already very close to Hull House. The girl says that nobody would organize a party in such a place, but Stooge says that everything is OK. The car full of party-goers mock the stranded teenagers. They arrive to Hull House, which used to be a funeral parlour. They comment that a family member got mad and he killed all his relatives and then committed suicide. The place has been the theme for boogeyman stories to the local children and horror legends for years and years.
Judy, Jay, Max (Philip Tanzini) and Frannie (Jill Terashita) are the first to arrive, but the place is cold, dark, shrouded in mist and looks deserted. Max mentions that there is a river underground, and that the high wall was built to keep evil spirits away, as they can't cross water. He also points that nothing can be heard, not even crickets. Somebody is watching them from behind the window.
Jay wants to hide inside a coffin to scare the stranded friends, who have just arrived; when he opens the lid, Sal is inside wearing Billy's monster mask, scaring Jay. The party begins right away. When the batteries of the radio become dead, Angela proposes to celebrate a seance. They push Rodger and Stooge into another room, and they find a huge mirror. Rodger looks dizzy about that. Rodger is the only one who doesn't sit in front of the mirror. When they all - except Rodger - concentrate, the mirror's image fades to black. Helen sees the head of a monster, and also the severed head of a man who looks like a pirate pushed against the mirror. Helen panics and starts whimpering, while the mirror falls to the ground. They all look to the pieces of broken window glass, and some knocks are heard. Nobody has invited anybody else, but Suzanne (Linnea Quigley) wishes that a good-looking stud appears. Judy thinks that the thuds come from the basement. There, the monster Helen saw pushes open a vault-like door.
Nobody can see the monster moving: it's become a powder which gets into Suzanne. Angela recognizes the signs of devil's possession: a stench, sudden cold and an unexpected breeze. Everybody disregards her opinion. Suddenly, there is a perfume of roses. Angela says that the house is not haunted from ghosts but possessed by a devil. Rodger and Helen want to leave, but they have no car. Suzanne gives them Angela's car keys. After they leave, Jay and Judy want to investigate the house to find some private place. Suzanne stays with Stooge and Sal. Stooge and Suzanne leave together, and Suzanne enters a room. She bangs the door on Stooge's face, who is scared by the sudden wind and breaks his flashlight.
Frannie and Max want to leave Jay and Judy alone, but she is not in the mood for sex, as the house scares her deeply. Meanwhile, Helen and Rodger can't find the door in the wall which they entered through. Helen thinks that they are all already dead and that they have gone to hell. She suddenly disappears, and Rodger gets scared. The house calls his name, so he locks himself inside a car.
Jay is trying to convince Judy to have sex with him, but they argue because Judy went out with Sal once. Jay leaves in anger, leaving Judy locked inside the room.
Stooge hasn't realized so far that Suzanne has become a monster. Angela is with Sal, and she contorts like an animal in heat. Music blasts from the radio. Sal tries to leave, and comes across Stooge, who takes Sal's place and kisses Angela, who bites off his tongue.
Jay finds Suzanne, who is applying make-up to herself as usual, but he says he wants to go home. Suzanne's demon voice (James W. Quinn) argues that he's already at home. Jay comes back to Suzanne, who seduces and kills him. Meanwhile, Sal finds Angela burning her hands. Sal tries to run away.
Rodger wakes up in the car, but he leaves it when he sees the dead body of Helen. Suzanne blinds Jay because he tells him to "stop staring at her". Monster Stooge attack Frannie and Sal, who were doing it in the coffin. Stooge breaks Frannie's neck and encloses her with Sal. Angela welcomes Rodger back into the house, who bumps onto Sal.
Monster Stooge tries to get to Judy, but can't. Finally, Sal frees Judy, who hugs him. They run away from Angela and find Suzanne, who is still holding to Jay, and propose an orgy. Judy runs away, but all the doors close in front of her. She decides to run upstairs.
Judy reaches the rooftop. As Stooge approaches, she has to go there. Judy finally falls down - we can see Jay completely dead - and falls on top of Rodger. Stooge threatens them. When they run away from him, they see Angela - they also see Sal Romero's tomb, who died on this Halloween night. They run through corridors and corridors, with Angela floating after them.
They reach the basement and find the vault. Rodger proposes to pray, but Judy says she has been praying all night. They get inside and leave devilish Angela and Stooge outside, threatening them. They are about to unscrew all the screws of the vault, but Judy has an idea: she creates a flame-thrower. That gives them the opportunity to run and leave the vault.
However, when they are about to pry open the door, Jay appears, threatening Judy especially. Angela and Jay join sides, and move menacingly towards them. Rodger jumps through a window; Judy follows through.
As there is no door in the wall, they have to climb it. For Judy, it's a difficult task, so Rodger goes first and then tries to pull her above the wall. He finally has to let go of her, when all the dead people appear. Finally, Rodger saves her, going up onto the wall again, just when she is about to give in.
All the dead monsters, including the first one, turn to dust, because the sun is rising.
When Rodger and Judy are dragging their feet back home it's already the morning of the following day. They go past the house of the old man at the beginning of the film, and he mutters that they are disgusting people who are coming back from a party. The old man picks up his newspaper and goes back in his home. There, his wife (Marie Denn) has already prepared him his breakfast. He grumbles that there's nothing nice about the day, and that the food is not bad.
They talk, and the wife says that she's been awake for hours, so that she decided to make some home-made apple pie as he bought so many. At that moment, the old man stops eating. He feels something strange: his neck is cut open from the inside, and one of the razor blades slides outside among a spring of blood. The old man dies a painful dead.
His wife / widow approaches him and kisses him on his head tenderly, wishing him a happy Halloween.
Cut to credits.
...written by KrystelClaire.