In Xander's basement he, Willow, Oz and Buffy are carving pumpkins in preparation for Halloween. Xander reveals that he has rented a movie for them for Halloween, but instead of Phantasm, the video store gave him Fantasia. Willow mentions their plans to attend a fraternity party, leaving Xander feeling left out. They tell him he can come and they all notice that Buffy is still depressed over what happened with Parker.
Later at Sunnydale U, Willow is discussing her magic with Buffy when Oz approaches and mentions his worries over Willow's magic. When Buffy sees Parker, she feels. Willow catches up to her and tells her that they'll have fun at the party, but Buffy is sure she's going to have to patrol.
When Buffy reaches Giles's home, she finds him dressed for Halloween in a pancho and sombrero and his house decorated. She asks if she'll need to patrol, but he reminds her that creatures of the night stay in on Halloween, finding the holiday far too crass.
At the Alpha Delta fraternity house, two of the brothers discuss calling Oz to help with their sound system.
Xander is preparing to go out when Anya comes to visit. She is wondering why he hasn't called when he reminds her that she said she was over him. She only said that because she thought it was what he wanted to hear. Xander lets her know that he tends to take things at face value and accept them. He does say that seeing her is a good thing and she wants to go out for their anniversary. It's been one week since they copulated. He lets her know that he has plans that night with Willow, Buffy and Oz. She doesn't understand why he hangs out with them since they have little in common. He invites her to the party, telling her that she needs to find a scary costume.
Having missed class, Buffy goes to see Professor Walsh to get the day's assignment. The professor tells Buffy that if she misses one more, she'll no longer be in the class. As Riley hands her the work, he tells her that he's noticed her lack of participation lately. He thinks she needs to go out and have some fun.
At the Alpha Delt house, Xander helps Oz set up the sound system for the frat house. One of the brothers is painting a symbol on the floor in preparation for the party. When they find out that Xander is not a student, he once again feels left out. When fixing the sound system, Oz cuts his finger and bleeds on the symbol. A fake spider on the ground near it suddenly becomes real, though no one notices.
At the Summers house, Joyce is helping Buffy with her Little Red Riding Hood Halloween costume. They reminisce about when Buffy was younger and her father would take her trick-or-treating. Joyce tells her daughter that it took some time after the divorce before she'd open up to people, but now she's got a good group of friends in Sunnydale.
At the dorms Willow is preparing to go to the party, dressed as Joan of Arc.
At the Alpha Delt house, one of the brothers shows a girl around the haunted house. She picks up the pealed grapes, intended to feel like eyeballs. When she opens her eyes, she finds that they are real eyeballs.
Buffy and Xander are the first to arrive for the party and she reveals that she brought weapons, just in case. Xander also has a plan just in case they get turned into their costumes again. He's dressed in a tux as James Bond. Buffy tells him that should they turn into their costumes again, he'll probably end up as cool head waiter guy. Willow and Oz arrive and Willow explains her costume. She was nearly burned at the stake and has a close relationship with God. Oz reveals a nametag on his shirt saying, "Hello, my name is God." As they walk towards the party, a group of commandos pass them. Xander tells everyone that he's invited Anya, leaving Buffy feeling left out.
In the house, the partygoers are running around, terrified.
Buffy and everyone walks in, not finding the party very scary. They go through more of the house and find a live tarantula crawling on Willow's shoulder and real blood on the floor. They hear a voice rumbling through the house, demanding to be released.
Anya arrives, dressed in a white and pink bunny costume. She finds no front door and when she steps away from the house to get a wider look, she sees a girl screaming from a window. The window suddenly disappears from the house and Anya runs off.
Back in the house, the gang finds themselves lost and wanting to get out of there. They come across one of the brothers, Chaz, cowering in a closet. As they question him, Buffy is attacked by a plastic skeleton with a knife that briefly came to life. She says she's fine and when they look back, the closet Chaz was in is now gone.
Giles is sitting at home, still in his costume and with a bowl of candy. Anya's comes by and tells him that Xander is trapped. Giles asks about Buffy, Willow and Oz and Anya tells him that they're there too, but they need to save Xander. Giles checks a few of his books before going to the Alpha Delt house with Anya.
In the house Willow and Buffy are arguing. Buffy wants them to find a way out while she searches for the cause of the problems. Willow wants to stay behind and use a spell to get every one of them out of there. Buffy expresses skepticism over Willow's magic, upsetting Willow. Willow storms off with Oz following. Buffy is left with Xander, who tries to soothe her, but she can't see Xander. She thinks he's run off.
As Willow and Oz walk through the house, she's still upset with Buffy. He stops her when he realizes that he's changing into a werewolf even though it's not a full moon. Oz leaves Willow there, not wanting to hurt her.
Xander finds a mirror, noticing that he can see himself even though no one else can. A severed head behind him comes to life and tells Xander that he can see him.
Oz is hiding in a bathtub, trying to talk himself out of changing.
Willow has found a table and is sitting, trying a spell that will lead her to her friends and out of the house. It works, but as she gives the speck of light more and more instruction, it multiplies, swarming over Willow.
Buffy is looking through the house and finds herself in the basement. One of the frat brothers is in there, his head at an odd angle. Demons come out of the ground, trying to pull at Buffy. The frat brother tells her that her friends have all run from her, but she's not alone.
Outside, Giles and Anya inspect the wall where the door should be. He says he will have to create a door and pulls out a chainsaw.
Buffy manages to get away from the frat brother and the basement. She goes through a door and finds herself upstairs. She notices Oz in a corner and Willow runs in, yelling for the specks of light to get off of her. The room is filled with terrified partygoers. Buffy mentions that they're not okay and Xander, who is also there, says that he'd offer his opinion but no one can see him. He then discovers that he can be seen now. They pick up the book that Oz and Xander saw the brothers getting the symbol out of earlier. Willow translates the Gaelic and finds out that it's the mark of Gachnar, who is causing their fears to manifest. They decide to get everyone out of the house when they hear a rumbling. Giles comes in, chainsaw in hand, with Anya following.
Giles tells them that the walls closed up behind them. He takes the book from Willow and reads. He shows Buffy the illustration of Gachnar and she's intimidated. He reads about destroying the mark of Gachnar and before he can finish, Buffy destroys it. However, Giles tells her that destroying it won't stop the demon, but bring it forth. From the ground, a demon arises, reaching about half a foot tall.
They watch as Gachnar tells them they should fear him, he is the dark lord of nightmares. Willow finds him cute and Xander taunts him, prompting Giles to reprimand Xander. Buffy brings her foot down, stomping Gachnar and killing him.
Back at Giles's, they eat his Halloween candy ad Giles researches the book. Xander questions Anya's costume and she tells him that bunnies frighten her. Giles reads the text below the illustration of Gachnar and realizes he should have read it earlier. It says, "Actual size."