In the leadup to Halloween, many ghosts have been rising, creating a lot of work for the Ghostbusters, and a woman named Cynthia Crawford reports it on the news. At the firehouse, Winston is concerned, since the last ghost they fought was tougher than it should've been. Ray observes that not only are they getting more cases as Halloween approaches, they've been getting tougher. Peter goads Egon into telling him what he's been working on, and Egon reluctantly admits that he's determined that the increase in supernatural activity started when some ruins were brought to America from Ireland, that dated back to when Halloween was invented, and he's wondering if Halloween was inspired by a supernatural event.
At a museum, a goblin (who is with another one) draws an infinity sign on a closet, summoning a pumpkin-headed demon, who causes chaos around New York. Then (while Ray and Egon are building and Winston is trying to teach Slimer to play checkers) the same goblins show up disguised as trick-or-treaters and use their breath to blow Janine across the room.
The Ghostbusters go out and find a whole lot of ghosts, led by the pumpkin-headed demon, who then uses telekinesis to bring Slimer over. The demon announces a plan to make Halloween last forever, and when Slimer disapproves of this, he calls him a "traitor" and says that he will assist him or else "pay the price".
The ghosts continue to cause chaos, and the Ghostbusters trap them, but they've only caught a small amount of them. Then, Peter looks at his watch and finds that it's still midnight despite it feeling like hours have passed, causing Egon to conclude that time is slowing down. A TV news reporter reveals that other countries are being shrouded in a dark cloud, so Egon determines that a permanent Halloween is being made. A ghost shows up in a car, so the Ghostbusters try to trap it, but a brick wall gets in the way.
The pumpkin-headed demon arrives and they try to zap him, but miss. He asks why they're attacking his "little ones" and introduces himself as Samhain, a spirit of Halloween. He is said to be unstoppable, but when Peter suggests Samhain has low self-esteem, Egon gets an idea: turn on all the lights in the city, since (as he discovered when trying to look at him with his flashlight) Samhain hates light.
Unfortunately, the power cuts out, but Egon isn't daunted and walks off with a plan. While Peter, Ray, and Winston watch the ghosts, who are giving Slimer a hard time, Egon insults some goblins in a car, which he then separates from the strobe light it's towing with his proton pack. He gets two more strobe lights, then tries lighting them up with his proton pack, but it doesn't work.
Samhain tells Peter, Ray, and Winston to lower their weapons or he'll "do something unfortunate" to Slimer. Slimer starts fading away, but Ray saves him by getting him to come over by pretending he has pizza. Egon tries lighting the strobe lights again, and this time it does work. Samhain cowers and the Ghostbusters fire at him and trap him, ending Halloween, and the power comes back on too.
This episode provides examples of
- Animate Inanimate Object: Invoked when Samhain brings a statue and clock to life.
- Anthropomorphic Food: Invoked when Samhain brings some apples to life.
- Anthropomorphic Personification: Samhain says that he "is" Halloween.
- Blinded by the Light: When Egon says that light throws Samhain off, Ray (who was having Egon's torch shone in his face) says that it doesn't do him much good either.
- Blowing a Raspberry: Slimer blows raspberries at Samhain.
- Category Traitor: Samhain denounces Slimer as a traitor to their kind for living with the Ghostbusters and helping them.
- Comically Missing the Point:
- When Winston says, "I don't like this" (regarding a ghost being surprisingly hard to trap), Peter agrees, but thinks he's talking about the news broadcast and adds, "I always look terrible on TV".
- Peter again when he makes fun of Samhain's outfit and suggests he has low self-esteem, Egon says, "That's it!", to which Peter responds, "'That's it'? We should make fun of the way he dresses?!".
- Cut Phone Lines: After the goblins harass Janine, the guys get to work, and Egon detects all sorts of supernatural activity throughout the city. When Winston questions why no one called them, Ray suspects the phones have either been disabled or outright possessed.
- Cyclops: Some of the ghosts have one eye.
- Dem Bones: A few of the ghosts appear like skeletons.
- Did You Just Flip Off Cthulhu?: Peter Venkman insults and teases Samhain, who's a powerful, allegedly-unstoppable, demon who has power over the undead, several times. For example, at one point, he says to him, "When are you taking the next train out of town?".
- Evil Only Has to Win Once: Looking into the Containment Unit, Winston is surprised that Samhain is just sitting still and patiently waiting. As Egon and Peter noted:Egon: He waited 12,000 years to be free. He'll wait for his chance to come again.Peter: Which is not gonna happen, right, guys?
- Extra Eyes: A few of the ghosts have many eyes.
- A Father to His Men: Samhain sees all loyal ghosts as his "little ones" and will protect them from harm.
- Halloween Episode: This episode takes place around Halloween; fitting for a series about ghosts.
- Hero of Another Story: Samhain was trapped in those ruins 1,200 years ago.
- Humans Are Smelly: Samhain describes mortals as having a "stench" about them.
- Implied Death Threat: Samhain threatens to "do something unfortunate" to Slimer if Peter, Ray, and Winston don't lower their weapons.
- It's Quiet… Too Quiet: Lampshaded. While there wasn't any actual ominous silence, when the brick wall appears, Peter takes the opportunity to say, "It was quiet; too quiet" since he thinks the phrase is cool.
- Mundane Made Awesome: The contraption that Ray and Egon were working with suddenly breaks down and falls apart. It turns out that only one of them had a genuine scientific pursuit in all this.Winston: Um, not to pry, but what exactly is that thing you two've been working on?
Egon: A spectrum differentualizer.
Ray: A toaster.
Egon and Ray: Huh? - Mythology Gag: Peter calls Slimer a "spud," which is what Ray called him in the movie.
- The Night That Never Ends: Samhain and his minions try to make it nighttime 24/7 as part of the eternal Halloween.
- Nocturnal Mooks: Apparently, Samhain's minions (with the exception of Slimer, who seems to be mostly diurnal) come out at night.
- Not So Stoic: Egon yelps when Peter sneaks up on him.
- Oh, Crap!: Ray looks fearful upon realizing that Samhain is meant to be unstoppable.
- Papa Wolf: When the guys are chasing one ghost through the streets, Samhain personally intervenes by giving the little one cover and then attacking the team.
- Platonic Declaration of Love: When the lights turn on, Peter says "Egon, baby, I love you!".
- Properly Paranoid: In the run-up to the big night, Egon finds it troubling how routine cases have been tougher ever since the ruins were brought to the city. He worries what that portends, and he's soon proven right.
- Shock-and-Switch Ending: At the end, it appears like Samhain has escaped, but it's just Slimer in a pumpkin.
- A Storm Is Coming: One sign of the supernatural eternal Halloween is when a dark cloud covers many nations.
- Weakened by the Light: Samhain's weakness is light.
- Villainous Breakdown: Zig Zagged. Samhain takes being trapped badly, but he sits quietly in the Containment Unit in stark contrast to the other captives (who are thrashing about wildly).
- Villainous Crossdresser: Amid the ghost attacks, a couple ducks into a diner for safety. It's filled with ghosts dressed as humans, with the deep-voiced "waitress" taking the lead.
