Peter, Ray, and Winston step in to help Egon, who has been cornered by a bunch of multicoloured ghosts, but doesn't seem to mind. Using a PKE meter, Egon determines that the ghosts are being controlled, and a disembodied voice promptly compliments him on his induction, prompting a vortex to appear. Out of the vortex come flames and a purple demon. The demon calls himself the Master of Shadows and compliments Egon on his intellect, then the Ghostbusters try to fire at him but he teleports away and calls the proton packs primitive and ineffectual. Then, he threatens to burn down the city before disappearing.
When they get home, Egon builds a device he thinks will allow him to communicate with the Master of Shadows, reasoning that they need to know their enemy in order to defeat him. The device works, and Egon has a sass-off with the Master of Shadows before challenging him to a duel at midnight.
After the communication ends, Slimer starts poking at the machine, and it zaps him, then it zaps Egon too, and ends up with Slimer wearing Egon's glasses and Egon unconscious. He wakes up, but has a strange expression on his face, and then Slimer starts talking in Egon's voice. It turns out that the two have swapped bodies.
While Slimer-as-Egon eats, Egon-as-Slimer explains that the accident happened as a result of Slimer's ectoplasm causing a short circuit, therefore they need to fix the faulty circuit to reverse it. They then get a call, so Peter, Ray, and Winston head out, leaving Egon and Slimer at home.
They chase after some ghosts at a roller rink, and at one point they haunt some rollerskates and cause Winston to skate around against his will. The ghosts chase, so Peter and Ray don't want to fire for fear of hitting him, so Peter tells Winston to go faster. Once he's ahead of the ghosts, Peter asks him to shoot the skates, which he does. Once the ghosts are trapped, the Master of Shadows appears, wonders where Egon is, and reminds them of the deal they made.
They arrive home to find Egon having trouble being in Slimer's body. He tells them that he's determined which circuit needs to be rewired, but he can't do it himself due to the ectoplasm on his hands. While Ray tries to fix the machine, the others try to go out and work, which Egon has trouble with in Slimer's body. The Master of Shadows then appears in front of Ray and Slimer-as-Egon and declares that the duel will be moved to right then. While Ray contacts Peter, Slimer-as-Egon runs off, so the rest give chase in the car, with Ray bringing the fixed machine.
Once they catch up, Slimer-as-Egon is facing up to the Master of Shadows, and Egon-as-Slimer flies around and distracts him, while the others set up the machine. They successfully switch Egon and Slimer back, then trap the Master of Shadows. The next day, Egon and Slimer prank the others by pretending they're still switched.
This episode provides examples of
- Curious as a Monkey: The impetus for Slimer being zapped by Egon's machine is that he was curiously prodding at it.
- Dark Is Evil: The episode features a scary, evil demon who calls himself the Master of Shadows.
- Delicious Distraction: While in Slimer's body, Egon gets distracted from his job by a bakery.
- Did You Just Flip Off Cthulhu?: The Master of Shadows is a powerful demon, but that doesn't stop Egon from bragging to his face about being smarter than him. Exploited when he uses this as part of his challenging the Master of Shadows to a duel.
- Ectoplasm:
- Discussed. Apparently, Slimer's ectoplasm was what caused the machine to short-circuit, which means that he can't fix it himself with ectoplasm on his hands.
- Played for laughs when Egon in Slimer's body tries to pick up a notepad, only to get it stuck to his hand with ectoplasm.
- Evil Laugh: When Egon uses his communication device, the Master of Shadows laughs maniacally.
- Food Coma: Discussed when Egon says that they need to undo the body-swap before Slimer eats his body into a coma.
- Full-Name Basis: The Master of Shadows addresses Egon by his full name.
- Loud Gulp: Ray fearfully gulps when the Master of Shadows appears.
- Mythology Gag: Peter calls Slimer "Spudface", a reference to Ray calling him an "ugly little spud" in the movie.
- Not Hyperbole: When Egon is in Slimer's body, he says to the others, "You look like you've seen a ghost".
- Not So Above It All: Egon, despite usually being very serious, actively sasses the Master of Shadows, and at the end, pranks the rest of the Ghostbusters.
- Not So Stoic: Egon may usually be The Stoic, but he's still part of a Reactive Continuous Scream at one point.
- Ow, My Body Part!: Shortly after entering Slimer's body, Egon says, "Oh, my head!".
- Questioning Title?: The episode title is a question mark.
- Reactive Continuous Scream: When a teenage boy sees Egon-as-Slimer, they both scream at each other several times.
- Red Eyes, Take Warning: The Master of Shadows is a red-eyed, ghost-controlling demon.
- Say My Name: Ray shouts, "EGON!" when Egon falls unconscious.
- Shock-and-Switch Ending: At the end, it looks as though Egon and Slimer are still switched, but they're just kidding.
- Snarking Thanks: Egon-as-Slimer insincerely "thanks" Peter for calling him an "ugly green smear".
- Speak in Unison: When Egon and Slimer swap bodies, the other three Ghostbusters say, "Oh no!" in unison.
- Spell My Name with a "The": The demon is named the Master of Shadows.
- Tastes Like Chicken: Exaggerated. Apparently, everything tastes of chicken to Slimer.
- Teleportation: The Master of Shadows dodges the proton packs by teleporting.
- Throwing Off the Disability: When Slimer is in Egon's body, he seems to have normal eyesight, since he gets around without Egon's glasses.
- [Verb] This!: When the Master of Shadows says he applauds Egon's ability to discover his presence, Venkman, before attacking along with the rest of them, says, "Well, applaud this!".
