The Ghostbusters are confronted by Crowley (Michael Rye) and his group, who want their help in ending Halloween. The guys turn him down, but one of their PKE meters is stolen and used by Crowley to accomplish his goal. Unfortunately, all he does is break a seal, opening our world to numerous ghosts – including the huge, rampaging Boogaloo (Brian O'Neal) – and giving the Ghostbusters a lot to handle on Halloween night.
A year after the Ghostbusters defeated Vigo the Carpathian, a ghost named Poso kidnaps Janine and Louis to force the Ghostbusters to hand over their business. The Ghostbusters get help from a recently-captured ghost, Shifter, to find out why Poso wants their business and where to find him. Covered in mood slime, Peter goes to the Ghost Town to save Louis and Janine.
Peter falls ill, and Louis asks a doctor (Stanley Ralph Ross) he met two days ago to come and take a look. It turns out the doctor has sent them potato chips, which makes people allergic to ghosts, and only Peter has eaten enough of them. The doctor gives them more chips. What the Ghostbusters don't know is that the doctor is a ghost and they have to develop resistance to the allergy.