Slimer leaves home after Peter yells at him for eating Winston's birthday cake, and the Ghostbusters set out to find him. But more problems arise when Egon discovers a poltergeist feeding off the power of ghosts in the local area; who only needs one more ghost to reach his full power.

The guys are hired by a pair of young siblings to rid them of the Bogeyman, an entity Egon is quite familiar with.