The Ghostbusters' old "pal" and nemesis, Walter J. Peck, ex-EPA hatchet man extraordinaire, is back from the Gozer incident, and he's trying to raise some trouble with the Ghostbusters again. First he tries to get them arrested for illegal trespassing by calling in a phony ghost alert at a military base in Queens, but after that backfires, Peck joins up with BUFO (Bureau of Unidentified Flying Organisms), and takes Slimer with a court order. After some tests, Peck deems Slimer a hazard case and plans to destroy him with a cyclotron, forcing Ghostbusters to save Slimer from Peck.