With New York being plagued by power outages, the Ghostbusters set about to capture Killerwatt, a ghost who has the ability to possess electrical devices. But things take a turn for the worse when Killerwatt takes control of the city's power grid.
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.
An invasion of trolls emerge from the East River and take over the Queensboro Bridge, causing havoc for the citizens of New York. The Ghostbusters are soon on the scene to rid the city of the creatures, but are soon in a race against time to find a troll lost somewhere in the city, otherwise New York will be destroyed.
It is Halloween and New York is sent into chaos when two goblins release the spirit Samhain from a 7th Century relic. The Ghostbusters must work quickly to defeat Samhain & his minions and prevent the world from plunging into darkness forever.
Ray's heading back to his hometown to be the grand marshal in the parade; but when he's called to get rid of the ghosts in a haunted house and they get away, he starts to question his ability as a Ghostbuster.
Janine wants to go on a job with the guys and helps them catch a ghost. As payment, she takes a lamp that has a sinister genie in it that grants her the wishes of making her the boss over the Ghostbusters, and Egon fall in love with her.