Three odd-ball scientists get kicked out of their cushy positions at a university in New York City where they studied the occult. They decide to set up shop in an old firehouse and become Ghostbusters, trapping pesky ghosts, spirits, haunts, and poltergeists for money. They wise-crack their way through the city, and stumble upon a gateway to another dimension, one which will release untold evil upon the city. The Ghostbusters are called on to save the Big Apple.
Before they are kicked out of the University, their first investigation is a haunting at the New York City Public Library and after seeing some symmetrical book stacking they encounter a ghost (the Gray Lady) that runs them out of the Library. Before they can share news of their discovery, they were terminated from conducting any research at the New York City University.
The Ghostbusters decided they would take matters into they own hands and they start an business named "Ghostbusters", a "professional paranormal investigation and elimination service", out of an old firehouse, using a 1959 Cadillac Miller-Meteor Ambulance dubbed "Ecto-1" to get about the city and hiring Janine Melnitz (Annie Potts) to handle the phones and clerical work. Dana Barrett (Sigourney Weaver) of 55 Central Park West, comes to the Ghostbusters and asks for their help after she experiences some horror in the kitchen of her own home. The Ghostbusters do a few tests to determine that she isn't crazy as she recounts a paranormal experience in her kitchen centering around the name "Zuul". Peter seizes the opportunity to get romantically closer to Dana, and goes with her to the apartment. Using the Ghost Sniffer he checks out the place, finds nothing in the main room, and bedroom. Dana then directs him toward the kitchen where he finds eggs that cooked themselves on the counter, but gets no readings on the Ghost Sniffer despite using it correctly.