After saving New York City from the demi-god Gozer, the Ghostbusters Peter Venkman, Egon Spengler, Ray Stantz, and Winston Zeddemore were sued by several city and state agencies for the property damage. Rather than face financial ruin, they accepted a restraining order barring them from operating as paranormal investigators and eliminators forcing them out of business. In the eyes of the city, they are now considered frauds.
Five years later, Ray owns an occult bookstore and works as an unpopular children's entertainer with Winston; Egon has returned to Columbia University to conduct experiments into human emotion; and Peter hosts a pseudo-psychic television show. Peter's former girlfriend Dana Barrett has had a son, Oscar, with a violinist whom she married then divorced when he received an offer to join the London Symphony Orchestra. In order to take care of her baby, Dana quit performing and now works as a restorer at the fictional Manhattan Museum of Art, working to prepare a malevolent-looking portrait of a legendary sixteenth-century tyrant named Vigo the Carpathian of Moldavia for an upcoming exhibition.
After an incident in which Oscar's baby carriage is controlled by an unseen force and drawn to a busy intersection, Dana turns to the Ghostbusters for help. Meanwhile, Dana's colleague Dr. Janosz Poha has become increasingly obsessed with the glowering image of Vigo in the painting and falls under its spell. Vigo, whose spirit inhabits the painting, orders Janosz to locate a child that he can possess, allowing him to return to life on the New Year. Janosz, infatuated with Dana, offers to bring baby Oscar to Vigo in exchange for Dana, a deal which Vigo accepts.
The Ghostbusters' investigation leads them to illegally excavate First Avenue at the point where the baby carriage stopped. Lowered underneath, Ray discovers a vast river of pink slime filling an abandoned pneumatic transit line. Attacked by the slime after obtaining a sample, Ray causes a city-wide blackout by accidentally kicking a cast iron pipe that breaks, falls, and shorts out an electric cable. After this, the Ghostbusters are arrested by the NYPD. Ineffectually defended by Louis Tully, they are found guilty of violating the restraining order by Judge Wexler, aka "The Hammer." Before they are taken to Riker's Island, Wexler angrily berates them. In response, the slime recovered by Ray and taken as evidence explodes, releasing the ghosts of two murderers that the judge had condemned to death that proceed to devastate the courtroom. The Ghostbusters capture the ghosts in return for the cancellation of the restraining order.
Later, the slime invades Dana's apartment via the bathtub and attacks her and Oscar. She seeks refuge with Peter, and the two begin to renew their relationship. Investigating the 'psychomagnatheric' slime and Vigo's history, the Ghostbusters discover that it reacts to emotions; it can be charged positively or negatively. They suspect that it has been generated by the negative attitudes of New Yorkers. While Peter and Dana have dinner together, Egon, Ray, and Winston explore the underground river of slime. While measuring its depth, Winston gets pulled into the slime flow, and Ray and Egon jump in after him. After they escape back to the surface Ray and Winston begin an angry argument, but Egon realizes that they are being influenced by the slime, so they strip off their clothes. They also learn the river is flowing underground directly to the museum where Dana works.
The Ghostbusters go to the mayor with their suspicions, but are dismissed; the mayor's assistant, Jack Hardemeyer, has them committed to a psychiatric hospital to protect the mayor's campaign for governor. Meanwhile, a spirit resembling Janosz as a nanny kidnaps Oscar from Peter's apartment, and Dana pursues them to the museum alone. After she enters, the museum is covered with a cocoon of impenetrable slime.
New Year's Eve sees a sudden increase of supernatural activity as the slime rises from the subway line and onto the city streets, causing widespread paranormal activity with ghosts attacking citizens. In response, the mayor fires Hardemeyer and has the Ghostbusters released. After heading to the museum, they are unable to breach the slime barrier with their proton packs. Determining that they need a powerful symbol to rally the citizens and weaken the slime, the Ghostbusters use positively charged mood slime and a remix of "Higher and Higher" to animate the Statue of Liberty and pilot it through the streets before the cheering crowds. As they arrive at the museum, the slime begins to recede and they use the Statue's flaming torch to break through a skylight to attack Vigo and Janosz.
Janosz is neutralized with positively charged mood slime, but Vigo immobilizes the Ghostbusters and attempts to transfer into Oscar's body. The positive feelings accompanying a chorus of "Auld Lang Syne" by the citizens outside weakens Vigo, returning him to the painting and freeing the Ghostbusters. Vigo momentarily possesses Ray, and the other Ghostbusters attack him with a combination of proton streams and positively charged mood slime. This destroys Vigo and changes the painting to a likeness of the four Ghostbusters standing protectively around Oscar. Outside, the Ghostbusters receive a standing ovation from the crowd and, at a later ceremony to restore the Statue, the Key to the City from the mayor.
Output: What do the Ghostbusters find out the slime reacts to?