After being fired from the university where they worked, three fringe researchers decide to open a paranormal investigation company in New York. Joined by a fourth member, they soon become the reference for the eradication of the specters that multiply. As they get into trouble with a lawyer who wants them shut down and all the captured creatures are released into the city, causing panic, the ghost hunters must join forces to face their greatest adversary, Gozer, a fearsome Sumerian god who has taken up residence in a building near Central Park in the company of his minions, the gatekeeper and the master of the keys.