Peter Venkman(Bill Murray), Ray Stantz(Dan Aykroyd), and Egon Spengler(Harold Ramis) are three scientists at Columbia University in New York City. When their grant expires, the guys are fired and they go into business as a ghost extermination company called "Ghostbusters". Their first customer is orchestra cello player Dana Barret(Sigourney Weaver)t, who was scared out of her apartment on the 22nd floor of a high rise apartment building on Central Park West. It seems that Dana's neighbor, Louis Tully(Rick Moranis), is also being affected by the strange happenings in the apartment building. Armed with proton guns, the Ghostbusters become wildly popular, and they are joined by Winston Zeddmore(Ernie Hudson), who is looking for a job with good pay. Overzealous Environmental Protection Agency (EPA) agent Walter Peck(William Atherton) thinks the Ghostbusters are frauds, and he has the Ghostbusters put in jail. Peck is forced to believe the Ghostbusters when New York City is put under siege by an ancient Sumerian God named Gozer the Gozerian, who is channeled through the apartment building that Dana and Louis live in, and the mayor has no choice but to let the Ghostbusters out of jail to face Gozer.
