"The Rookie" was hired by the Ghostbusters as a fifth member in the year 1991, two years after the team defeated Vigo the Carpathian, and seven years after they prevented Gozer from conquering the Earth. By this point, the Ghostbusters are recognized as genuine heroes by the city of New York, and the mayor's office foots the bills for all of their jobs, which are now seen as a public service. The Rookie is brought on as the team's new Experimental Equipment Technician, which means he'll be testing Ray Stantz and Egon Spengler's dangerous new prototype ghostbusting equipment, ranging from simple upgrades like the Boson Dart blast for the standard proton stream to newer, more threatening designs like the Dark Matter Generator's Shock Blast and Stasis Beam abilities. In the opening cutscene, Ray asks the Rookie his name, but as he goes to answer, he is interrupted by Peter Venkman, who insists on not knowing his name, alluding to a previous Experimental Equipment Technician who apparently met an unfortunate fate.
Throughout the game, the Rookie rides along with the Ghostbusters, seemingly befriending the down to earth Winston Zeddemore the most, as they investigate the mystery of the massive pulse of psi energy released from the Gozer exhibit at New York's Natural History Museum, and the sudden, incredible spike in ghost activity that it brings with it. Along the way, he faces off against the spirits of Gozer cultists, the Librarian ghost who evaded the team's very first attempt to study the supernatural, and most notably, found himself singularly responsible for defeating a revived Stay-Puft Marshmallow Man, albeit in a much weaker form than his original appearance.
By the end of the game, when Ivo Shandor's ominous mandala has been destroyed, and Shandor's plan to become a Destructor god and reshape the world in his own image has been prevented, the Ghostbusters determine that with ghost activity in NYC calming down, the team no longer needs a fifth man. However, rather than just fire the Rookie, the team have decided to make the Rookie the leader of the very first Ghostbusters franchise office, which will soon be founded in Chicago, Cincinnati, or Los Angeles. Soon there'll be another team of Ghostbusters protecting the world of the living from supernatural threats, and the Rookie will be in command!