We begin 20-25 years after the events of the first GB in New York with Egon Spangler’s protegé, Holtzmann. She is a dedicated scientist working with Abby on studying paranormal phenomenon in Spangler’s labs in New York. Spangler retired and has not been seen since he left for an archaeological site overseas which had some relation to the Gozer incident.
Abby and Holtzmann are fired from the labs after their latest experiment brings about a ghost to speak to, but fails to re-establish the paranormal as an ongoing threat, and Holtzmann’s machine to measure PKE causes severe and costly damage to the lab’s equipment. Without jobs, Abby seeks out her friend, Erin, who is up for tenure. Erin refuses to help them because an association with them might cost her her tenure. Abby brings up that they were on the verge of breakthrough that might get Erin the acknowledgement she’s been seeking since her branding as Ghost Girl. Erin gets them to leave by promising that if they can bring empirical data, she will help, but not join them.
Abby visits Ray’s Occult books, and Ray hands over some books and equipment that Spangler left with him that indicates another major phenomenon is about to hit and PKE is being stored up somewhere which is causing an explosive buildup. Abby and Holtzmann follow a lead that allows them to trap a ghost, but barely.
With some empirical measurements in hand, Abby and Holtzmann return to Erin. Erin tells her skeptical boss to shove it, and joins Abby and Holtzmann, but without funding, they can’t get off the ground. Abby sells her stock and mortgages her home to get them into business. They hire the dumb receptionist, Erin crushes on him, and they all make fun of her for loving an idiot, but at least he works cheap. They are called in to a real emergency when the first of one major ghost trap fails and releases a ghost in a populated area, where Janine works. Using Egon’s notes, Holtzmann and Abby make some new ghost-catching equipment. They’re never sure whether Holtzmann’s stuff will work or kill them, but they manage to capture the ghost and the renewed interest in the Ghostbusters gets them on TV, etc. There is some concern as to whether these new Ghostbusters have what it takes, but it is not aimed at them being women.
At the site of the first ghost they trapped, an old Ghostbusters trap is found (or a replica) and is returned to Venkman, who returns it to the girls in a brief scene where he says he never wanted to be involved anyway; maybe he does his typical scam-artist bit and hits on the girls and they all think it’s gross. It seems that someone had contained the ghost, but it had broken free. They investigate the site and run into Rowan trying to recover the trap, and dismiss him as an awkward janitor.
The Ghostbusters continue to have trouble as suddenly the PKE booms again, for reasons they can’t figure out. They have great monetary and popular success, and hire on Patty at her insistence after interacting with her in the subway, where she discovers another one of the traps, and identifies Rowan. Rowan is following his plan from the movie, only rather than breaking ghosts out, he had been hiding traps at the locations in order to open them all at once, which he has now done. Rowan frames the Ghostbusters, having used the traps they sent, by talking to the Dean at MIT and convincing him of their complicity in trying to create their own success by freeing the ghosts. The Ghostbusters are arrested.
While in jail, the Ghostbusters discover the ley line problem by cross-referencing books that Dana Barrett sneaks into their cell; not being a ghostbuster and thus not suspicious, Dana had been convinced by Ray to get them the books. Meanwhile, Rowan commits suicide to open the final portal, bringing a building to collapse. National Guard and police armed with ghost-busting equipment provided by the old franchise have been unable to make a dent in the swirling vortex. Winston arrives, having taken a job at the mayor’s office and having just heard about them, and brings the girls before the mayor. The old franchise is all in the room, but Ray, Venkman, and Winston all agree that the new franchise has all the proper equipment and ability and should be the ones to handle it. Dana Barrett, however, decides to join them.
The new Ghostbusters, plus Dana, suit up and go to stop Rowan. Insecurities about Holtzmann’s equipment force Erin and Abby to fight about who is in charge, but Patty’s knowledge of the history of the building means that there are structural elements that they can take advantage of, to disable the portal. While fighting ghosts to set Holtzmann’s mega traps around the portal, they have several moments of needing to rely upon each other, as the traps continue to burst open from the extent of the activity. Eventually, it is determined that the containment field on the Ecto-1 needs to be dropped into the portal in order to stop it, so someone has to drive it in. Abby agrees to do it, since she feels guilty about having messed up Erin’s life, but while they are talking it over, Holtzmann remote-rigs the car to drive itself in.
When the portal explodes, it flows into Rowan’s corpse who becomes the big bad at the end. In order to stop the massive ghost, they have to cross the streams, which results in total protonic reversal. Holtzmann’s theory is that since the original franchise didn’t die, neither will they.
Ending possibility 1 (sci-fi bummer?):
Erin’s pack shorts and she dies, becomes a real “ghost girl” and helps from the other side. Thus the Ghostbusters have a ghost partner from then on.
Ending possibility 2 (homage bummer, but my favorite):
Erin’s pack shorts, but we see Egon on “the other side,” holding the pack together. He smiles, and disappears into the void as everything returns to normal.
Ending possibility 3:
Erin’s pack shorts, Abby leaps in to help her. There is a mighty explosion and the earth swallows them. Dana, Patty, and Holtzmann look about ready to give up, when Abby and Erin climb up out of the earth, having been saved from the fall by Holtzmann’s megatrap not quite completely consuming a marshmallowy creature of mammoth proportions.