Plot
Three years following the Summerville incident, Callie Spengler, her boyfriend Gary Grooberson, her children Trevor and Phoebe and their friends Lucky Domingo and Podcast, relocate to New York City to aid Winston Zeddemore and Ray Stantz in re-establishing the Ghostbusters. Following the team's most-recent ghost capture, Walter Peck, the Ghostbusters' long-time opponent and current mayor, threatens to put them out of business for good. To appease him, Callie removes Phoebe from the team for being underage. Upset, Phoebe plays chess in a nearby park, where she encounters and befriends Melody, a ghost of a teenager killed in a fire.
Ray and Podcast collect cursed objects for examination. Nadeem Razmaadi sells them a strange brass orb with ritual markings written in Mesopotamian Arabic. Knowing that copper-based alloys have long been believed to be spiritually conductive, Ray concludes that the orb is an apotropaic trap meant to contain a powerful entity. When Ray evaluates the orb's psychokinetic energy levels, it emits a broad-spectrum psionic burst. A cold wave travels from the orb to the Ghostbusters' firehouse headquarters and damages the containment unit, which is almost at full capacity.
Winston takes the orb to his company's paranormal research and development center, run by Doctor Lars Pinfield. Using an experimental device, he is unable to extract any orenda from it. The orb's captive psychically sabotages one of the center's confinements, allowing a "Possessor" ghost to escape and hide in Podcast's equipment. To learn more, Lars joins Trevor and Lucky to see Nadeem, who reveals that his grandmother kept the orb hidden within a brass-lined chamber. Peter Venkman, brought in to help, discovers Nadeem has latent pyrokinesis.
Ray takes Phoebe and Podcast to visit Doctor Hubert Wartzki, a research librarian and anthropologist at the New York Public Library, who explains that the orb was invented over four thousand years ago in West Asia by sorcerers known as the Firemasters. It was intended to imprison Garraka, a demigod who sought to conquer humanity by inflicting fear powerful enough to freeze living creatures to death. Garraka's vulnerability to fire and brass, coupled with the removal of his horns, allowed the Firemasters to trap him within the orb. Nadeem's grandmother was of the Firemasters' lineage and prevented Garraka from escaping in 1904 after he murdered the members of the Manhattan Adventurers' Society, who were conducting a mock ritual to free him.
When the trio attempts to stop the escaped Possessor from stealing a phonographic recording of the society's ritual, Peck exploits Phoebe's involvement to condemn the Ghostbusters' headquarters and confiscate their equipment. After an argument with Gary and her mother, Phoebe runs away and takes Melody to Winston's research center, where she uses his extraction equipment to project herself as a ghost for two minutes so she can physically interact with Melody. However, Melody reveals she has been secretly collaborating with Garraka, who has offered her passage to the afterlife. By controlling Phoebe's disembodied spirit, Garraka forces her physical body to recite the ritual chant. He then escapes, recovers his removed horns at Nadeem's residence and begins terrorizing the city. Knowing Garraka will liberate the ghosts in the containment unit after freeing the ones at the center, the Ghostbusters gather to defend their headquarters. They are aided by Nadeem, who dons the brass Firemaster armor kept by his grandmother and attempts to master his powers.
Garraka overpowers them and breaches the containment unit, but Phoebe confronts him and electroplates her proton pack with brass to strengthen it; Melody atones for her misdeeds by helping Nadeem utilize his powers to weaken Garraka. Ray, with help from his fellow veteran Ghostbusters including Janine Melnitz, reconfigures the containment unit to serve as a greater ghost trap and defeat Garraka. A passage is opened for Melody and she reconciles with Phoebe before departing for the afterlife to reunite with her family. With the city saved, the Ghostbusters are hailed as heroes again, with Peck forced to support the team and reinstate Phoebe, before pursuing the liberated ghosts, including Slimer and the Mini-Pufts.
