Five years after saving New York City from a supernatural threat, the team of eccentric parapsychologists has disbanded, their ghost-busting business defunct following a slew of lawsuits and court orders. As a result, they've taken up various unfulfilling jobs: Ray owns a bookstore and performs at children's parties with Winston, Egon conducts experiments on human emotions, and Peter hosts a low-rated television show on psychic phenomena. Meanwhile, Dana Barrett, the former client and Peter's love interest, is trying to move on with her life and her new baby, Oscar. However, her tranquility is shattered when Oscar's carriage is mysteriously moved through the city streets by an unseen force, prompting her to seek the team’s help once more.

Investigation leads the team to discover a massive river of slime flowing beneath the city, reacting to the negative emotions of the inhabitants of New York. The slime's supernatural properties raise concern about its potential danger. Concurrently, Dana's colleague at the museum, Dr. Janosz Poha, becomes possessed by the spirit of Vigo the Carpathian, a 16th-century tyrant and sorcerer trapped in a painting, who plans to use the slime to return to life and conquer the modern world. The team must navigate the legal restrictions imposed on them, the public's skepticism, and their personal struggles to understand and confront the growing paranormal activity, while the increasing malevolence of the slime signals a looming crisis for the city.