Kristen Wiig plays Erin Gilbert, an ambitious associate professor seeking tenure at New York's prestigious Columbia University who ends up losing that when a book she published years ago on ghosts surfaces, putting the credibility of the institution in question should she remain in the faculty. Turns out that her writing partner, Abby Yates, republished the book that had previously been out of print, and ends up cajoling Erin to just come help her and her current research partner, the kooky gearhead engineer Jillian Holtzmann, in her studies in investigating paranormal activity further, . They initially find success in trapping ghosts with Jillian's devices and their continued pursuit leads them to start a business and take on a fourth team member in Patty Tolan, a street-wise MTA subway employee who has seen a particularly nasty apparition in the subways of New York, and whose knowledge of the city will be of particular help, plus an daft-but-hunky administrative assistant in Kevin. But the ghostly activity seems to be on the rise, with signs pointing toward an oddball loner janitor named Rowan, who seems to be Hell-bent on bringing the generally unseen demons and ghouls to the Earthly plane that hasn't been so kind to regarding his genius.