The film begins at the New York Public Library, where librarian Alice Drummond is diligently organizing books in a quiet, secluded area. Unknown to her, books are mysteriously levitating nearby. As she passes the card catalog, it suddenly erupts, scattering its contents everywhere. Terrified, she attempts to escape but is petrified by an unseen ghost, setting the stage for an eerie adventure.
Following the title sequence, we transition to the Paranormal Studies Department at Columbia University, where Dr. Peter Venkman (Bill Murray) is testing ESP with a male student and a captivating female student (Jennifer Runyon). While Venkman toys with the experiment, he sneaks in flirtations, delighting in administering shocking tests to the male. When the male student storms off, Venkman shifts his attention entirely to the woman just as his colleague Dr. Ray Stantz (Dan Aykroyd) rushes in, urging Venkman to investigate the library's ghost sighting.
At the library, Venkman and Stantz join Dr. Egon Spengler (played by Harold Ramis) as they dive into the ghostly encounter. Here, they collect ectoplasmic residue and come across a towering stack of legendarily organized books, but soon, a ghostly figure—a translucent elderly lady (Ruth Oliver)—appears before them. Panicking, the men flee after the ghost morphs into a sinister, skeletal apparition, while the librarian looks on, confused.
Back at the university, despite their adrenaline-fueled excitement, the trio faces disillusionment when the dean (Jordan Charney) shuts down their funding due to dubious research findings. Determined, Venkman inspires Stantz to harness their abilities and start a new business specializing in paranormal investigations. After Venkman persuades Ray to mortgage his childhood home for initial capital, the duo is thrilled to move into an old firehouse as their new headquarters.
In a parallel storyline, we meet Dana Barrett (Sigourney Weaver), a classical musician who finds herself dealing with bizarre happenings in her apartment. Meanwhile, her neighbor, Louis Tully, is oblivious to her distress as he chats about hosting a party. Upon returning home, Dana is horrified to discover her eggs cooking themselves, and a horrifying specter named "Zuul" lurking in her fridge. In search of answers, Dana seeks help from the newly formed Ghostbusters at their makeshift headquarters, where Venkman can't resist flirting while investigating her case.
After an exhilarating first ghost capture at the Sedgwick Hotel, the Ghostbusters experience a surge of business as they gain notoriety. The film showcases an amusing montage of their escapades, including media appearances. As the plot thickens, Venkman finds himself entangled with Dana once again, only to learn that she's being targeted by an ancient Sumerian evil.
Meanwhile, they recruit Winston Zeddemore (Ernie Hudson), a blue-collar worker seeking a job, even as an EPA official, Walter Peck, begins to express concern over the Ghostbusters' methods. As supernatural chaos erupts across New York City, culminating in Dana being possessed, the Ghostbusters realize they must confront the formidable Gozer.
Their efforts crescendo atop Dana's building, where, amidst a battle against the supernatural, they must face the shocking and whimsical threat of the Stay Puft Marshmallow Man. As the streets tremble under his weight, they devise a plan to cross their streams, risking their lives to seal the portal Gozer has opened.
Triumphing over adversity, the Ghostbusters emerge, albeit covered in marshmallow, as they rescue Louis and Dana from their ghostly transformations. The film culminates in a jubilant celebration on the streets, encapsulating their victory with the cheers of the public, reaffirming their newfound status as heroes of the city. In the aftermath, Peter shares a romantic moment with Dana, proving that love, much like the supernatural, can be unpredictable yet wonderfully chaotic.
