The Ghostbusters mark the supernatural incidents on a New York map and realise they form ley lines, intersecting at the hotel where creepy Rowan works.
At the hotel they find his lair, where he has a machine he plans to use to release all ghosts and cause an apocalypse. They try to persuade him to stop, but at the last second he electrocutes himself in the machine. At first it appears the crisis is over as he is dead, but then they realise he is coming back as a powerful ghost to lead the other ghosts into the apocalypse.
Rowan possesses Melissa McCarthy, and then Chris Hemsworth, and opens the portal to the afterlife. Ghosts flood out and start destroying New York, including Slimer, who steals the Ghostbusters' car. Rowan takes the form of a huge ghost from the Ghostbusters logo.
The Ghostbusters realise they can only close the portal by making their car fall into it, carrying the nuclear pack it contains. The portal begins to shut, sucking in all the ghosts; at the last moment the huge Ghost grabs Melissa McCarthy and is sucked in with her. Kristen Wiig loops a cable round herself and dives into the portal, firing her proton stream at the huge Ghost, forcing him to let Melissa McCarthy go and grabs her. The other Ghostbusters reel the pair back in to safety.
The film ends with the Ghostbusters back in their office, watching a panorama of skyscrapers at night displaying 'we love GB' in neon lights.
Trivia: The "Demonic Balloons" that attack the Ghostbusters are almost direct re-creations of real Macy's Thanksgiving Day Parade balloons from the 1930's. The filmmakers decided to use the real designs in order to represent the "spirits" of New York's history... and also because they were quite eerie and unsettling.