NOTE: This spoiler was submitted by Jeremy

Summerville, Oklahoma – The Ecto-1 bursts out of a mine belonging to Shandor Mining, as Egon Spengler is being chased by an unseen spectral entity. He makes it back to his house and attempts to spring a huge ghost trap on it, but the trap fails when he cannot activate it. Egon runs back into the house and prepares himself, but the ghost gets Egon in his chair and kills him.

Egon’s estranged daughter Callie (Carrie Coon) lives with her kids Trevor (Finn Wolfhard) and Phoebe (Mckenna Grace), the latter sharing Egon’s keen interest in science. They are soon evicted from their home due to Callie being unable to come up with rent money, but she learns that Egon left her family the house in Summerville, so she packs up her things with the kids and heads out there.

The family makes it to Egon’s house, which everyone in town just knew as the home of the “dirt farmer” since he was such a recluse. The house is a dump, but Callie hopes they can make it their new home. They are met by Janine Melnitz (Annie Potts), who informs Callie that Egon left them saddled with a lot of debt, with Janine having been the one to take care of bills.

Callie later takes the kids to get dinner at a burger shop, where Trevor goes in to apply for a job. He is instantly smitten with an older girl named Lucky (Celeste O’Connor) who works there, but the other guys tease Trevor as he tries to talk to her. When they return home, Phoebe notices her chessboard and pieces all scattered on the ground, so she resets them before going to bed. Meanwhile, Trevor walks around outside and goes to the barn where he discovers the Ecto-1.

In the morning, Phoebe finds that one of the chess pieces moved, so she moves one of her own pieces. Callie drives Trevor to start work at the burger place while Phoebe starts summer school. She meets her teacher, Mr. Grooberson (Paul Rudd), and her classmate Podcast (Logan Kim), who has his own, er, podcast for the supernatural. Grooberson puts on “Cujo” for the class instead of teaching, and an earthquake happens. Phoebe goes to Grooberson’s office, where she learns that he is a seismologist and has been monitoring seismic activity coming from somewhere in town over the last few years.

Phoebe and Podcast later walk toward the mines where they find what looks like an old skeleton of a monster. Back home, Trevor starts to fix up the Ecto-1’s engine. Later at night, Phoebe sees that the chess pieces moved again, and when she moves her own piece, the ghost in the room knocks her piece off the board. She looks around the house some more and finds Egon’s PKE meter and an old ghost trap.

Back at school, Phoebe brings the ghost trap and shows Podcast, but Grooberson sees it and becomes curious. He tells Phoebe and Podcast that despite Summerville not having an epicenter, it has experienced a lot of earthquakes in recent years. He brings up the old ghost sightings and shows Phoebe and Podcast a video of the original Ghostbusters after they saved Manhattan from destruction in the 80’s, and Phoebe learns that her grandfather was a Ghostbuster. Grooberson takes them outside the school to see how the trap works, but they accidentally unleash a monstrous ghost that flies toward the Shandor mine.

Grooberson takes Phoebe and Podcast back home, where it appears there is some chemistry between Callie and Grooberson. The kids go through more of Egon’s stuff, finding a book about Gozer the Gozerian, the same evil ancient entity that terrorized Manhattan all those years ago, as well as the knowledge of Gozer being freed by the Gatekeeper and Keymaster. Meanwhile, Lucky invites Trevor to go out with her friends to hang out at the mines, where they find one of the ghostly entities bursts out and flies away.

Phoebe takes the PKE meter and goes to the barn where she comes across Egon’s old workspace and computer room. She finds his old uniform with his name on it, and soon realizes that the ghost that’s been following her IS Egon. She fixes up one of his devices before returning to her room. When Phoebe later asks Callie what kind of scientist Egon was, she brushes him off with resentment for abandoning her and her mother.

In the morning, Phoebe brings Egon’s old proton pack to show Podcast as they test out the beam, which turns out to still be powerful. They then hear a noise coming from inside a building, and they find a blue blobby ghost that they name Muncher (Josh Gad) because it eats metal. The ghost spots Phoebe and Podcast and attacks by roaring out metal shards at them. They fire the proton beam at Muncher, causing him to fly away. They chase after the ghost, just as Trevor rides in after having fixed up the Ecto-1 and taking it out for a spin. He picks up Phoebe and Podcast as they chase after Muncher, with Phoebe sitting in the car’s retractable seat and continuing to fire the proton beam at Muncher. Meanwhile, Callie is on a date with Grooberson, expressing her worries about Phoebe not fitting in. The kids drive through town chasing Muncher and firing the beam, which Callie and Grooberson notice. The three chase Muncher outside of town going toward the mine, using a remote-controlled trap to catch the ghost. As they are driving back, they are caught and arrested by Sheriff Domingo (Bokeem Woodbine).

In the jail cell, the three find that Lucky is Domingo’s daughter, but she backs up Trevor’s account of the ghost they saw as he tells Phoebe and Podcast. Phoebe uses her one phone call to contact Ray Stanz (Dan Aykroyd), who runs an occult antique shop out of the former Ghostbusters headquarters. When Phoebe mentions Egon, Ray says he can rot in Hell until Phoebe mentions he is dead, at which point he feels remorse. Ray explains to Phoebe that Egon had a major falling out with him and the other Ghostbusters before he retreated to Summerville with every single bit of their old equipment. The last time Ray spoke to Egon, he mentioned some crazy talk about the apocalypse. Phoebe manages to tell Ray she is Egon’s granddaughter before Domingo makes her hang up. Callie and Grooberson come to bail the kids out, but Domingo keeps all the Ghostbusters equipment in storage.

When they get home, Phoebe and Callie argue, as Phoebe has come to understand and respect what Egon did, but Callie still sees him as a bad father and doesn’t want her daughter mixed up in his business. Back at the mine, something awakens.

Grooberson goes to Wal-Mart for ice cream but then notices little bags of Stay-Puft marshmallows coming to life, with little marshmallow men popping out of the bags. Grooberson keeps walking until he finds Vinz Clortho (the Keymaster) in the aisle. He runs for his life, but the beast chases Grooberson all the way to his car and attacks him.

The next day, Phoebe and Podcast bring Trevor and Lucky to the mine to do more investigating. They find a temple with a statue of Gozer, plus the preserved body of Ivo Shandor (JK Simmons), a cult leader devoted to Gozer. There are years marked on the walls from various seismic events over the decades, and it looks as though Shandor was preparing to reawaken in the current year for Gozer’s return. Another earthquake happens, but the kids discover the source – a ghostly portal underneath a trap Egon built to keep Gozer and other evil ghosts at bay. The trap activates when Gozer tries to emerge, and the kids run.

Callie finds the PKE meter and comes across Egon’s lab and eventually realizes his ghost is there too. He has been keeping up with her growing up, with pictures and news articles of her all over his wall, meaning he really did love her. Unfortunately, she is found and attacked by Zuul (the Gatekeeper).

The kids return home to find Callie possessed by Zuul. She becomes feral and attacks them, while Grooberson, now possessed by Vinz Clortho, disables Egon’s trap, leading to many evil ghosts to be set free into Summerville. The kids go to Egon’s lab and get his equipment and uniforms to try and stop Gozer themselves. As the town falls into widespread panic, the kids go to the station where they free Muncher so he can eat through the metal bars and get the confiscated equipment. While this goes on, Zuul and Vinz Clortho gather to summon Gozer.

The new Ghostbusters drive toward the site of the chaos, as Zuul and Vinz Clortho bring forth the old temple and revive Gozer’s human form (Olivia Wilde). Shandor awakens and tries to appease the evil ghost, but Gozer tears Shandor in two pieces. The four arrive to fight back, with Podcast managing to weaken Zuul and break Callie free from her possession by trapping Zuul. Gozer is temporarily weakened, but the trap malfunctions and Zuul possess Lucky, allowing Gozer to regain power. It tries to kill Callie and the other kids, until someone calls out, “Hey, flat top!” Cue the ORIGINAL Ghostbusters – Ray, Peter Venkman (Bill Murray), and Winston Zeddemore (Ernie Hudson) – arriving to help out. They cross the streams to get Gozer, but the evil ghost overpowers them and breaks through. Phoebe attempts to get Gozer on her own, at which point Egon’s ghost materializes and helps her hold it right. He stands alongside his former friends and partners, and together with Trevor and Podcast, they manage to activate the trap to consume Gozer, Zuul, and Vinz Clortho.

Trevor helps break Lucky out of the shell that was once Zuul, along with Grooberson coming out of the Vinz Clortho shell. The old Ghostbusters talk to the new ones, and Venkman acknowledges that Phoebe really is Egon’s granddaughter. Egon’s ghost looks at his friends, as they reconcile for their earlier feud, and Callie is able to finally hug her father before he crosses over. The old Ghostbusters return to New York City in the Ecto-1, and we see the words “For Harold.”

Mid-Credits Scene: Venkman is seen married to Dana Barrett (Sigourney Weaver), who is doing his old electro-shock test on him.

Post-Credits Scene: A flashback is shown (a deleted scene from the original movie) of Egon giving Janine a coin. In the present day, she shows the coin to Winston, who is making arrangements to have the old headquarters and Ecto-1 restored. Meanwhile, one of the ghost containment units starts to glow red…

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More than 30 years after saving Manhattan from Gozer the Gozerian, Egon Spengler abandoned his former Ghostbuster friends and his own family because he knew the evil ghost would return. Egon is killed by one of Gozer's minions, and his estranged daughter Callie inherits his old farmhouse. She moves to Summerville, Oklahoma with her kids Trevor and Phoebe.

Phoebe befriends another kid called Podcast, and they come across the mines of Ivo Shandor, the cult leader who worshipped Gozer. With the help of their teacher Mr. Grooberson, they learn about the seismic activities that affected Summerville over the years, which has a connection to the mine where the ghost activity is coming from. Phoebe finds out that her grandfather was a Ghostbuster and finds his old equipment, including a trap that she accidentally opens with Podcast and Grooberson, unleashing one of Gozer's minions. Along with Trevor and his new friend Lucky, the four team up after Phoebe, Podcast, and Trevor catch a blue ghost called Muncher.

Gozer's minions Zuul and Vinz Clortho break free and possess Callie and Grooberson, allowing them to gather to summon Gozer. Shandor reawakens as he was kept preserved to prepare for Gozer's return, but Gozer kills him before preparing to face off against the young Ghostbusters. They break Callie free from Zuul's possession, but it just moves onto Lucky. Before Gozer can kill them, they are joined by the original Ghostbusters - Peter Venkman, Ray Stanz, and Winston Zeddemore - after Phoebe got in touch with Ray and told her she is Egon's granddaughter. The two teams join forces, along with Egon's ghost, to once again defeat and trap Gozer, Zuul, and Vinz Clortho. Egon's ghost reconciles with his friends and family before crossing over.