Now that everyone is aware there is an alien spaceship beneath Fort Jerome, it's time to figure out how to get rid of it and rescue their dad. The Goosebumps: The Vanishing season finale has the teens working with Ramona to concoct a plan. Each of them will take a dose of her serum and descend into the underground chamber where they'll have an hour before it wears off to get their dad and return. Sounds good, right? But then Ramona seemingly betrays them by closing the hatch on them, locking them down there despite saying she'd leave it open.
Injecting Anthony's pod isn't too difficult and once he's reunited with Devin, Cece, and their friends, the group works together to figure out how to get back out of the chamber. Recalling the twin's first night in town and the moment Trey blew up the transformer, they consult blueprints left behind to figure out how to cut the power from the inside.
Anthony's plan involves using canisters of the serum that were prepped to be injected into the ship. He'll use it on the ship again while Trey blows the power, overloading the system. Their plan works, but unbeknownst to everyone else, Anthony has an ulterior motive. While down there, they discover four pods containing Matty, Hannah, Nicole, and Sameer. Anthony couldn't bear leaving without them so he used the canisters on them, too. Luckily, all of the kids and Anthony make it back to the hatch door in the nick of time.
Jen, having figured out where Alex went when her signal gets cut off ("as if she's underground"), arrives just as everyone emerges from the hatch.
Back at the Brewers' house, the reconvened group does their best to get Matty and his friends acclimated to this new world since they've basically time-traveled 40 years. Anthony and Matty have a tender reunion scene in the basement. But their troubles aren't over just yet. There's still the alien ship to contend with beneath town.
Anthony and Jen argue about what to do next, especially considering the four "dead kids" should be reported to someone. Jen is a cop, after all. But Anthony convinces her not to because they'd probably take Matty away again for testing. Instead, he and Jen will confront Ramona again and learn how to handle the spaceship.
Meanwhile, the teens remain at the house together with Cece, Alex, Devin, CJ, Trey, and Frankie dividing up to show Nicole, Sameer, Matty, and Hannah around town.
The adults receive a shock when they arrive in Ramona's lab and see Dr. Avi sitting on an exam table. She snuck back underground and removed him from his pod. Far from being happy about this, Avi says he was wrong the entire time and Ramona needs to let him go. Then he vomits sludge and transforms into a monster. Jen and Anthony realize that if Avi transforms... that means their children are in danger.
And as expected, across town each of the teens must contend with Matty and his trio of friends each turning into a chittering creature. It seems to confirm that the aliens have been using that black goop to reproduce with the pods serving as incubation.
Anthony realizes that Dr. Avi was trying to say that they were wrong for trying to kill the aliens in the past. They need to free the ship instead of trying to destroy it. Together they open a larger hatch and the ship takes off into the sky. Anthony passes out in the blast and has a vision of him and Matty in the tunnel. Matty tells him it's okay. It's time to let him go. The aliens are taking him, his friends, all of the scientists, Dr. Avi, and even Ramona, with them. It's over now.
With all of the horror wrapped up, the kids gather again at the Brewer house to say their goodbyes and reveal their plans for the rest of the summer. Cece is heading back into the city for her debate team, she's decided she loves debate and doesn't want to let the stress of academia ruin it for her. She and Alex intend to try a long-distance relationship.
But Devin has found a home in Gravesend, so he'll be staying with his dad. He and Frankie appear to be official now and are still on good terms with Trey. CJ gets his job back at his parent's restaurant and finally gets that promotion.
Everyone seems happy.... until the final scene shows Trey alone, vomiting up more of that alien sludge. Does that mean he's about to turn into a monster, too? Did he get re-infected? And if he did, wouldn't the serum help him? Lots of possibilities!
All episodes of Goosebumps: The Vanishing are now streaming on Hulu and Disney+.