The episode opens with Lee Ping and Camillio Martinez running through a laboratory setting pushing a unconscious Principal General Barrage on a wheel-chair. A handful of their classmates are with them, and a computer is reading a countdown for a self-destruct sequence.
It all started earlier that day, when Lee met with Holger Holgaart and Camillio on the bus, in a good mood because he got his bag back. Holger and Camillio are discusing the upcoming frog dissections. Camillio is excited, but Holger doesn't want to cut up the frogs. Lee also doesn't want to disect frogs because he finds the process gross.
While exiting the bus, Lee accidentally hits Camillio in the face with his bag, revealing something hard hidden in the lining. Camillio and Lee work together to find out what it is, but can only decipher that it's some sort of unidentified device. Before they can glean any additional details, they spot students panicking in the halls. The reason? The frogs that were supposed to have been dissected have been released into the school.
Camillio points out that the event has a similarity to The Prank, as frogs were released during The Prank as well, leading them to conclude that whomever is behind this is connected to The Prank. The Cleaners quarantine the frogs to a large portion of the school, leaving several smaller places frog free. Barrage refuses to cancel classes and instead orders that Class will be in the frog-free environments.
When Vice Principal Victoria points out that they can't fit everyone inside the comparatively small areas, Barrage improvises and schedules an impromptu field trip to the recently reopened Green Apple Splat factory for the tenth graders. Once on the island factory, Sal, a factory worker and their guide for the day, gives a history lesson about the factory. In the year 1956, Doctor Leopold Webber was working on a experiment involving frogs and apples. A lab accident occurred, and the experiment blew up in his face. However, he noticed that the resulting concoction tasted good, and as a result, Green Apple Splat was created.
It is also explained that the factory had to shut down production for 20 years because the nuclear generator used to power it went into meltdown and they've only recently reopened.
While Sal's back is turned, a trio of levers is pulled and the meltdown is triggered again. Lee suspects that the trio of Enviromentalists were responsible but everyone else believes it's yet another of Lee's pranks. Either way, an evacuation is ordered, in the process a portion of the class is left behind. This group consists of Lee, Camillio, Holger, Brandy Silver, Tina Kwee, the Mathletes, the Environmentalists, and Lynch Webber.
When she realizes that they've been left behind, Brandy convinces the class to help her find a way off the island. Meanwhile, Barrage realizes that some of the students were left behind and goes in after them. However, when the group sees Barrage's shadow, they jump to conclusions and assume that it's the ghost of factory workers long passed. As a result, the panicked tenth graders enter the sewer and try to escape, but instead become trapped with what can be best described as Cyborg Tazelwurms.
Barrage jumps in after the group and is able to fend off the creatures before the fumes fry his prothetics and knock him unconcious. Lee takes the opportunity to make the Environmentalists confess that they're responsible for everything–the meltdown, the release of the frogs, and The Prank. The trio confess they did turn the frogs loose on the school, they did accidentally release them during the prank, and they did trigger the meltdown, all in a poorly thought-out attempt to free the frogs in the factory..
Lee soon discovers that the device planted in his bag is a key to the door leading out of the sewers and into another underground laboratory similar to the one at the school. By using a wheelchair, he is able to get Barrage to safety, but the group is ambushed by more Tazelwurms. Barrage reawakens and saves the class from the Tazelwurms, which allows them to follow the tunnel to the safety of the mainland.
With the factory destroyed and everyone safe, Barrage demands to know who is responsible for what has happened, prompting everyone to point to the Environmentalists. Once home from a hectic day, Lee points out that the Environmentalists were only responsible for the frogs, and not the entire prank. He also examines the key, wondering if the Red Tazelwurm planted it in his bag for some reason.