The Middleton Cheer Squad is in a schoolbus being driven to a cheer competition by Mr. Barkin, but Ron's Mad Dog antics are starting to eat away at certain members of the squad, namely Bonnie. As Kim warns Ron to act 'normal' for a change, Ron begins to notice something familiar about the road they are on. In a sudden panic, Ron calls Wade on the Kimmunicator wanting a GPS lock on his position. Wade obliges and the data confirms Ron worst fears, they are near Camp Wannaweep.
Ron urges Mr. Barkin to drive fast and explains the camp is the site of his worst summer ever and that he would never come back. Suddenly the bus drives over some tire spikes, causing the bus to come to a halt outside the main gates to Camp Wannaweep. Barkin informs the team that the bus has two flats and that they need to call for help. As such the girls all pull out cellphones only to find there is no signal and even the Kimmunicator is not working. Barkin tells Ron to lead them to a phone in the camp. It then dawns in Ron that he is in charge for once, according he declares to the team only he knows how to survive the dangers of Camp Wannaweep. The team enters the camp only to discover the phone is out of order. Tara recalls that their situation is just like from horror films, innocent teens trapped in the woods getting picked off one by one. Kim is quick to dispel that idea and even Bonnie agrees that if it were a movie there would be more guys. Kim announces that they are stuck for the night and might as well make the best of it.
As the team sits around the campfire Ron tells them stories of his time at Camp Wannaweep. Barkin tells Ron to stop, when Ron notices a rustle in the bushes. As Ron goes to investigate, Kim tells him to relax and enjoy the campfire. As they leave the bushes a swamp creature appears briefly watching the team. Kim and Barkin soon leave in search of more firewood, citing they cannot stand to listen to another of Ron's stories. As Barkin and Kim wander into the forest the swamp creature follows them. Back at the campfire Ron tells the story of the lake at Camp Wannaweep. In the story Ron recalls how he did not want to go swim in the lake due to the fact it was green, it smelled and he had seen the fish glowing at night. Ron ended up trading his afternoon swim with a kid called Gil Moss and Ron taking Gil's spot in arts and crafts. Back in the forest as Kim and Barkin collect firewood, Kim hears a noise. Barkin dismisses this, saying Ron's stories must be getting to her. Suddenly a creature grabs Barkin's leg and pulls him into the bushes. Kim notices Barkin has vanished and calls out to him, but there is no response. As Kim returns to the campfire she asks the rest of the team if they have seen Barkin. Kim asks where Liz and Marcella have gone, when suddenly two scream are heard. As Kim and Ron rush to the site, they find no trace of the girls and only a strange footprint in the dirt. Ron decides they must move to his old stronghold Cabin 13. As Kim and Ron debate over who is in charge, Barkin is heard calling out from the forest. Kim and Ron race out to find Barkin covered in green slime, talking about a strange creature that oozed muck.
Suddenly, screams are heard from the rest of the team. Kim, Ron and Barkin run back to Cabin 13 to find it in ruins, the rest of the team pinned to the walls by green slime and the mysterious creature. The creature then revels itself to be Gil, although he now calls himself "Gill" with an extra-L. Gill then traps Kim in his slime and tells Ron he knows all about how great Ron's life is. Gill reveals that the lake was toxic and the reason for his mutation. Gill also tells the team that he jammed their cellphones and caused the bus to crash in order to get his revenge on Ron. As Gill advances on Ron escapes through a tunnel in the floor of the cabin, as this happens Barkin starts to mutate due to contact with Gill's slime. Ron's tunnel emerges into the arts and crafts building and he begins collecting supplies. Gill suddenly burst through the floor and begins shooting slime throughout the room. But once again Ron is able to escape.
Ron is then seen building a net from crafts lanyard material while Rufus fixes an outboard on a motorboat. Ron and Rufus then take off across the lake in the motorboat. Gill hears the engine start and heads off after Ron. Suddenly, the boats engine dies, and Ron complains it is out of gas. Gill then appears next to the boat, so Ron dives into the lake. As Gill and Ron fight in the water a rope slips on to Gill's leg. Ron grabs the rope and tells Rufus to start the engine. The boat then hurtles across the lake will Gill in tow, until it crashes into the dock leaving Gill high and dry.
The next morning, Biohazard teams arrive to decontaminate the squad. Kim introduces Ron to Dr. Lurkin, who they hope will be able to reverse Gill's mutation. As Gill is taken away in a giant fish bowl, he once again vows revenge on Ron. As the squad leave the camp, they all thank Ron, and Tara even kisses him on the cheek. As Ron takes one last look at the camp, Kim comes over and congratulates him for saving everyone. As they leave, Ron asks if he can call the shots on their next mission, but Kim says that was "ferociously unlikely".
- This is the eleventh episode in chronological order.
- According to some lists, this is possibly the eighth in chronological order.
- This episode contained many elements of the summer camp horror genre. These include the setup of teens stranded at a summer camp; the "don't go off alone" rule so the characters need to use the buddy system; the characters disappearing singularly or in pairs; the the monster which remains hidden for the first part of the show; and the "something's wrong here" feeling caused by the unseen monster because Gill is unseen and everybody is freaked out.
- This was the first episode of Kim Possible ever to be offered on DisneyChannel.com.
- This episode also mentions that Ron shared a cabin with a "tick-infested chimp," but it does not show Bozo the Chimpanzee, or explain that Ron is terrified of monkeys in any way because of this incident.
- This episode also does not give any reason for Ron's pathological fear of small bugs and spiders, which it did give a flashback of in "Tick-Tick-Tick".
- The scene where Gil and Ron talks about Science Camp, Band Camp and Clown Camp would be used as a running gag again in the episode 'Return to Wannaweep', where Ron explained to campers that wanted to go at Band Camp where the camp actually was.
- The scene in which Kim and Mr. Barkin walk by the camera followed by Gill after they pass off screen is exactly the same sort of shot used in nearly every episode of Scooby-Doo, Where Are You! The lighting of the scene and overall design of Gill even make the scene appear like the classic TV show.
- Tara's description of "one of those horror movies" matches that of the original Friday the 13th movie.
- Although Ron is shown as the cheer squad mascot in this episode, he does not become the "Middleton Mad Dog" until "Attack of the Killer Bebes", which was produced prior to "Sink or Swim" but is set chronologically earlier.
- Ron's pockets frequently change from cargo pants pockets to normal pockets throughout this episode.
- Right after Ron says, "And it's back there!", the "13" on Cabin 13 is missing, then it appears again.
- The positions of the cheerleaders change over and over when they are being held captive by Gill.
- Right before he paused in a conversation with Kim after saying "Are kidding me? I-", Ron has two eyebrows above his left eye.
- When Ron said he was able to survive every evil Camp Wannaweep could throw at him, he did not survive the camp's mascot, Bobo the Chimpanzee, and all the bugs that crawled around in his cabin once. He does not even mention them.
- Kim Possible: The Complete 1st Season