The episode starts with Mr. Krabs kicking out two customers saying they should listen to the sign about the mandatory side of fries policy. Another customer comes in and says he's not hungry, but Mr. Krabs handcuffs the fish to the ordering boat. Mr. Krabs then goes into the kitchen, where SpongeBob is flipping patties as usual and gives SpongeBob two spatulas so he can do twice the work. Mr. Krabs walks away going back to his office. In his office, Mr. Krabs trips on a loose floorboard. He uncovers it to reveal the Krabby Patty Secret Formula. Mr. Krabs takes a hammer and nails the floorboard back down.
The camera zooms out to show that Plankton is watching from his enormous telescope that goes out the Chum Bucket and into the Krusty Krab through the chimney. Plankton discovers that Mr. Krabs hides the Krabby Patty Secret Formula under the Krusty Krab floor boards, after Mr. Krabs trips over a lose nail, and goes to get it by caving in under ground, however he crashes into a big rock, and when he digs deeper to go around it, he gets trapped in an underground cave. Plankton discovers it's beautiful and comes up with plan on how he could get more customers: he'll lure them underground by the gorgeous scenery of the cave.
Later that day, Mr. Krabs discovers that Plankton has more customers by his cave and decides to go down there to sell Krabby Patties. Plankton is mad about this and decides to get his revenge by trapping Mr. Krabs underground. The two end up fighting, trying to get each other trapped underground. They end up both getting stuck underground and SpongeBob comes to save them.
When he does, Plankton goes above ground again to steal the secret formula, but when he gets above ground, he falls back down and so does the Krusty Krab and the Bikini Bottomites get trapped. Mr. Krabs complains they are all stuck together in one place. However, one customer approves that at least they are in a restaurant together. Mr. Krabs accepts it, but without Squidward, he needs somebody to take his place, and looks up to Plankton. The episode ends with the Cave Dwellers and Plankton as Cashiers.
I can turn into a skyscraper!
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This is the last episode before Nickelodeon changes it's old logo into it's current. (from an orange blob with white letters to lowercased orange letters that spell NICK).
This is the first time the Bikini Bottom went underground. The other time Bikini Bottom went underground was in "That Sinking Feeling."
In this episode, the secret formula is seen hid under a wooden plank floor in Mr. Krabs' office, but in the episode "Plankton's Army," Squidward says "Let me guess, it's at home, under your mattress," and Mr. Krabs rushes to his house. It is possible that he moved the secret formula to his office after Squidward revealed where he hid it.
This is the second time people eat chum, thanks to the attraction. The first was in "Chum Bucket Supreme."
This is one of few times SpongeBob enjoys eating chum as in the episode "Chum Bucket Supreme," he hates the taste of it.
This is the first and only time sea turtles have been mentioned or even referenced in the series.
In the Chum Caverns, there is no elevator shown going back up.
The first time the elevator is shown going down, eight people enter it from ground level. The second time, only six people enter at ground level.
Plankton was on the surface at the end, but when the Krusty Krab fell underground, he was inside the Krusty Krab.
When Plankton first begun to dig, the drilling tool was on a wire. In the next scene, it was attached to the vehicle. His vehicle was destroyed when he reached the Caverns. Then, later in the episode, it reappears when Plankton was digging under Mr. Krabs.