Plankton discovers that Mr. Krabs hides the Krabby Patty secret Formula under the 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 its beautiful and comes up with plan on how he could get more customers, he'll lure them under ground 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 under ground. They end up both getting stuck under ground 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 Bottomies gets trapped, The episode ends with the Cave Dwellers and Plankton as Cashiers.
Home video releases
- SpongeBob SquarePants: Viking-Sized Adventures
- SpongeBob SquarePants: Season 6, Volume 2
- SpongeBob SquarePants: The Complete 6th Season
- Two clips from this episode were used in the Deep Sea Danger Zone commercial, but it did not premiere during the week. It was planned to air as the fourth premiere, but was changed to "Squid's Visit".
- With everyone trapped underground in the end of the episode, sooner or later they'll notice that they won't be able to pay for the Krabby Patties or run out, thus there won't be nothing left to eat.
- Another time Bikini Bottom went underground was in That Sinking Feeling.
- In this episode, the secret recipe 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 recipe to his office after Squidward revealed where he hid it.
- This is one of few times SpongeBob enjoys eating chum as in the episode Chum Bucket Supreme, he hates the taste of it.
- During one part where Mr. Krabs and Plankton are digging underground, it may be a reference to the classic Namco arcade game Dig Dug, when they keep going under each other to make the other one fall.
- The Cave Dwellers in this episode are a play on the Morlock's from the 1960 film The Time Machine
- In the Chum Caverns, there is no elevator shown going back up.
- The first time the elevator is shown going down, eight people are 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.