- Billy (brown fish)
- Norma Rechid
- Eugene H. Krabs
- Squidward Tentacles (cameo)
- SpongeBob SquarePants
- Sheldon J. Plankton
- Karen Plankton
- Cave dwellers (debut)
- Abigail Marge
- Susie (first name revealed)
- Dennis (citizen)
- Frank (red shirt)
- Frankie Billy
- Fred (normal; blue)
- Harold (red fish)
- Nancy Suzy Fish
- Nat Peterson
- Nathiel Waters
- Taylor Fishbowl
- Tina Fran
- Frank (lifeguard)
- Harold Bill Reginald Scott
- Ivy (gray)
- Jimmy Gus
- Shelly Fishbowl
- Patrick Star
- Other Chum Caverns customers
- Sea turtles (mentioned)
- French Narrator
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 is not hungry, but Mr. Krabs handcuffs the fish to the ordering boat. Mr. Krabs then goes into the kitchen, where SpongeBob is flipping Krabby 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 is beautiful and Karen comes up with plan on how he could get more customers: he could lure them underground by the gorgeous scenery of the cave. In obvious fashion of Plankton, he ignores Karen before stealing her idea, to her annoyance. At that moment, Cave Dwellers appear but Plankton tames with his whip, making them his new employees.
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, where they lament their pointless feud has trapped them. The pair decide to work together if they ever get out, soon SpongeBob comes to save them.
When he does, Plankton goes back on his word to travel above ground again to steal the secret formula, but when he gets above ground, his act has caused a chain reaction that causes him to fals back down and so does the Krusty Krab and the Bikini Bottomites in the caverns to get trapped. Mr. Krabs berates Plankton for his foolish acts and 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 notes without Squidward, he needs somebody to take his place and looks up to Plankton. The episode ends by showing the cave dwellers forcing Plankton as cashiers while using whip to ensure he does the job.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
• SpongeBob Theme II - Nicolas Carr, Sage Guyton, Jeremy Wakefield [title card]
• Jovial Pirate's Jig - Michael Bolger, Nicolas Carr ["Looky, another bright-eyed, bushy-tailed customer!"]
‣ Vibe Q Sting - Nicolas Carr [secret formula hidden under Krabs' floor]
‣ Zelle 501 - Gerhard Trede [Plankton spying Krabs]
‣ Zelle 503 - Gerhard Trede [Plankton drilling underground]
‣ Big Bad Giant - Paddy Kingsland [drill hits a rock]
‣ Munitions Train - Harry Bluestone, Emil Cadkin [Plankton tunneling under the rock]
‣ Prologue of a Drama #9 - Delle Haensch, Hans Conzelmann [they fall into an underground cave]
• Steel Licks 7 - Jeremy Wakefield [they fall into an underground cave]
‣ Voyage of a Lifetime 1 - John Fox [pan of cave]
• Noodly Shenanigans - Nicolas Carr, Barry Anthony [Karen gets an idea]
‣ Harp Ding - Nicolas Carr ["Karen!"]
• Noodly Shenanigans - Nicolas Carr, Barry Anthony [Plankton thinks Karen's idea]
‣ Horror House of Wax Retro 2 - Nicolas Carr, Ron Wasserman [cave dwellers]
‣ Cellar Search - Philippe Pares ["From now on, you shall be my minions."]
‣ Tiki Rapido - Lionel Wendling [cave turned into a restaurant]
‣ Kommissar X - Gerhard Trede [cash register full of money]
• Steel Licks 20 - Jeremy Wakefield ["I'm running out of space for this stuff."]
• Tentically Speaking - Sage Guyton, Jeremy Wakefield [Patrick eating chum]
‣ Symphonic Panorama - Gregor F. Narholz ["You come down here to admire the subterranean splendor of the chum caverns."]
‣ Tiki Rapido - Lionel Wendling [gift shop]
• Steel Licks 8 - Jeremy Wakefield [SpongeBob goes back to the Krusty Krab]
• In a Minor Mood Jig - Michael Bolger, Nicolas Carr ["Where have you been?"]
‣ Battle March Link (f) - Keith Mansfield ["Krabs? What are you doing here?"]
• Salty Krab Jig - Michael Bolger, Nicolas Carr [SpongeBob selling Krabby Patties]
‣ Enter the Villain - Christopher Payne, Paul Rogers ["Krabs, you can't just slither down here and steal all my customers!"]
• What's This - Nicolas Carr ["Sea turtles, he called it!"]
• Slide Whistle Stooges - Nicolas Carr, Sage Guyton, Jeremy Wakefield [Plankton and Krabs tunneling under each other]
‣ The Great White - Gregor F. Narholz [Plankton and Krabs trapped underground]
‣ ? [Krabs yells that there's not way out]
‣ The Pollywog Strut - Nicolas Carr, Barry Anthony [Plankton tries to escape]
‣ Epic Tragedy - Gerhard Trede [Plankton and Mr. Krabs crying/Plankton and Mr. Krabs still crying 15 minutes later]
‣ Tearjerker [#79] - Harry Bluestone, Emil Cadkin ["Let's agree to work together."]
‣ Bridge H - Gregor Narholz ["Hang on a minute."]
‣ Film Fanfare (a) - Dick Stephen Walter [SpongeBob rescues them]
• What the Huh Vibe Sting - Nicolas Carr ["Where'd he go?"]
• Grass Skirt Chase - Sage Guyton, Jeremy Wakefield [Plankton trying to steal the formula]
‣ Sword Fight - Harry Bluestone, Emil Cadkin [everyone gets trapped underground]
‣ Pirate's Opus - Michael Bolger, Nicolas Carr ["Satisfied with yourself, Plankton?"]
‣ Nude Sting - Nicolas Carr [ending]
- The episode is available on the Viking-Sized Adventures, Season 6 Volume 2, Complete Sixth Season, The Best 200 Episodes Ever, Triple Pack 2, Big Hits: Volume 1, SpongeBob SquarePants Vol. 10 and Next 100 Episodes DVDs.
- Two clips from this episode were on the "Deep Sea Danger Zone" commercial, but it did not premiere during that week. It was planned to air as the fourth premiere, but was changed to "Squid's Visit."
- This is the last episode to air before Nickelodeon changed its logo into its current logo.
- This is the first episode where Bikini Bottom goes underground.
- There are two online games based on this episode called Gas Blast and Bubble Blast.
- In this episode, the secret formula is seen hidden 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. However, in most other episodes, it is seen in Mr. Krabs' safe.
- This is the second episode where people eat chum, thanks to the attraction. The first is "Chum Bucket Supreme."
- This is one of the few episodes where SpongeBob enjoys eating chum, as in the episode "Chum Bucket Supreme," he hates the taste of it.
- As of this episode, every main character has worn a Krusty Krab employee hat.
- This episode premiered on Lori Alan's 43rd birthday and three years after the Karate Island DVD was released.
- This episode marks the first mentioning of sea turtles in the series. They would later be shown in "Shell Games."
- During one part where Mr. Krabs and Plankton dig underground, it is 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 reference to the Morlocks 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 enter it from ground level. The second time, only six people enter at ground level.
- Plankton is on the surface at the end, but when the Krusty Krab falls underground, he is inside it.
- When Plankton first begins to dig, the drilling tool is on a wire. In the next scene, it is attached to the vehicle. His vehicle is destroyed when he reaches the Caverns. Then, later in the episode, it reappears when Plankton digs under Mr. Krabs.
- Mr. Krabs says there is a mandatory side of fries policy, but in earlier episodes, the customers mostly just get the Krabby Patty, or a Krabby Patty and a drink.