- French Narrator
- Eugene H. Krabs
- SpongeBob SquarePants
- Squidward Tentacles
- Sheldon J. Plankton
- Plankton's robot (debut)
- Karen Plankton
- Bar customers
- Plankton's imaginary family (debut)
- Plankton's cousins (debut)
In the beginning of the episode. Mr. Krabs announces to his employees that it is the 25th anniversary of the first time Plankton attempted to steal his secret recipe. A robot suddenly enters the restaurant and orders chili coral bits instead of a Krabby Patty. Mr. Krabs is suspicious, but takes the customer's money anyway. When the robot leaves, Plankton jumps out of the dollar bill and demands the formula, only for Mr. Krabs to flush him down the toilet.
Plankton returns to the Chum Bucket in misery, and Karen suggests hiring some henchmen to help him. After trying and failing to recruit some tough guys at a nightclub, Plankton then realizes that he has thousands of relatives across the sea and invites them all to come to the Chum Bucket, imagining them to all be evil geniuses like he is. However, when they arrive, he finds out they are all unsophisticated country bumpkins, and realizes that he's been away from home longer than thought."
After his cousin Clem reintroduces Plankton to all his relatives, Plankton calls them to a meeting and explains his plan, promising them all the root beer they can drink if they help.
Mr. Krabs is telling Squidward that it is almost closing time, with Plankton nowhere to be seen, thinking it's over. However, Plankton returns to the Krusty Krab and threatens them, as Mr. Krabs asks what army he has to back up threat and Plankton shows him the surrounded restaurant. Seeing this, Mr. Krabs believes that Plankton just planted Grass, until Plankton and his army laugh. Mr. Krabs and Squidward run, but Plankton and his army charge in a with a fierce attack, trapping them in a toilet. Plankton's cousins open the safe containing the Krabby Patty secret recipe and Plankton pulls it out. Mr. Krabs pleads with him not to read it, saying "There are some things in this world that aren't meant for mortal eyes." Plankton takes no notice and reads it anyway:
- A pinch of salt
- 3 teaspoons of chopped onions
- A cup of love
- 4 heaping pounds of freshly ground Plankton
Plankton is horrified and runs away from the Krusty Krab screaming with all his relatives, except for Clem who can't read. Squidward asks if that was the real Krabby Patty formula, Mr. Krabs explains it was just a fake and Plankton will most likely figure that out and be back to find out about the real formula.
He tells his employees that the real formula is hidden somewhere where nobody - not even Plankton - will be able to find it. Squidward then guesses that it's at Mr. Krabs' house under his mattress, and Mr. Krabs runs home yelling "Curse you, Squidward!" as the episode ends.
- Karen showing "SHELDON" on her screen as Plankton is trying to talk to his relatives.
- Someone running home after they learn something horrifying, and the road is much more curved and longer than usual.
- Mr. Krabs stepping on Plankton.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Zelle 506 - Gerhard Trede [Title card]
‣ Keel Row - Brian Peters [Opening]
‣ Premonition of Disaster - Arthur Harold Wilkinson [robot customer enters]
‣ Tomfoolery - David Snell [robot orders chili coral bits]
‣ Six Powerful Cues (A) - Wilfred William Burns [Plankton jumps out of dollar bill]
‣ Drunken Sailor (B) - Robin Jeffrey, Tim Laycock [Plankton flushed down toilet]
‣ Al Capone Blues - Eric Gemsa [Plankton goes home]
• Idea Vibe - Nicolas Carr ["Henchmen?"]
‣ Zelle 501 - Gerhard Trede ["I'll canvass all the seediest lowbrow dives in town to find my minions!"]
‣ Rocking Monster A - Wolfgang Killian, Hermann Langschwert [tough guys playing pool]
• Drowsy Reef - Sage Guyton, Jeremy Wakefield [Plankton in a wheelchair]
• Harp! - Nicolas Carr ["Wait... that's it!"]
‣ Jerry Cotton - Gerhard Trede [Plankton gathering family members]
‣ Let's Dance Susanna - Roy Henley [they're all hillbillies]
• Washboards and Spoons - Nicolas Carr [Overlays "Let's Dance Susanna"]
‣ Wooden Bear - Gil Flat, Tony Tape, Florian Voelxen [Plankton introduces them to Karen]
‣ Buffalo Girls - Martyn Laight ["What's in it for us?"]
‣ Zelle 503 - Gerhard Trede ["Root beer?!"]
‣ Zelle 506 - Gerhard Trede ["I have the restaurant surrounded."]
‣ Hog Fever (A) - Graham D.H. Preskett [plankton invade Krusty Krab]
‣ Kommissar X - Gerhard Trede [Krabs in toilet]
‣ The Oracle - David Farnon [safe opened]
‣ Journey to the Magic Island - Gregor F. Narholz [Plankton removes formula from bottle]
‣ Apalachian Banjo Duel - Larry Hochman ["And of course I had a little help from the family."]
‣ Dramatic Climax - Mike Sunderland [Krabs warns Plankton not to look at the formula]
• Snare Drum Please - Nicolas Carr ["Drumroll, please"]
‣ Against the Law (E) - Wilfred William Burns [Plankton reading the formula]
• SpongeBob Theme - Sage Guyton, Jeremy Wakefield [Plankton runs away]
‣ Let's Dance Susanna - Roy Henley ["Get outta here!"]
‣ The Tip Top Polka/The Cliff Polka - Chelmsford Folk Band [Krabs says it wasn't the real formula]
• SpongeBob Theme - Sage Guyton, Jeremy Wakefield [ending]
- This episode is available on the SpongeBob Goes Prehistoric, Absorbing Favorites, Complete 3rd Season, The Ultimate Box Set, First 100 Episodes, Exposed!: The Ultimate Box Set, SpongeBob's Legendary Adventures, The Ultimate SpongeBob Box Set, SpongeBob SquarePants Vol. 5, Complete Third Season, From the Beginning, Pt.2, The SpongeBob SquarePants Collection, Sheldon Plankton: Mean and Green, The SpongeBob SquarePants 8 Season DVD Collection, Favorite Episodes, Triple Pack 4, 2-Season TV Pack, The Third & Fourth Seasons, Big Hits: Volume 2, and The Best 200 Episodes Ever DVDs.
- "Plankton's Army" was ranked #66 during the Best Day Ever event from November 9–10, 2006.
- "Plankton's Army" was ranked #91 during the SpongeBob's Top 100 event in the UK and Ireland from June 4-8, 2012.
- The original name of the episode was "Plankton's Last Stand."
- This is the last episode to have Jay Lender, Sam Henderson, and Sean Dempsey's names seen in the opening credits.
- This episode features one of SpongeBob's smallest roles as he only appears in two scenes (one at the beginning and one at the end) and only speaks four lines.
- SpongeBob was originally going to be tied up while Squidward was going to be cut by a laser by Clem while Plankton reads the Secret Formula and Mr. Krabs is in the toilet, but Squidward was in the toilet with Mr. Krabs in the final cut.
- Plankton's past attempts at stealing the formula and results shown in this episode include:
- Asking nicely; Mr. Krabs says no.
- Wearing a cockroach costume; Mr. Krabs steps on him.
- Drinking a potion that turned him into a cockroach; Mr. Krabs steps on him.
- Protesting to Krabs that he is not a cockroach on a picket sign ("civil disobedience"); Krabs steps on him again.
- This episode is one of the rare occasions where Plankton is squashed by his wife, Karen.
- In this episode, Mr. Krabs claims that Plankton has been trying to steal the formula for 25 years; however, in "Spy Buddies," he claims that Plankton has been trying to steal it for 20 years.
- According to the phone book:
- There are five "S. Plankton"s.
- At maximum, there is one "M. Plankton."
- There are 15 "N. Plankton"s.
- There are 15 "O. Plankton"s and "P. Plankton"s each.
- The number Plankton dialed on the phone is 1934428.
- It is revealed that Plankton's full name is "Sheldon J. Plankton."
- Despite being married to him, Karen apparently did not know Plankton's first name until this episode.
- It turns out that Mr. Krabs hides the Krabby Patty secret formula in his mattress, which is also where he hides his money.
- When Plankton runs away from the Krusty Krab and back to the Chum Bucket, it is similar to SpongeBob screaming and running back to his house in "I'm with Stupid."
- The background of the title card is camouflage, the pattern of clothing worn by soldiers in the army.
- Plankton's robot looks similar to the Cylons from the 1978 TV show Battlestar Galactica.
- When Karen accidentally crushes Plankton, his limbs break and he attaches them back on in a similar fashion to Mr. Potato Head.
- The name of Plankton's cousin Billy Billy Bo-Illy Bonana Fanna Fo-Filly is a reference to the song "The Name Game."
- When Mr. Krabs says, "Today is the 25th anniversary of the first time my arch rival, Plankton, ever tried to steal me secret Krabby Patty formula," the door to his office is shown; but when the robot shows up, the door is gone, then when Mr. Krabs and Squidward walk outside, the door is back.
- When the robot shows up at the Krusty Krab, the Chum Bucket across the street is missing.
- When Plankton says, "Who will join me!", his mouth is out of sync.
- The phone book does not contain any phone numbers.
- When Plankton was licking the envelope, he should have been stuck to his saliva because that is how envelopes close.
- When SpongeBob arrives at Mr. Krabs' office, he doesn't have his hat on, but in the next shot, he has the hat on.
- When Plankton asks for the secret formula the second time, Mr. Krabs says "Uh-uh," but the captions say he says" Uh-huh," adding an extra "H."