- French Narrator
- Eugene H. Krabs
- SpongeBob SquarePants (2 cameos)
- Squidward Tentacles
- Sheldon J. Plankton
- Plankton's robot (debut)
- Karen Plankton
- Bar customers
- Plankton's imaginary family (debut)
- Plankton's cousins (debut)
Mr. Krabs announces to his employees that it is the 25th anniversary of the first time that Plankton attempted to steal his secret formula. A robot suddenly enters the restaurant and orders chili coral bits. After Mr. Krabs takes the robot's money, Plankton jumps out of it and demands the formula, only for Mr. Krabs to flush him down the toilet.
Plankton miserably returns to the Chum Bucket and Karen suggests hiring some henchmen to help him. After trying and failing to recruit some thugs at a nightclub, Plankton remembers that he has thousands of relatives across the sea and invites them all over to the Chum Bucket, imagining them to be evil geniuses like he is. However, when they arrive, he sees that they are all dim-witted hillbillies, and realizes that he's "been away from home longer than [he] 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.
Just as the Krusty Krab is about to close, Plankton and his relatives show up and burst in. They trap Mr. Krabs in a toilet and open the safe containing the Krabby Patty secret formula. Plankton pulls it out of the safe and 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
A horrified Plankton runs away from the Krusty Krab screaming with all his relatives. Mr. Krabs tells his employees that the formula Plankton read is just a fake and that Plankton will most likely figure this out and come back for the real one. He says that the real formula is hidden somewhere where nobody, not even Plankton, will be able to find it. Squidward then guesses that it is at Mr. Krabs' house under his mattress, and Mr. Krabs runs home yelling "Curse you, Squidward!"
- 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.
The "OUT" Storyboards
|( ‣ ) 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]
• Washboard 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, Part 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.
- This episode was originally titled "Plankton's Last Stand."
- When this episode first premiered with "Missing Identity," it aired before the latter episode due to its large advertising campaign. In subsequent reruns and production order, the order of the episode segments is reversed.
- Nickelodeon advertised this episode as "Plankton's Revenge."
- 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.
- 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 turns him into a cockroach; Mr. Krabs steps on him.
- Protesting to Mr. Krabs that he is not a cockroach on a picket sign; Mr. Krabs steps on him again.
- 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. Plankton also establishes this fact in "Spongicus."
- According to the phone book:
- There are five "S. Plankton"s.
- At maximum, there is one "M. Plankton."
- There are fifteen "N. Plankton"s.
- There are fifteen "O. Plankton"s and "P. Plankton"s each.
- There are at least four "W. Plankton"s.
- 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.
- This is Karen's first major role.
- Plankton's dialogue when he goes to the pool hall and speaks to the thugs was used in "Krusty Krab Training Video," only sped-up.
- 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."
- In early airings, the episode had an incorrect copyright date of 2001 in the credits. Later airings (and the original print of this episode) have the correct date of 2002.
- 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.
- 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."
- When Plankton screams and runs back to the Chum Bucket, the road is long and wavy and the restaurant is far away, when it should be straight across the street from the Krusty Krab.