At the Krusty Krab, Mr. Krabs announces that it is the 25th anniversary of the first time Plankton attempted to steal his secret recipe. Suddenly, a robot enters the restaurant, and Mr. Krabs tells SpongeBob to clean out the men's bathroom and pushes Squidward aside, saying that he will handle this customer. However, the robot orders chili coral bits instead of a Krabby Patty, it pays for them and leaves. Mr. Krabs is surprised that the robot wasn't Plankton, but Plankton then suddenly jumps out of the dollar bill the robot gave him. However, Plankton hadn't planned what to do next, not thinking he'd get this far, and is simply flushed down the toilet by Mr. Krabs.
He returns to the Chum Bucket, sulking to his computer wife, Karen about his failures. She then suggests hiring some henchmen to help him. He first goes to the Salty Spittoon, but the thugs beat him up. He then realizes that he has thousands of inbred relatives across the sea, and invites them all to come to the Chum Bucket, thinking they will all be evil geniuses like himself. However, when they arrive, he finds out they are all inbred rednecks, and comments that he's "been away from home longer than (he) thought."
He calls them to a meeting and gets them to agree to his plan in exchange for root beer. Plankton's first name is revealed to be Sheldon, which Karen finds hysterical and mocks his name. Plankton's army then attacks the Krusty Krab, tying up Mr. Krabs and Squidward in a toilet. The Planktons open the safe containing the Krabby Patty secret recipe. Before Plankton reads the recipe, Mr. Krabs pleads him not to read it, saying "There some things this world weren't meant to be seen by mortal eyes!" Plankton reads it anyway. The ingredients turn out to be:
A pinch of salt
3 tsp. of chopped onions
A cup of love
4 lb of freshly ground Plankton
Mr. Krabs says he warned him. Plankton is horrified by this, and runs away. The other planktons read it and run (except for Clem, who can't read, but Mr. Krabs orders him to get out). Mr. Krabs and Squidward manage to escape from the toilet, and SpongeBob returns from his task, and asks what happened. Squidward asks if a Krabby Patty is actually made of plankton, Mr. Krabs explains that the recipe that Plankton read is fake, and the real one is hidden somewhere "No one, not even Plankton, would ever figure out." Squidward then correctly guesses that it is under Mr. Krabs' mattress, and Mr. Krabs runs to his house, yelling "Curse you, Squidward!"
When it originally aired in the USA, this episode was shown before "Missing Identity" due to being advertised as a "special" episode.
Before it aired, many people mistook this episode to be a special or even a movie due to the nature of its advertisements.
SpongeBob only appears in two scenes: one at the very beginning and the other at the very end. This makes the episode to be one of the smallest appearances of SpongeBob in an episode ever to be aired, similar to "New Leaf," "Rise and Shine," and "Mall Girl Pearl."
Plankton's past attempts at stealing the formula shown in this episode include:
Asking nicely. Mr. Krabs said no.
Wearing a cockroach costume; Mr. Krabs stepped on him.
Drinking a potion that turned him into a cockroach; Mr. Krabs stepped on him.
Protesting to Krabs that he is not a cockroach on a picket sign ("civil disobedience"); Krabs stepped on him again.
The robot who purchases the Coral Bits has a revolving light over its "eyes," much like the Cylons from Battlestar Galactica.
Instead of saying he can't read, Clem said "For what?" in Indonesia. There were also few other lines that had been edited aside that one:
The line "You planted grass?" was changed to "You came to destroy us?" This resulting Plankton's line to respond it changed from "Grass?!?" to "Destroy?!?"
The line "Hot dog!" was changed to "Yes! Very nice!"
The line "I'm telling you, you won't be able to handle the truth. There are some things in this world that weren't meant for mortal eyes." changed to "I'm telling you. I mean it! There are purple print that you won't able to comprehend!"
For unknown reasons, some television guides say the episode premiered in 2002 when it actually was premiered in 2004. This mistake may be because the episode is copyrighted in the year 2002, but not aired on American TV until 2004. Dish Networks original broadcast also set the episode to be aired in 2002 but changed to its correct date.
This episode wasn't listed in Comcast cable guides; only "Missing Identity" was.
This error was fixed at some point.
When Plankton had broken body parts, he appeared to have similar broken body parts to a disassembled Mr. Potatohead.
In this episode, Mr. Krabs claims that Plankton has been trying to steal the formula for 25 years; however, in "Spy Buddies" (which aired three years after this episode), he claims that Plankton has been trying to steal it for 20 years. It's possible that "Spy Buddies" took place before "Plankton's Army."
When Mr. Krabs said "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 Mr. Krabs' office was shown; but when the robot showed up, the door was gone, then when Mr. Krabs and Squidward walked outside, the door was 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 is standing on the phone book, when he says, "or 100," he is next to "S. Plankton," but when he says, "or 1000," he is next to "O. Plankton."
The phone book does not contain phone numbers.
Outside the Krusty Krab there are millions of Planktons surrounding the restaurant, but after Plankton retreats to the Chum Bucket, there are fewer of them.
When Plankton ran from the Krusty Krab back to the Chum Bucket, the road is much more curved and longer than usual.
When SpongeBob came back after Plankton's cousin's ran away, he wasn't wearing his Krusty Krab Employee Hat, but in the next scene, he is.