The episode begins with the Narrator explaining the Bikini Bottom Jail, mainly its newest member, Plankton. The warden lets all of the prisoners out, including Plankton. Plankton hears SpongeBob calling out to him. Plankton wants to know what is SpongeBob doing there and SpongeBob says that Mr. Krabs told him to watch over Plankton. Plankton does not like the idea but the prison warden tells him to quiet down. The scene changes over to a room where Karen is about to send over a cake to SpongeBob which is for Plankton. Plankton asks if Karen had put the file in the cake but Karen just laughs for she thought he was joking (although plankton was expecting her to put a file in the cake). Plankton unsuccessfully tries to jump over the glass but SpongeBob grabs him.
In the cafeteria, Plankton attempts to eat his food but a purple cellmate grabs some of his food and eats it. Another green cellmate drinks Plankton's milk and then Plankton gets eaten by a Light Blue Cellmate. Plankton yells out that he is the most evil genius and yells out his name. The Purple Cellmate, thinking the Light Blue Cellmate is talking, does not believe him, saying he and the others are fans of Plankton. Plankton calls out his name again and then the Purple Cellmate punches the Light Blue Cellmate in the stomach which causes Plankton to be punched out and crash into the wall. The Purple and Green Cellmates start to beat up the Light Blue Cellmate until Plankton breaks it up. Plankton introduces himself to the Cellmates and the Cellmates say how they are going to do everything that Plankton says. Plankton gets excited saying how easily he could get the Krabby Patty Secret Formula.
Outside, Plankton is explaining to his Cellmates how to escape from the Bikini Bottom Jail. The Cellmates have ideas but Plankton tells them they need better ones. The Whale Cellmate says they could break out only if they had chum and the other Cellmates agree. Plankton is surprised with the Cellmates saying how chum is great for committing crimes. Plankton asks if chum is great for eating but the Cellmates do not think so. Plankton then agrees to make chum for the Cellmates and they all cheer. Inside Plankton's jail cell, Plankton, and his Cellmates are creating chum using different kinds of items. They successfully make the chum. SpongeBob overhears them and runs to the Krusty Krab to warn Mr. Krabs. At the Krusty Krab, SpongeBob tells Mr. Krabs that Plankton is planning to break into the Krusty Krab with his Cellmates. Mr. Krabs insures SpongeBob that he will handle the problem.
Back at Bikini Bottom Jail, a Prison Warden is talking to two of Plankton's Cellmates saying why they are out of their cells. The Purple Cellmate says that the Green Cellmate said the napkin smells like kelp berries. The Prison Warden smells the napkin and falls down, unconscious. The Purple and Green Cellmates bring the Prison Warden inside while Plankton arms himself with chum and a bomb. The Whale Cellmate then launches Plankton to the other side of the prison and Plankton plants the bomb on the wall. Plankton gets spotted but the bomb goes off and blows a giant hole in the wall. However, the Prison Wardens then start filling up the wall, making it impossible for Plankton to get, though. However, they get stuck and Plankton uses the opportunity to lead all of his Cellmates out through the front door. At the Krusty Krab, SpongeBob notices Plankton and all of his Cellmates preparing to invade the Krusty Krab. Mr. Krabs says that they are ready for them while Plankton yells out to his Cellmates to bring him the formula. Plankton's Cellmates begin breaking down the door using the Whale Cellmate as a battering ram and they successfully break in. The Whale Prisoner then opens the safe with Mr. Krabs urging Plankton not to get it but Plankton does not listen. As Plankton heads toward the "formula," the curtain rises and the entire Bikini Bottom Police Force emerge from it. Mr. Krabs revealed that he knew of Plankton's attempted break in and had enough time to hide the entire Police Force in his safe. The Police Force then take Plankton and the rest of his Cellmates back to jail. SpongeBob congratulates Mr. Krabs on how he always wins, but then the entire Krusty Krab falls apart. The episode ends when Mr. Krabs replies "Yep, I'm a winner."
One of Plankton's cellmates is a whale that looks like Pearl Krabs. Although, he does not have her hair or lipstick.
Plankton was not afraid of the whale in this episode, but he was afraid of Pearl in "One Coarse Meal." He might not have been afraid since this whale was working for him, or that he was able to overcome his fear of whales.
It is unknown the exact reason why Plankton is in jail, though it could possibly be due to attempting to steal the Krabby Patty Secret Formula.
The recipe for chum in this episode is different than that revealed in the episode "Spongicus." This could be due to Plankton altering the formula to make chum more edible.
Chum is actually the guts and organs of fish, yet this was not used in the recipe.
It is revealed that chum is used to commit crimes throughout Bikini Bottom.
Plankton asked if Karen had inserted a file in the cake. He really could have gone through the drawer that Karen put the cake through to get out but perhaps he knew he is too small to push it open and there to many witnesses around.
This is one of few episodes where SpongeBob calls Plankton by his first name "Sheldon."
Although Squidward did not appear in this episode, a prisoner used chum and looked and laughed like him.
Running Gag: Plankton getting poked by a police baton.
Even though Karen points out the silliness of having a nail file in a cake, one of the prisoners is seen with a nail file and a cake in his stomach when he eats Plankton. The cake even looks like the one Karen brought Plankton it might be possible its the same cake or one that is identical to it.
The original German title of this episode, "Fraß macht frei" (Chum Sets You Free), was cancelled 10 days before its premiere on Nickelodeon Germany, due to the reference to a German phrase "Arbeit macht frei," known for appearing on the entrance of Auschwitz and other labor camps. However, the episode premiered with the title unchanged which resulted in banning the episode. On August 1, 2015 (approximately four months after the German premiere), the episode finally reran with a new title "Knastbrüder."
Plankton using a toilet in jail to make chum is similar to how Mojo Jojo created the Rowdyruff Boys from the original Powerpuff Girls series.
Plankton's prisoner number is #655321, which is a reference to the character Alex in the book/film A Clockwork Orange who shares the same number.
Early in the episode when Dennis emerged from his cell, he was tall. After he and some other prisoners help break into the Krusty Krab, Dennis was much shorter.
Plankton mentioned that the people of Bikini Bottom were to be free from cruel and unusual punishment ("Excuse me, doesn't this count as cruel and unusual punishment?"). However, it has been shown that characters had been subjected to it in the past such as Squidward ("Little Yellow Book") and Patrick ("The Smoking Peanut").
When the Whale Cellmate turns around and looks at the safe in the Krusty Krab, SpongeBob pants leg color is white instead of brown.