Plan Z is to obtain King Neptune's crown and frame Mr. Krabs, in which the punishment would be execution. As Mr. Krabs is frozen at first by Neptune, and with SpongeBob and Patrick on the journey to Shell City and Squidward enjoying his time off, the secret formula is left unprotected, so Plankton steals it and put the Krusty Krab out of business as a result.
Customers come to the Chum Bucket, in which he uses bucket helmets to mind control them. He rules Bikini Bottom and renames it "Planktopolis." However, it is foiled by SpongeBob and Patrick making it to Shell City and back, and then Plankton is arrested, Mr. Krabs is freed, and Neptune gets his crown back.
- "Plan Z" is also the name of Adolf Hitler's plan for rearming the German Navy prior to World War II so that it could match up with the British Royal Navy on equal terms.
- As shown in The SpongeBob Movie: Sponge on the Run, Plan Z was the last plan to have an alphabet letter as its name as Plankton now gives numbers as the names of his new plans.