Bank janitor Ernest P. Worrell is called to jury duty and soon finds himself in trouble when the lookalike defendant's attorney arranges a switch and has Ernest sent to prison in his client's place. While Ernest struggles to deal with prison life, his criminal double decides to use Ernest's job at the bank as an opportunity to rob it. Will Ernest be able to break out of prison in time to stop the robbery and expose the mix-up?

Only Ernest P. Worrell could show up for jury duty and wind up serving time in the slammer. When a crooked lawyer spots him and realizes that he is a dead ringer for his crime-boss client, the switch is on before you can say "here comes the judge."