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Homer gets sent to prison for fraudulent charges of nuclear terrorism (so that Mr. Burns doesn't have to).
Mr. Burns's bathtime is rudely interrupted by the FBI, who give him an advance notice (as repayment for a previous favor) that he has 24 hours to gather all his documents and videos. When Smithers asks why, Burns reveals that he had been selling nuclear material to third-world countries to fund his vacation expenses. In order to keep Burns out of prison, Smithers takes the recorded video footage of Burns's deals and digitally edits them to put Homer Simpson in his place.
Homer is quickly arrested, convicted, and thrown into a prison cell. Fortunately, he makes a very fast friend in his cellmate Sideshow Bob (as Bob's hands have been around Bart's neck almost as much as his own). Bob offers to help Homer escape by sharing with him a secret tunnel he had dug in the solitary confinement cell before being moved.
When the two of them get into the cell, its sole occupant, a masked and restrained man of unknown identity, eerily tells Homer that he is going to kill him. Homer panics and goes into the tunnel, digging furiously until he falls into a cavern filled with boxes of old paintings. The mystery man follows and reveals himself to be Frank Grimes, Jr., the vengeful son of the power plant employeethat Homer drove to a shocking suicide, but Bob ends up falling onto him and knocking each other out.
Mr. Burns arrives and demands to know what everybody is doing in his secret stash of paintings that he had stolen during the war. Homer tells Burns that he'll keep quiet about the paintings if he can be released from prison. As Burns has no time to kill all three of them and hide the bodies before the police arrive, Burns agrees to have Homer's charges dropped. Homer is returned to his family and everybody is happy... except Marge, who has been enjoying the company of the muscular and sexy yard workers she hired to keep the house up in his absence.