"American History X-cellent" is the seventeenth episode of Season 21, which aired on April 11, 2010. The episode was written by Michael Price and directed by Bob Anderson. The episode features several references to Stephen King's The Green Mile and The Shawshank Redemption.
When stolen paintings are found in Burns Manor, Mr. Burns is arrested, so he has Smithers take over duties at the nuclear plant, but when he starts working the employees night and day, they try to get Mr. Burns back, even if it means breaking him out of prison - which it does; Bart and Lisa bond over one ant that survives an accident involving Lisa's ant farm.
Mr. Burns celebrates the Fourth of July in his typically despotic way - by using his workforce as slave labor for a picnic. He is unimpressed by their efforts, which leads to Lenny, Homer and Carl getting drunk in his wine cellar and destroying his study. When Burns calls the cops, they focus not on his employees but on the fact that he possesses art stolen in an infamous (and taken-from-real-life) heist from the Isabella Stewart Gardner Museum in Massachusetts. Burns tries to bribe his way out of jail but gets imprisoned, where he changes his ways due to the guidance of a fellow inmate, and by influence meaning literally sucking out the evil from Burns and eating it (both the character and his power parodying John Coffee of The Green Mile by Stephen King).
Mr. Smithers is placed in charge of the plant in his absence, where he initially proves an improvement over Mr. Burns. Unfortunately, he catches Homer, Lenny and Carl mocking him behind his back at the bar, resulting in him turning into a tyrant and the three friends launching a mission to spring Burns from the penitentiary. But does Mr. Burns want to return to his old ways?
Meanwhile, Bart and Lisa, left to their own devices because Homer’s so busy at the nuclear plant, reluctantly team up to care for an ant farm; when a fight between them results in all but one of the ants being eaten by Santa’s Little Helper they take special care of Annie, the sole survivor, and must choose between letting her live out her dotage in the wild or keeping her in captivity.