S05E02 - Cape Feare
After receiving numerous death threats in the mail, Bart becomes paranoid. It is revealed that the writer is his enemy, Sideshow Bob, who is incarcerated in Springfield State Prison. The next day, Sideshow Bob's parole hearing is held; the parole board is easily convinced that Sideshow Bob is no longer a threat. When the Simpson family goes to the cinema, Sideshow Bob sits in front of them and acts obnoxiously. The Simpsons then realize that it was he who sent the letters, and he was the one who threatened to kill Bart where Marge angrily tells him to stay away from Bart.
The Simpsons opt for the Witness Protection Program and relocate to Terror Lake, changing their surname to "Thompson" and settling in a houseboat. However, the family is unaware, as they drive cross-country to their new home, Sideshow Bob has strapped himself to the underside of the car.
During the night, Sideshow Bob reaches the houseboat and cuts it loose from the dock. Sideshow Bob then ties up Homer, Marge, Lisa, Maggie, and Santa's Little Helper to ensure they will not interfere with his plan. Sideshow Bob enters Bart's room, ready to kill him. Bart flees out the window and tries to escape, but he cannot jump off the boat. Sideshow Bob catches up to Bart and offers him a last request. Having noticed a sign saying that Springfield is fifteen miles away, Bart gets an idea; he compliments Sideshow Bob on his beautiful voice and asks him to sing the entire score of the H.M.S. Pinafore, to stall for time as the houseboat floats to Springfield. After the performance, Sideshow Bob advances on Bart again, but the boat runs aground, interrupting Sideshow Bob before he can finish him off. Sideshow Bob is arrested, and the Simpsons return home.