Bart starts receiving threatening letters in the mail and it is soon revealed that they were sent to him by Sideshow Bob. Bob is released from prison, so Bart is placed in the Witness Relocation Program and the Simpson family is moved to Terror Lake. However, Bob follows the Simpsons there and sneaks onto the family's house boat and tries to kill Bart. Cornered, Bart asks Bob to sing the entire score of HMS Pinafore as a last request. Bob does so, and during his performance the boat drifts through Springfield and Bob is caught.