Simpsons Season 5, Episode 2: Cape Feare

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.