Bart trades places with a rich boy named Simon who looks just like him, but he discovers that Simon's half-siblings are planning to do him in to get his inheritance.

!! Tropes:

* PrinceAndPauper: Bart and Simon
* WeWantOurJerkBack: Albeit Lisa was reluctant to admit it to Simon.
* WouldHitAGirl: When Lisa hit Simon, she told him Bart would have hit her back in retaliation.
* WouldntHitAGirl: It came as a shock to Simon that Bart would.