Lisa befriends Harper, a new kid at school who happens to be super-rich. Then, Homer befriends Harper's dad and is able to enjoy the perks of Lisa having a rich friend, as well. But Lisa decides that Harper is a bully and moves to end the friendship, which prompts Homer to try and smooth things over so he can continue to enjoy the good life.

Lisa sets out to restore the tarnished reputation of Springfield's first female inventor. To find her invention, she scours an abandoned asylum and a restaurant that caters to men. Bart joins Lisa at the asylum, stealing one of the homicidal patient's notebooks, and bragging to the boys at school that he wrote the entries himself. This revelation causes Homer and Marge to believe he is a sociopath, which Bart decides to use to his advantage until things go too far.