When a new, tough-looking kid at school named Donny teams up with Bart to help him carry out his pranks, Bart thinks he has found his ultimate partner in crime. However, when Bart's seemingly foolproof pranks begin to backfire, Groundskeeper Willie warns Bart that he smells a rat in Bart's group of friends. With Principal Skinner on his case and the possibility of expulsion on the horizon, Bart must figure out who he can trust and who he must get rid of before it is too late. Meanwhile, Homer receives a fancy loaner car after Marge damages their old car in an accident, and he grows extremely attached to his new set of luxury wheels.