The Griffins invite their neighbors over for game night. While playing Trivial Pursuit, Lois uses questions from the preschool edition for Peter in order to let him win. When Peter wins, he brags to everyone, believing himself to be smarter than the rest of the family. Irritated at Peter's arrogance, Brian challenges Peter to take the MacArthur Fellows Program test to prove he is a genius. The results of the test show that Peter is not a genius; in fact, they indicate he suffers from mental retardation. Peter sinks into depression after being publicly labeled as retarded. While driving home with Lois, Peter accidentally knocks down Tom Tucker. Tucker, recognizing Peter as "the retarded fellow", does not press charges, and Peter realizes his condition means he can get away with anything.
While testing the limits of what he can get away with, such as interrupting church attendants by having a Bible fight, kicking open the stall doors in a girls' bathroom, and saying "testicles" through a microphone at a fast food restaurant, Peter goes behind the counter and sees a "Fryolator" and wants to take it home. However, he accidentally drenches Lois with boiling oil. While she is recovering, Child Protection Services takes away Peter's custody of Meg, Chris, and Stewie on the grounds that Peter is mentally unfit to look after them. The three are placed in the care of Cleveland. When Brian tells Peter that he just has to show that he is a good parent, Peter thinks that the best way to do that is to show what a bad parent Cleveland is, so he brings seven prostitutes into Cleveland’s house. This does not work as Agent Jessup sees through the plot and Cleveland orders Peter and five of the prostitutes out. In a last attempt, he appeals to the court for custody of the children, but he is denied and avoids imprisonment only because the judge forgets that prisons exist. After returning home and accepting that the Griffins may never be together again, Lois walks in, revealing she has completely recovered and reobtained custody of the children. Peter is overjoyed that everything is back to normal, as well as the fact that Lois now smells like French fries for the next 6 months.