Brian begins to think he's not so smart when he takes the SAT'S for Meg and gets a low score, so Peter decides to show him the joys of being an idiot.
- Meg worries about passing her SAT to get into college and Brian reassures her. But at school her worries continue and her friends suggest she get a smart person to take the test for her. Neil Goldman takes a pass, which leaves Brian as the only candidate. She butters him up and asks him to take the test for her. Brian hesitates but is won over by a quote from his book. At school, Brian successfully poses as Meg but when the test results are returned, she lets him know they failed badly. The news that Brian failed becomes ripe fodder for teasing, until Peter tries to get him to look on the bright side of being stupid. They take part in dumb people stuff like demolition derbies, slapstick, Florida, and Peter's dumb antics.
However, Stewie is puzzled about Brian's change in attitude as being very uncharacteristic of him. When he collapses with a bloody nose, he goes to the hospital and it is discovered that he has a brain tumor. Flustered with trying to get an answer out of Dr. Hartman over his condition, Lois finds out that the tumor is benign. They are split on whether or not Brian should have the surgery, with Brian wanting to leave himself be while Stewie wants his old Brian back. Stewie exposes Brian to his cultured items trying to get him to remember what his life was like originally. However, Brian fully embraces being dumb and Stewie gives up, leaving him resigned to living with the new Brian. But when Peter's stunts worry Stewie that it could lead to Brian's death, he is filled with new resolve. Deciding to use his stupidity against him, he tricks Brian into getting the operation and he is returned to his normal pretentious self.