Dr. Nick Riviera is confronted by Dr. Hibbert and a board of medical practitioners who are threatening to have his medical license taken away. Dr. Nick argues that his morally-questionable medical practices are an important part of life in Springfield, as he explains through three short stories.
In his first story, Patty and Selma go in for a perm and are warned that they should not smoke until their hair fully dries. Naturally, this warning goes unheeded and their hair catches fire. When it cools, the sisters find that their smoldering scalps are fused and they are stuck together. Though they try to make do at first, the sisters are forced to turn to Dr. Nick to free them. It works, in that their hair is completely removed, and Patty and Selma are left with bald noggins that flatters Homer.
For the second story, Comic Book Guy gets knocked in the head while reaching for a box of comic books. When he comes to, he suddenly becomes disgusted at the sight of the overpriced collectibles and the greasy nerds buying them. Dr. Nick diagnoses that the "nerd center" of his brain has been damaged, and Comic Book Guy will never be the same again. For a while, he lives a fulfilling life. He closes The Android's Dungeon, gets in shape, and even finds a girlfriend, but he cannot help but miss his old lifestyle. Eventually, Dr. Nick prescribes the cure: a brain transplant, with a clone-brain grown and donated by Prof. Frink. Soon, Comic Book Guy is back to his old self, though now in a green lab coat and with familiar "glavins" and "ga-hoys" in his speech.
Finally, Krusty the Klown arrives in the annual San Diego Clown-Con and sees an exhibit where British clown scientists are training monkeys to be perfectly-obedient sidekicks by making them watch horrible daytime television non-stop. One of the enraged monkeys breaks loose and bites his handler, who then rabidly bites another clown. Twenty-eight hours later, an epidemic of rabid zombie clowns is running through Springfield, biting every clown in sight and turning them into more zombies. Krusty barely escapes getting nipped with help from Dr. Nick and Prof. Frink. They tell him that the zombie virus is mutating to affect clown sidekicks and other lesser forms of comedian and will soon spread to normal people if not stopped. When Krusty explains how it began, Dr. Nick suggests that a bite from a happy monkey can counter the virus. The only monkey Krusty has is Mr. Teeny, who is currently copping an attitude from a previous argument with him. When Teeny hears that he'll get to bite Krusty, he happily sinks his teeth into him, and Krusty in turn bites the zombie clowns back to normal.
As Dr. Nick finishes up, he explains that his purpose is to do the things other doctors couldn't, shouldn't, and wouldn't do. This gets Dr. Hibbard's approval and Dr. Nick is allowed to keep his license. However, he is also asked to stop moonlighting as a veterinarian, or at least to only use body parts from the same animal when performing transplants.