It's show-and-tell day at Springfield Elementary School, and seeing how most kids have geodes or other random items, Bart brings his dog, Santa's Little Helper, to school. Everyone is excited to see Bart's dog, but Santa's Little Helper shortly makes his way through the school vents, when he is put away in a closet and is noticed by Ralph Wiggum. Groundskeeper Willie is covered in grease and sent into the vents and retrieves the dog (his foot getting tickled and the kids who can hear him laughing throw objects at the vent where he was) after informing Principal Skinner who is talking on the phone, but Superintendent Chalmers shows up, in detest after hearing about the dog. At first, Chalmers looks into Santa's Little Helper's eyes and forgives Skinner for what has happened. But after a falling Willie lands on the "bloated gasbag," this is the final straw. Chalmers fires Skinner on the spot, and Bart is guilty because of his dog.
Skinner rejoins the army, but manages to gain a friendly relationship with Bart, even going out to Luigi's to eat. During these events, Ned Flanders becomes the new principal, and is very lax with the rules. Due to this, the school breaks out in chaos and the kids vandalize, tag and even kidnap and lock Martin Prince in a cage and force him to do ironing. Bart feels bad for Skinner, and wants to try to get Flanders fired. Superintendent Chalmers shows up to do another inspection of the school, and Bart convinces him to fire Flanders because of the chaos the kids can make with impunity. Chalmers then hears Flanders ask the students to "thank the Lord" over the intercom, and because you're not allowed to promote a religion in public school, Ned Flanders is fired and Skinner becomes principal again. Skinner and Bart know that they are no longer friends now that Skinner is principal again, so they say goodbye and walk off, feeling good about other.