Homer, Lenny, and Carl decide to skip out on work to see the Springfield Isotopes and, more importantly, drink all the cheap beer they're selling. Milhouse also heads out to the game, but is more interested in the free baseball cards that will be given away to the first 500 attenders. Bart hardly cares about this, but decides to go since it means he'll get to skip class.
As Bart and Milhouse arrive and claim their cards, the boys head down to meet the players. One of them, Big Bill McCloskey, tricks them into calling player Willy Dipkin "fishface." The prank leads to Bart and Milhouse getting ejected from the game. As revenge, Bart quickly writes something on Dipkin's bat and leaves with Milhouse while Dipkin is getting his picture taken.
Homer tapes a picture of himself (upside-down) onto the camera to make it look like he is still at work to cover his absence, then heads out with Lenny and Carl to the stadium waiting for the game to start. Homer ends up falling asleep after drinking an oversized Duff. When he wakes up, he finds that the game has been done for an hour and panics, as he must get back to the Power Plant by 5:00 to clock out.
Back at the Power Plant, Smithers and Mr. Burns spot Homer's upside-down picture on the surveillance televisions and orders the surveillance crew to make repairs. Homer barely manages to beat them to his post and avoid getting into trouble, but he doesn't notice the picture fall off and hit a button on his console, which ends up shutting off a sub-grid. Among the places without power is a warehouse of frozen vending machine food, which spoils overnight due to the freezers dying.
The next day, half of the teachers at Springfield Elementary eat the tainted snacks and receive food poisoning, and so substitute teachers are forced to fill in for them for the rest of the week. Lisa's new teacher is very strict on her and demands mindless conformity to her many rules, while Bart's is easygoing and interprets his poor work as a way of expressing his creativity. Both kids feel upset, but decide to make the most of it as the school's Arts and Crafts show approaches. Bart brings in a stick hoping his new teacher will interpret it in some way, but he interprets it as being a copy of Marcel Duchamp's work and gives Bart an F. Lisa brings in a sand casting which represents many races and cultures joining hands, but her teacher misinterprets it as an anti-multicultural theme and gives her an A. Marge consoles both kids afterwards by telling them that they at least stayed true to themselves, while the tainted food is destroyed by hazardous waste teams.
At school the next morning, the new baseball cards have arrived, one of which is Willy Dipkin. It is revealed that Bart wrote "fishface" on his bat. As a result, the cards got pulled off the market and only a few got out, making them rare. Everybody's laughter ends when the regular teachers return, and the status quo is back once again.