The family take Bart to dinner at the Singing Sirloin restaurant (as seen in "Life on the Fast Lane") for getting his first "A" in an astronomy quiz. When asked how he achieved this rarity, Bart explains that he was in Mrs. Krabappel's class trying to force a hamster and a lizard to mate, but was forced to hide in the coat closet when he saw Krabappel and Principal Skinner making out, and needing to get his mind off this, he studied a chart of the Solar System on the closet wall. The family's feeling of pride does not last, though, as a waiter tells Homer that the credit card he has attempted to use for paying the meal has been rejected. The family responds by trying to run away, but are stopped and made to sing and entertain the other customers in the restaurant to work off their debt. At the end of the night, as the family are driving home, Bart and Lisa notice that the back seats and floor of the car are missing, and Homer explains that he had to sell them for gas money (which he spent on a novelty car horn). He and Marge subsequently learn from a visit to financial planner Lindsay Naegle that the Simpsons are having severe money woes.
In the hope of sorting out these problems, Homer decides to ask his boss, Mr. Burns, for a raise. Burns, meanwhile, has decided to spend a week looking for things to amuse himself while his assistant, Smithers, is in New Mexico performing in a Malibu Stacy musical that he wrote. When Burns tries unsuccessfully to use the salad bar at the cafeteria, Homer shows him how, then sums up his courage to ask for a raise. Burns is unimpressed and, wanting a "larf", orders Homer to throw a pudding at Lenny with the promise of four dollars. Homer does so, amusing Burns so much that he decides to make Homer his "Executive in Charge of Recreation" or, in his words, his "prank monkey".
Subsequently, Burns takes Homer around the streets of Springfield, making him perform embarrassing or cruel tasks such as eating a rare Spider-Man comic in front of Comic Book Guy and pretending to be a baby in a public toilet, and paying him for each of these tasks. Then, Burns takes him to the Springfield Zoo, where he makes him put on a panda suit and masquerade as a new female panda named "Sim-Sim" in the hope of shocking onlookers when they discover the disguise. It goes wrong for Homer, though, when first he is zapped by two animal handlers, before the zoo's male panda, Ping-Ping, becomes romantically interested in "Sim-Sim" and drags "her" into his cave. Finally, when Homer tries to escape, he ends up in the skunk exhibit and gets sprayed. It is then that Lisa discovers him.
Lisa convinces Homer to stop being a "prank monkey" as his dignity is more important than money. This he does, though Burns still gives him his payment for the panda task. When Homer asks Lisa what he should do with all the money he has earned, Lisa suggests donating it to needy children, so he spends it all on toys at Costington's Department Store. Mr. Costington is so impressed by this show of generosity that he suggests that Homer dress up as Santa Claus for the upcoming Thanksgiving Day parade, distributing the toys to the kids. During the parade, however, Burns shows up and tries to convince Homer, in his Santa costume, to pull a prank on the whole town. Homer flatly refuses, only to be tempted by Burns' promise of one million dollars. Santa is then seen throwing bucketfuls of fish guts into the crowd, which results in an attack by seagulls. A disappointed Lisa watches on, remarking, "Oh, dad, you sold your soul," when Homer, back in his normal clothes, appears alongside her; it turns out that Burns is now wearing the Santa costume. Homer thanks Lisa for giving him "the gift of dignity", and the family embrace before Burns throws fish guts at them.