The Simpson family are busy preparing for Bart's birthday party. Homer sees a commercial on television for a prank microphone called the Superstar Celebrity Microphone that can be used to tap into localized AM radio systems and instantly decides to buy one for Bart. Subsequently, Bart experiences a crushingly disappointing birthday party when all his gifts turn out to be useless things like a cactus, a label maker, and a new suit. At first, he is also disappointed by the microphone, but later finds a use for it in creating practical jokes, such as tricking Ned Flanders' boys into believing that God is talking to them, listening in on Lisa and Janey's conversations about boys, and persuading Homer that martians are invading the Earth.
Bart plays a prank when he throws a radio down a well and speaks through it with the microphone, tricking the townspeople into thinking an orphan named Timmy O'Toole has fallen down the well. Although they are unable to get "Timmy" out, as the well is too small for any adult to fit in, the entire town offers moral support and do everything they can to give him hope. Krusty even gets musician Sting to join other celebrities in recording a charity single, "We're Sending Our Love Down the Well". However, Bart—after realizing that his name is on the radio thanks to his label maker—falls into the well while trying to retrieve it. When the townspeople find him, he admits that Timmy O'Toole does not exist. Angry at being tricked, the townspeople leave Bart in the well. After this, "We're Sending Our Love Down The Well" dramatically falls off the number one spot all the way down to 97, supplanted at number one by "I Do Believe We're Naked" by Funky C, Funky Do.
Despite efforts by Homer and Marge to mobilize a rescue operation, the entire town remains outraged at Bart and are disinclined to help. After Bart cries, Homer finally has had enough: he decides to dig a tunnel and rescue Bart himself. Groundskeeper Willie sees this and joins Homer, starting an excavation operation. Bart is finally rescued (with help from Sting), and Willie puts up a small warning sign near the well the next morning to prevent future incidents instead of boarding the well up instead.