When Bart steals actor Denis Leary’s cell phone, Marge uses its built-in GPS signal to track her son… leading the family to the ancient ruins of Machu Picchu.

As Principal Skinner drives his overbearing mother along a freeway, his car runs out of gas. From an overpass, Milhouse spots Skinner as he tries to cross the dangerous roadway to get some fuel. Using his cell phone, Milhouse contacts his friends, and alerts them about the spectacle. As the kids gather on the overpass, Barney (who’s on prison detail) begins chasing Skinner with a litter stabber. The kids laugh at the sight. Nelson notices that Bart is missing. Milhouse tells him that Bart is unreachable: he doesn’t have a cell phone. Meanwhile, Bart suffers through one of Lisa’s imaginary tea parties. When Bart finds out that he missed the Skinner episode because Milhouse wasn’t able to reach him, he decides to take action. He begs Homer and Marge to buy him a cell phone, but they maintain it’s just too expensive. Later, a golf ball hits Bart in the head. Furious, Bart makes his way to a nearby country club to complain. Dr. Hibbert admits that the golf ball belongs to him. He gives Bart a dollar for retrieving it (as the balls cost $5 each). Bart realizes that he can earn money by collecting golf balls. Before long he’s just 20 balls away from earning enough money to buy a cell phone; but Groundskeeper Willie accuses Bart of stealing his business, and forces him to give up the idea. A depressed Bart sits on a rock as some celebrity golfers, including Krusty and actor Denis Leary, play nearby. As Leary is about to take a swing, his cell-phone rings. Furious, Leary hurls the cell phone into the air. It lands on the ground next to Bart. Bart picks it up, and decides to keep it.

Bart uses the cell phone to call Milhouse. Producer Brian Grazer calls looking for Leary. Bart tells him he has the wrong number, but Grazer doesn’t believe him. Before he hangs up, Grazer says he landed the screen rights to the book Everybody Poops. Grazer wants Leary for the part of a constipated gorilla. Bart (impersonating Leary) commits to the part. After Bart hangs up, Milhouse worries what Leary will do when he finds out what’s going on. Bart uses Leary’s phone to make numerous crank calls around the world; phoning bars in Hawaii, Australia, and Sweden. Leary phones Bart, and promises to rip his heart out when they meet. Milhouse tells Marge that Bart has Denis Leary’s cell phone. Marge confiscates the device, and a short time later Leary calls. Marge tells Leary that she’ll return his cell phone. Leary has a better idea. He tells Marge to activate the GPS feature, and then give the phone to Bart. That way she’ll be able to track Bart’s every move. Marge takes Leary’s advice, and gives Bart the cell phone. Homer logs onto a website, and tracks Bart’s movements. When Bart enters a construction site, Marge decides to take action. She finds Bart at the wheel of a forklift. Marge continues to surprise Bart whenever he’s somewhere that’s off-limits to kids. Lisa discovers Homer and Marge tracking Bart’s movements. She tells them they’re violating Bart’s rights. Lisa tells Bart about Marge and Homer’s scheming. Bart removes the GPS tracking chip from the cell phone. After placing it inside a bread crumb, he feeds it to a bird known as a red scarlet tanager. The bird flies off. Marge and Homer react to the sight of Bart’s signal moving rapidly toward Shelbyville’s fish market. They hop in the car, and drive off. Watching from the bushes, Bart laughs a sneaky chuckle. Later, at a bird sanctuary, Homer zeroes in on the signal. He reaches into a tree, and tries to grab his son. Instead he pulls out a porcupine, which promptly lashes him with its tail.

With his family gone, Bart decides to have some fun. He invites Milhouse and Nelson over to his family’s house for some grilled Twizzlers. When day turns into night, Bart misses his parents. Homer, Marge, Lisa, and Maggie follow “Bart’s” GPS signal. The signal leads them to a field near a highway. Homer pulls over to investigate. While Homer and Marge search for the missing Bart, Lisa notices the scarlet tanager land on the hood of the car. Lisa realizes that the bird swallowed the GPS chip. She also realizes that the bird is migrating south to Machu Picchu, Peru. Lisa is more than happy to keep her discovery a secret, so that Homer and Marge will take her to the wondrous Machu Picchu. Back at the house, Bart fills his time by decapitating Malibu Stacy dolls using a golf club. He grows very afraid when night falls. Homer, Marge, Lisa, and Maggie reach the ancient ruins of Machu Picchu. An exhausted Marge falls asleep at the feet of an Incan warrior statue. As she dreams, Marge speaks with the warrior statue. He tells her about the mothers of ancient Machu Picchu, who were overly protective of their children. When the children grew up, they were no match for the armies of conquistadors who invaded the city. Marge realizes that Bart needs to learn how to take care of himself. A short time later Marge realizes that the GPS signal is coming from the tanager. Marge tells Homer it’s time for them to return home. When the family arrives in Springfield, a lonely and frightened Bart clamps himself around Marge’s leg. He begs her not to leave him again. A short time later, Marge realizes that Maggie is missing. Back in Machu Picchu, Maggie is being worshiped by a group of Incans.