After unwittingly saving Springfield from an out-of-control fire, Bart is rewarded with a driving license. However, he gets bushed of driving Homer everywhere, so he goes on the run and has a relationship with an older girl named Darcy. Meanwhile, Lisa invents a fake Native American tribe for a school report and claims to be a descendant of it. The statement snowballs to a dramatic conclusion.
Lisa has to embelish an essay about her heritage for a class project, she plans to write about Native Americans, and chooses to pick a tribe of her own invention (named the Hitachi after the family's microwave). However, when reading her "tribe's" history, she becomes embarrassed at having told a lie (including stereotypes) and rushes out of the hall in a frightened manner. Superintendent Chalmers says that it must be the battle cry of her tribe, and quickly asks Principal Skinner to get him some coffee.
In the meantime, at the Spuckler farm, Cletus is milking his cow and tends to a bucket of rum. After pulling the tail of a cow to milk it, the cow kicks a chicken, knocked into a pile of crates, which causes an egg to roll around, instantly hatching into a chick when it rolls right into the blade of an axe's sheath. The chick, disoriented, wanders out of the barn, only to be snatched up by a hawk. The same hawk eventually is forced to let go of the chick when it is ensnared by a bald eagle. The chick falls into the chimney, which causes it to roll a burning log all the way back into the barn (startling Brandine along the way), starting a fire. In contrast to the famously rumored origins of the Great Chicago Fire, Cletus' cow actually succeeds in extinguishing the fire by kicking over a bucket (after the newborn chick pulled on one of its utters). Surprised, Cletus drops his lit pipe on the hay, starting a similar Rube Goldberg-esque wildfire around Springfield. The townspeople attempts to extinguish it, but they are not successful. At Springfield Elementary, Principal Skinner tells Groundskeeper Willie to get the fire extinguishers, but they have been stolen. Apparently, Bart has been preparing to use them for a wild ride on his wagon. Nevertheless, while the wagon rockets around town, the foam released from the extinguishers puts the wildfire out for good, Bart gets cheered by everyone, then is told by Mayor Quimby that Springfield will grant Bart one wish. After careful thinking, Bart proclaims that he wants a driver's license.
Bart starts using Homer's car for driving and Homer gives him a phone with his number in it. Homer calls Bart numerous times to do errands such as getting a lift late at night from Chinatown. Bart becomes frustrated and takes off to North Haverbrook, where he meets a 15 year old girl named Darcy (voiced by Natalie Portman), and convinces her that he is 16. They quickly begin a romantic relationship and Darcy soon proposes marriage. At the Court house, Bart reveals his age, whereupon a shocked Darcy reveals that she is pregnant, causing Bart to try to flee in the car (which doesn't start). Darcy tells Bart that the baby is not his, and belongs to a Norweigan exchange student, who "left back to Norweiga" then starts crying since marrying Bart was her last chance of having a proper life for her child. In an act of uncharacteristic and oddly mature chivalry, Bart agrees to marry Darcy, although she is skeptical since Bart is only ten. However, the clerk at the local courthouse tells them that in Utah, marriage restrictions are known to be a 'little loose'. So the pair takes off to Utah (where Bart is forced to deal with the horrors of Darcy's pregnancy hormones shown when she screams at him that she needs strawberries despite the fact that they were in the middle of the desert). Eventually, Homer, Marge and Darcy's parents catch the pair to foil the wedding proposal, realizing that they are too young to get married. Darcy's mother reveals that she is pregnant herself, and the family agrees to pass the two babies off as twins so as not to reveal Darcy's sin. Darcy and Bart finish their relationship, while Bart, (in his own way) assures her they will meet again, to which she agrees. Later, Bart admits to Homer that he looked forward to being a father, and they end up driving happily while singing "Twinkle Twinkle Little Star" in the night.
Meanwhile, when Lisa struggles to find excitement and intrigue in her family heritage for a school presentation, she plans to take creative license. Inspired by Bart's "Indian butter trick" and the kitchen curtains (that have corn on them), Lisa claims to be Native American, from the Hitachi tribe (named after the brand of the family's microwave oven). What begins as an innocent embellishment quickly turns into a web of lies when Lisa is chosen to represent the school and her "people" at City Hall, then as a keynote speaker for the National Native American Tribal Council. She eventually admits that she had given false information about her heritage, which compels others to admit they are not Native Americans as well. Homer compares Lisa to CBS News in a reference to the 2004 Killian documents controversy. He also mentions at the end that his great-great-grandmother actually was a Native American, much to Lisa's chagrin.