Lisa's babysitting reputation is tested when she is assigned the task of babysitting Bart and Maggie, for which Bart is determined to make Lisa's life a living hell.
Marge and Homer find out that Squidport is reopening and they decide to make it a date. Meanwhile upstairs, Lisa and Janey are inspired by reading The Babysitters Club, Lisa decides to start a career in babysitting, even putting an ad in the church bulletin. At first she becomes concerned when no one calls on her to babysit. Her mother tells her the reasons people aren't hiring her is because they hire teenagers since they know what to do. Lisa tries to insist that she is more than capable of babysitting. Moments later Ned Flanders comes over and tells Homer that Maude and her mother are in a sticky situation and has to go to Capital City, so he asks Homer to watch the boys. Lisa however says that she could do it, and while he is hesitant, Ned lets Lisa watch the boys. After a successful babysitting night, Ned is impressed and recommends her to everyone. Soon she babysits Ralph and Doctor Hibbert's children. After many successful jobs, Homer and Marge decide leave Lisa in charge of Bart and Maggie while they are out, and while Bart tries to protest, his parents will not budge. Bart becomes outraged with the proposition, so he plans to 'teach' Lisa a lesson that he is not so easy to babysit. First, he refuses to eat his dinner. Next, he watches TV without Lisa's approval. He feeds Maggie ice cream with caffeine in it, causing her to run rampant in a hyper state. Then, he makes outrageous orders by phone, including a massive sandwich and hiring Krusty, leaving Lisa to answer the door for each one. Lisa is finally outraged at Bart, when Lisa finally orders him to go to bed, Bart goes to the kitchen and eats bread, claiming Lisa told him to go to bread. At that point, Lisa is about ready to snap.
Outraged, Lisa starts chasing him around the house, and accidentally knocks him down the stairs, causing a large lump to form on Bart's head and giving him a dislocated arm. However, despite the dislocated arm and the bump on his head, Bart continues to make baby-sitting hard for Lisa. Bart locks himself in his room, preserving his injury to show their parents. He then bangs his head against the door 'to make the lump bigger', causing him to fall unconscious.
Lisa considers calling Dr. Hibbert for help, but cannot as the 911 operators think that this is another prank. She realizes her reputation as a babysitter will be ruined - Lisa decides she must get Bart to a hospital without anyone knowing. She finds Dr. Nick's number in the phone book, and climbs into Bart's room via a tree to recover him. She pops him in a wheelbarrow, along with Maggie, locked in a pet cage to keep her stable.
At the emergency clinic, Lisa can't get Bart an appointment, so she plans to take her cargo to the hospital by foot. After avoiding discovery by Chief Wiggum, Bart falls out of the barrow, sliding down a muddy hill. Lisa follows with Maggie and the barrow, only to have a searchlight turned on her. She has ended up at the Squidport opening Marge and Homer were attending, along with many Springfield residents, Dr. Hibbert included. The panicked onlookers assume Bart is dead, Lisa is on drugs and Maggie was being taken to be drowned. This is quickly debunked by Hibbert and telling them that Lisa is a bad babysitter.
Bart gets treated for his injuries, apologizing to Lisa for being a jerk and ruining her babysitting business. She later gets calls from Dr. Hibbert and Ned Flanders, asking her to babysit for them, despite her mishap with Bart and she smiles.
The episode received mostly positive reviews from critics, but mixed reviews from fans which would later become negative reviews.