The Girl Who Slept Too Little is the second episode of Season 17.
When a new stamp museum is going to open behind the Simpson house, the Simpsons protest its construction to the point where it is moved to the site of the Springfield Cemetery, and the cemetery is moved to behind the Simpson house. Lisa is afraid of the things she sees, and Homer and Marge are afraid that if Lisa keeps sleeping with them, they will go crazy, but while Homer and Marge ask a psychologist for help, Lisa has her own solution: if she can spend the night in the cemetery, she can overcome her fear.
When construction for a stamps museum wakes up the Simpsons and Flanderses, everyone in their neighborhood protests against its construction. However, during his protesting cheer, Homer accidentally says his PIN number and asks everyone to forget it, but Apu, Helen Lovejoy, the Hibberts, Sideshow Mel, Lenny and Carl write it down. Soon, Mayor Quimby moves it to where the Springfield Cemetery used to be and the cemetery is moved to the backyard of the Simpson family's house. Lisa is the only member of the family who has her room close to it, and because of that, she can't sleep at night, so she ends up developing a habit of sleeping with Homer and Marge.
The next night, Lisa meets Gravedigger Billy, who is Groundskeeper Willie's cousin. After a hand comes out of a tomb, Lisa gets afraid and rushes into Marge and Homer's room, where she makes a promise to them that if they go to the Springfield Stamp Museum, Lisa will sleep in her room. The next day, at the museum, there is a lecture for Milton Burkhart's book "The Land of the Wildbeasts" and an ad that is based on the book for a restaurant called The Hillside Wrangler. Lisa then feels that she can sleep in her room with the cemetery, but she is already afraid, so she sleeps in Homer and Marge's room once again. Marge and Homer then spend a night in Lisa's room to find out how scary it really is, and they later contact a psychologist.
Marge and Homer meet a psychologist at Sit 'n Weep, where they find out that it is expensive and her fears are mostly going to be solved by herself, as she was not nurtured enough as a baby, so she had to raise herself since they were so busy with Bart and his shenanigans. Lisa, however, does not want to see a therapist, so she goes with Bart and Santa's Little Helper to overcome her fears at the cemetery, but Bart leaves and Santa's Little Helper runs away.
Lisa then changes her mind, but the gate is locked and Lisa is left alone. Luckily, Chief Wiggum, Eddie and Lou are there, but Chief Wiggum becomes alone and afraid. He takes off his clothes, and finds a Walkman under his arm, so he plays it and dances off into the mist. Later, it is revealed that he got scared and climbed and hid in a nearby tree. In the meantime, Lisa sees Dr. Nick, who is pretending to be Dr. Octopus using arms he acquired while grave robbing, and tells Lisa she has a check-up on Tuesday and Lisa replies with "we go to a better doctor". Afterwards, Lisa is confronted by an owl and runs, soon tripping over and injuring her head on a tombstone, getting knocked out unconscious.
Marge and Homer arrive home to find out that Lisa has left home and went to the cemetery. They panic and are angry at Bart, who was only watching Itchy & Scratchy and could not care less. While unconscious, Lisa has a dream, where she is swallowed by a skeleton pretending to be an elderly woman. She then finds herself stuck on a spider's web and confronted by a giant spider with Bart's head, where he tells her to meet her new 'boyfriend'. A slug resembling Milhouse slithers forward and attempts to impress her with his slime buildings.
Lisa screams and appears in the "Land of the Wildbeasts", where the beasts come across as funny to her and teach her that it is ok to be scared, regardless of how 'smart' she is. Eventually, Marge and Homer find Lisa, wake her up, and go back home. However, Chief Wiggum is still clinging to the tree in the nude, and Lou is unable to pry him from the tree and resorts to using a pizza bagel to get the chief down. With no explanation given, Wiggum has suddenly teleported on the ground behind Lou, fully clothed and back to normal.