When a new stamp museum is going to be opened 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'll go crazy, but while Homer and Marge ask a psychologist for help, Lisa has her own solution: if she can make it until midnight without calling the Corey hotline - wait, wrong episode - if she can spend the night in the cemetery, she can overcome her fear.
When stamp museum construction wakes up the Simpsons everyone in Springfield protests against its construction. Soon Mayor Quimby moves it to where the Springfield Cemetery used to be and the cemetery is moved to the backyard of The Simpsons' house. Lisa is the only member of the family who has her room close to it. Lisa then can't sleep at night and ends up making a habit of sleeping with Homer and Marge.
The next night Lisa meets a gravedigger resembling Groundskeeper Willie known as Gravedigger Billy. After a hand comes out of a tomb Lisa goes to Marge and Homer's room and makes a promise that if they go to the Springfield Stamp Museum Lisa will sleep in her room. When they get they're they find Lenny making a fortune using his yard as a parking lot much to Homers jealousy (not remembering having campaigned against the museum before.). At the museum there is a lecture for Milton Burkhart's book "The Land of the Wildbeasts" and an ad 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 is already afraid and sleeps in Homer and Marge's room. Homer and Marge then come back from a night with Apu and Dr. Hibbert and Marge tells Lisa she is breaking her promise (via "I Spy") however Homer mistakes it for the real game. Marge and Homer then spend a night in Lisa's room to find out how scary it really is and they contact a psychologist.
Marge and Homer then try to contact a psychologist and 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 and had to all but raise herself since they were so busy with Bart. Lisa, however, does not want to go see a therapist and goes with Bart and Santa's Little Helper to overcome her fears at the cemetery but Bart leaves and SLH runs away. Lisa then changes her mind but the gate is locked and Lisa is left alone. Luckily Chief Wiggum and Eddie and Lou are here but Chief Wiggum becomes alone and afraid. He takes off his clothes, and finds a Walkman under his arm. 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. Lisa in the meantime 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. She then faints. Marge and Homer get home to find that Lisa has gone to the cemetery. They panic and are angry at Bart who was only watching cartoons and could not care less. Lisa then finds herself in 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. The spider then 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 a different location. She is in the "Land of the Wildbeasts". The beasts come across as funny to her and teach her that it is ok to be scared, regardless of how 'smart' you are. Marge and Homer then find Lisa and wake her up and they go home, happily ever after. Chief Wiggum is still clinging to the tree in the nude. Lou can not prise him from the tree and resorts to using a pizza bagel to get him down. In a flash, Wiggum is fully clothed and ready to go.