While bathing, Mr. Burns almost kills himself and chooses to find an heir. He sees it in the form of Bart Simpson and coerces the young Simpson into staying with him.
After nearly drowning in his bathtub (due to the weight of a wet sponge upon his head), Mr. Burns realizes that if he had passed away, there would be no one to look over his power plant, so he plans to hold tryouts for local kids to be his heir. Burns rejects Bart in a special way, by using a machine to kick him in the butt. He gets revenge on him by smashing his windows, breaking his statues, and filling his car with water. Mr. Burns notices his evilness and makes Bart his heir.
Homer eagerly accepts, although Marge feels that since Bart will be inheriting Burns' money, he should spend some time with him. Bart does and initially hates it. Burns tries to get a pizza delivered by Krusty the Clown to cheer Bart up. However, he clicks the wrong button and it ties Bart down to his chair and gags him with metal bars. After setting him free he clicks the correct button and Krusty delivers his pizza. Bart then begins to love living with Burns as he gets his way all the time. Once he returns to his family's lifestyle, Bart becomes irritated that he can't get his way all the time, and returns to Burns. The family tries to get Bart back, but the police and attorney Lionel Hutz prove to be no help, especially with the court declaring Bart to be Burns' biological son. Homer and Marge then hire a Private Investigator deprogrammer to brainwash Bart into going back with them, but the effort fails when the deprogrammer mistakenly grabs Hans Moleman, whom Homer comes to like.
Bart starts to feel lonely and wants to go back to his family. Burns, however, does not want Bart to leave, and shows him a video in an attempt to trick the boy into believing that his family hates him. The family in the video, however, are actually actors. This works, and Bart comes to declare Burns as his true father. The two then celebrate by heading over to the Nuclear Power Plant, where they proceed to fire employees by dropping them down a trapdoor. This goes on until Burns attempts to make Bart fire Homer in an attempt to make him permanently sever his ties with his old family. Bart refuses, and instead attempts to fire Burns, dropping him down the trapdoor instead. Smithers, being the ever-loyal servant that he is, jumps in after Burns.
With his ties to Burns now severed, Bart moves back in with the other Simpsons, where Marge makes the point that the real Simpson family members truly missed Bart. After a heartfelt reunion, the episode ends with Homer introducing Bart to his "new brother", the still-brainwashed Hans Moleman.
As the credits begin to roll, Marge tells Homer that she wants Moleman out of the house.
Behind the Laughter
In "The Simpsons 138th Episode Spectacular", a deleted scene that was supposed to be in "Burns' Heir" was shown. When Homer turns up to Burns Manor asking for Bart, Mr. Burns deploys a robotic Richard Simmons which begins playing "(Shake, Shake, Shake) Shake Your Booty". Homer runs away, and not long after that, the robot begins to go haywire. Waylon Smithers tries to shoot it but to no effect, and Burns, Smithers and Bart take cover in the mansion before it explodes.
The reason this scene never aired was because during test screenings, the show's writers did not find the scene funny.