The episode opens with SpongeBob and Gary sleeping. Patrick is cleaning his rock with a mop then wakes them up. SpongeBob asks him why he is doing it and he responds by saying his sister Sam Star, is coming. Patrick also reveals that they were lost in the surf when they were only kids. Squidward screams angrily and demands peace and quiet, but Sam then arrives in a bus and punches the door down. She is revealed to be a huge starfish. Sam hugs and almost suffocates Patrick. Patrick introduces SpongeBob to Sam and Sam, mistaking SpongeBob to be a danger, protects Patrick by throwing SpongeBob. Patrick suggests that they go inside to "play," but Sam explains how the house is too small. Sam then takes a briefcase filled with sand and constructs a new house, made of sand. Patrick thanks her. However, Squidward complains that his house is filled with sand. Again, Sam feels overprotective and moves Squidward's house with only her bare hands. Squidward makes jokes about Sam saying, how she is bigger, and dumber than Patrick. Sam responds by getting angry and then starting to cry because she already knows it is all true. Her giant tears throw both Squidward and SpongeBob.
After that, Patrick becomes overprotective of Sam by saying that SpongeBob and Squidward are "meanies" and saying that they should blecorate (decorate) the rock. However, she uses parts of Squidward's house to decorate it, damaging it greatly. Then Squidward gets angry and calls her a thief. Then SpongeBob tries to talk some sense into Patrick, but Patrick does not care that Sam deliberately dismantled Squidward's house. Then he starts crying, thinking SpongeBob has become a traitor and gets head-butted by Sam along with Squidward back to their houses, damaging his house further. Squidward gets angry and drops a rock on the house, ruining the "spiffy". In response, Sam and Patrick come out of the house and Sam chews up the loose parts and spits them at Squidward's house, completely destroying it.
In the last act of retaliation, Squidward then drives a bulldozer at Patrick, Sam, and the house, making Patrick and Sam realize that Squidward is literally going to kill them. SpongeBob tries to stop him but to no avail. Sam, who throws the bulldozer at SpongeBob's house, stops Squidward (whom suddenly disappears for the rest of the episode). After that, SpongeBob finally becomes upset at the destruction of his house, making Patrick finally see what SpongeBob means. Patrick tries to tell her to control her temper, but she gets very angry and destroys her own home while Patrick sacrifices himself to save the house. Patrick lays there unconscious but SpongeBob successfully wakes him up by using cookie dough. Sam feels very guilty and explains that she must leave (She is late for a manicure and shows them her nails). As Sam leaves on the bus, SpongeBob and Patrick laugh about their experience with Patrick's sister.
It is revealed in this episode that Patrick has an older sister.
In "Something Smells," Patrick stated, "I don't have a sister." It is possible he wanted to keep it a secret, or he forgot. As mentioned by Patrick in this episode, his sister was lost a long time ago, so nobody knew about her.
In the episode "Rule of Dumb," Sam should have been the so-called "Queen" of Bikini Bottom since she is older than Patrick, though, she didn't appear anywhere on the royal chart. This might possibly prove that Sam was forgotten since it was mentioned that they were split apart.
This is the third time Patrick appears cleaning his residence. The first would be "I'm with Stupid." The second time would be in "No Nose Knows." This time, he feels more eager and more prepared to meet a family member.
Running Gag: Sam crushes Patrick and pronounces "brother" as "brubber."
While Sam is spinning the tractor, you see the back of her head does not have a face. However, later, it does. She must have grown it in a similar manner that Patrick made a face on his back in "Survival of the Idiots."
Although there are many episodes where Patrick is constantly annoying to Squidward, this is the first episode where Patrick had a bitter rivalry toward him due to caring for his sister.
Squidward disappears for the rest of the episode after the bulldozer destroys SpongeBob’s house. It's mostly that he just gave up on competing with Sam.
Sam may be a reference to the Incredible Hulk because of her exceeding strength and speech problems.
Sam's two faces are a reference to Lord Voldemort in Harry Potter and the Sorcerer's/Philosopher's Stone. It is also a reference to how recent LEGO minifigures having double sided heads often showing different expressions.
At some point during this episode, SpongeBob is a darker shade of yellow.
The first time that Sam pushes Squidward's house away, SpongeBob's house does not appear.
When Sam "spiffs" up the house, she adds the front door from Squidward's house. The doorknob is on the right, but in a few scenes later, it is on the left.
Sam pushed Squidward's house towards the right, closer to SpongeBob's house, and it didn't seem to go very far. Later, it seemed as though Squidward's house was pushed backward, and was pushed very far back.
In the first scene, Gary is much larger than usual. In the same scene, Patrick's house is seen to be much smaller; both Patrick and SpongeBob are taller than it. Later, in the scene when Sam arrives, the house is much larger. Throughout the episode, Sam also changes size.
During the episode, Sam has no nails, but at the end of the episode, she says that she has to go because she's late for manicure.