"Trilogy of Error" is the eighteenth episode of Season 12. It aired on April 29, 2001. The episode was written by Matt Selman and directed by Mike B. Anderson. Frankie Muniz and Joe Mantegna guest star. This episode features many connections in the 3 stories. For example, at the end of Homer's story, he witnesses Linguo fall into a trash can from and explosion, and it is explained in Bart's story where they have to sacrifice it.
Homer's thumb is cut off following breakfast and the episode follows three different paths. Homer's day; as he and Marge race to get his thumb reattached. Lisa's day; as she misses the bus and tries to get to school so that she can win the science fair. Bart's day; as he and Milhouse make use of a stash of fireworks that Fat Tony has illegally smuggled into the country. In the end their respective paths come together.
Homer is getting ready for work and after coming out of the shower he tries to eat breakfast. However, Marge bought a really hard to eat breakfast from Europe. Bart leaves when Milhouse rings the doorbell. Lisa tries to spare her mother's feelings by winking to Homer and asking if he wants to see her school project, Homer not understanding what Lisa is doing says no but he'd rather do that than eat the crappy breakfast, leaving Marge in the kitchen hurt. Lisa shows Homer her science project, Linguo, a grammar fixing robot. When Homer says "Me love beer," Linguo corrects it by saying "I love beer." Because Homer is stupid, he misinterprets into thinking that Linguo loves beer, so he grabs a can of Duff for Linguo. It causes it to malfunction. Homer then sees a tray of brownies and wants one but Marge does not allow it. Homer tries to grab the brownie without her noticing, but while she is cutting some food, she accidentally cuts off Homer's thumb. Marge tries to call 911, however Chief Wiggum, who picks up the line misinterprets the information as a deliberate attack and states that she will be arrested, forcing Marge to use a fake address of 123 Fake Street. Marge drives Homer to a doctor, but crashes into Rainier Wolfcastle's car forcing them to carjack him. After learning from Dr. Hibbert that Homer's finger insurance does not cover his thumb, Marge drives Homer to Dr. Nick's. Homer's thumb starts to decay, so they make a pitstop at Moe's Tavern and Moe gives Homer a new jar to put his thumb in to preserve it. After wasting time in the bar, Homer comes out and finds out that Marge and the car are gone. Homer catches a ride with Cletus to go to Dr. Nick's. However, it is on fire by an item that was supposed to be inflammable and Cletus's truck is stolen, forcing Homer to walk to Shelbyville. On the way he sees Linguo's head in the trash following an explosion.
After Homer causes Linguo to malfunction, Lisa goes to her room and repairs it. But when she has to leave, her bike is missing, the bus has left, and Homer and Marge have left for the hospital. Lisa runs to school and sees Krusty's limo after it almost hits her. Krusty has his chauffeur Mr. Teeny take Lisa to school, passing Chief Wiggum along the way who asks for directions to 123 Fake Street. However, Mr. Teeny thinks that Lisa is supposed to go to West Springfield Elementary School. There, she meets a student named Thelonius, who she falls in love with. Lisa then runs to Moe's Tavern to find Homer, but he's is not there. She notices that Chief Wiggum is working on a sting operation to catch some fireworks smugglers and is listening to the conversation with some people he sent undercover and the criminals. When Lisa recognizes one of the criminals as Fat Tony, Wiggum speaks into the microphone which exposes his undercover people. Just as Lisa leaves Moe's, Homer and Marge arrive and she sees Marge outside. Lisa hops in her car which Marge stole from Rainier Wolfcastle and leaves when Marge hears Homer talking to Moe drunk and knows she has plenty of time to drive Lisa to school. However, the car instructions are in Italian and they run out of fuel. Marge and Lisa then take a ride in Cletus's truck by hiding in the back and after arriving at Dr. Nick's, Marge steals the truck during the time that Homer and Cletus observe that the hospital is on fire. With only a few minutes of school left, they nearly run over Bart and Milhouse.
Milhouse comes over and Bart tags along with him. They steal Lisa's bike and go to a cave where Milhouse has found firecrackers. They then proceed to blow stuff up including Dr. Nick's (where the firework hit the inflammable item) office until they hear sirens and hide in an abandoned building called 123 Fake Street. They are caught by Chief Wiggum. The boys are then put into a sting operation to find the real firework smugglers, which is the Springfield Mafia. Bart and Milhouse are exposed when Wiggum speaks into their receiver and are forced to escape. They come out through a sewer and exit through a Manhole cover. They are nearly run over by Marge and Lisa. The boys, Marge, and Lisa are then confronted by Fat Tony in an alley, but Lisa has to sacrifice Linguo by having him fix the terrible grammar of Legs and Louie. It causes Linguo to explodes due to the sparks igniting Fat Tony's fireworks which also takes down the mobsters. Linguo head then falls into the trash where Homer finds it. Marge finds out that both Bart and Milhouse were hiding in a trash can.
Legs is able to reattach Homer's thumb with success and it becomes Lisa's science project. It wins first place. Then the whole episode cast comes and laughs except for Mr. Teeny who murmurs "this plot made no sense." Which is an example of "breaking the fourth wall".