Lisa falls for the teenaged leader of a militant environmentalist group and tries to impress him by living in Springfield's oldest tree in order to keep it from being cut down.

Homer decides to buy a computer after turning up to the Plant to find it closed by e-mail. He then creates his own website and it eventually gains attention when he posts gossip. Homer dubs himself as "Mr. X" to conceal his identity. When he reveals that he is Mr. X, he becomes drugged into a mysterious island where people who know too much are imprisoned after Homer starts writing conspiracy theories such as flu shots.

Homer and Bart become father–son con artists (after Bart is given money out of pity when Homer decided to not take him home), but soon find that they are the ones being had.

When the Simpsons once again have financial problems, Mr. Burns pays Homer to play pranks on others and humiliate himself in public. Meanwhile, Smithers creates a Malibu Stacy-themed musical.

Marge tries to rehabilitate a convict with remarkable artistic talent. Meanwhile, Homer uses a trash can to fix people's spines.

A snowstorm traps the students of Springfield Elementary inside, with them overthrowing Principal Skinner when he uses his Army skills to control them. Meanwhile, Homer tries to rescue the children–using Flanders' car.

While making funeral arrangements for Grampa's future, the funeral planner pitches the idea of a mausoleum that uses the same amount of cement as a full-sized tennis court. This prompts Homer to instead build a tennis court in his backyard, initially mistaking the sport for "Foxy Boxing". The tennis court makes Marge and Homer popular in town, but it turns out that this is only because Homer's inferior tennis ability makes them an easy target. Bart on the other hand, shines as a natural.

Bart and Milhouse are banned from The Android Dungeon after stopping Comic Book Guy from buying a box of priceless Star Wars memorabilia for $5, but are hired as his replacements when Comic Book Guy has a heart attack and is advised to leave his job in order to make friends.

Homer becomes a Good Samaritan after discovering the simple joys of helping people in need–which is put to the test when he goes on a hunger strike after the owner of the Springfield Isotopes attempts to discredit him when Homer stumbles on his plot to discreetly move the team to Albuquerque, New Mexico.

Krusty announces his retirement due to interference from network executives and the growing popularity of the big-money game show "Me Wantee", but when Krusty reveals to Sideshow Bob that all of the episodes featuring him have been erased, Sideshow Bob uses Krusty's biggest fan (Bart) to murder him during Krusty's farewell show.

When Lisa becomes the target of a female bully, Lisa discovers a scientific reason as to why bullies pick on nerds. Meanwhile, Homer goes into the baby-proofing business, which is threatening the businesses of pediatricians and greeting card salesmen.

A music producer selects Bart, Nelson, Milhouse and Ralph to be members of the next hit boy band, who record subliminal songs about joining the Navy.

When the Simpsons run out of food thanks to a bag boy strike (caused by Homer), the family finds an old box of animal crackers with a sweepstakes that sends The Simpsons to Africa.

Homer's rush to the hospital to reattach his thumb, Lisa's rush to school to win the science fair, and Bart's run-in with an illegal fireworks scheme are interconnected in a parody of Go and Run Lola Run.

After finding a sketchbook belonging to his late wife Maude, Ned Flanders opens a Bible-themed amusement park to honor her memory.

After spraining his knee during a basketball game, Homer begins taking care of the neighborhood kids to cure his boredom, prompting jealousy from Bart and Lisa, who feel that Homer is giving the kids the attention they never had.

When Homer refuses to pay a five dollar airport tax to fly to Delaware, the family is forced to ride in a livestock car of a train instead. There they meet a singing hobo who tells three tall tales: Homer as Paul Bunyan. Lisa as Connie Appleseed, a parody of Johnny Appleseed. Bart as Tom Sawyer with Nelson as Huckleberry Finn.

Homer becomes a fortune cookie writer for a Chinatown restaurant. Mr. Burns reads one of Homer's fortunes, which says that the reader will find love before Flag Day is over. Burns goes searching for love and meets Gloria, a meter maid, and asks her out. Gloria reluctantly agrees, and Burns recruits Homer to help him look young and hip to his new girlfriend.

In the twelfth Treehouse of Horror episode:

Hex and the City – While on a day trip through Ethnictown, Homer's bumbling catches the ire of a gypsy, who curses Homer's family and friends into receiving nothing but bad luck.

House of Whacks – in this mixed parody of Demon Seed and 2001: A Space Odyssey, Marge buys an automated house and customizes it with the Pierce Brosnan personality, who falls for Marge and attempts to murder Homer.

Wiz Kids – In this Harry Potter parody, Bart and Lisa go to a school for wizards, and Lord Montemort (Mr. Burns) uses Bart to capture Lisa's magic.

Guest star: Pierce Brosnan and Matthew Perry.[20]

Moe becomes depressed and decides to return to bartending school so he can re-evaluate himself. He meets an old teacher, who suggests that Moe try improving his bar, which might make him happier. Moe takes the advice, and turns his bar into a trendy nightclub, which does not sit well with his regular customers Homer, Lenny, Carl, and Barney.

After tricking Marge into thinking an advertising spokesman is coming to visit her, Homer takes Marge and the rest of the family to a restaurant. A hypnotist uses his powers on Homer, and makes him remember a horrific childhood incident where Homer found a dead body in a ravine. The Simpson family decides to investigate this and find out where the body came from.

Bart gets in trouble for joyriding in a police car, but feels confident he will be let off by Judge Snyder. However, Snyder goes on vacation before ruling his verdict and is replaced with a coldhearted judge named Constance Harm. She accuses Homer of being a negligent father and sentences him to be tethered to Bart. The two are against it at first but later start to bond. Marge however is unable to take anymore of it and slices the tether off of them both. Homer and Marge then go after Judge Harm only to end up sinking her houseboat. Eventually Bart decides to take punishment and is about to be sentenced to 5 year in juvenile hall, only though Judge Snyder returns and dismisses Harm.

Guest star: Jane Kaczmarek and Jess Harnell.[21]