Lisa pressures Homer into buying her a guinea pig, whom she names Pokey, but no sooner has she brought her new pet home than Pokey escapes and gets into the living room wall, tearing a hole in the iconic sailboat painting while tunnelling out again. Heartbroken over the loss of the painting, Marge suggests she and Homer get a replacement from an art gallery, but he decides to go the cheaper route by going to Kirk and Luann Van Houten's yard sale, where he buys a seascape that used to hang in Kirk's bachelor apartment for $20.
However, when Marge removes the ugly chrome frame, they see a signature: Johan Oldenveldt, a late 19th/early 20th century Dutch naturalist whose paintings sell for thousands at auction. The Simpsons have the painting appraised and are told it could fetch $80,000-$100,000. Homer discourages Marge from telling the Van Houtens about the painting's value so that they can keep the money for themselves, but Milhouse overhears their conversation and, despite ample bribery from Homer, is unable to keep the secret from his parents, who are furious that the Simpsons were not planning to share the money. Word spreads, and the town splits into two factions, one siding with Homer and Marge and the other with Kirk and Luann. The initial bid at the auction is $80,000, and there is plenty of interest, but proceeds grind to a halt when Dawn, a woman with whom Kirk had a brief relationship while separated from Luann, shows up and insists the painting is hers. Outraged that Kirk never told her about Dawn, Luann throws him out.
Kirk tells Homer that he paid for the painting and that Dawn is an Attention Whore who joined him on a trip to an artist's community on nearby Isla Verde, only to leave him for a parasailing instructor immediately after he bought the Oldenveldt. Homer takes Lisa to Isla Verde (even though Marge, upset over the strife the painting has caused, insists he let the matter drop), and the proprietor of the cafe where Kirk bought the painting confirms his story. Homer's joy is short-lived as a cafe patron, Klaus Ziegler, reveals that he painted the Oldenveldt; he is a professional art forger who has fooled galleries and auction houses the world over. Lisa is initially outraged, but concedes that if his paintings move people, there's no harm in that. Homer proceeds to commission three paintings from Ziegler: a copy of a jukebox poster he wanted to buy at the yard sale, a Van Houten family portrait that helps Kirk and Luann reconcile, and a replacement for the sailboat painting.
- Armor-Piercing Response: When Lisa objects to Klaus forging famous art, Klaus points out that Lisa only cared about the painting when she thought someone famous painted it. Which Lisa can't deny.Lisa: What you do is horrible! Ripping off geniuses who spent years perfecting their styles!
Ziegler: Perhaps you are the one who is horrible.
Lisa: [outraged] Whaaa?!
Ziegler: You only cared about that painting when you thought it was created by someone famous.
Lisa: [stammering] Well - no - but - now, when I look at it, all I see is a fraud.
Ziegler: Beauty is beauty. [cut to various people admiring Ziegler's paintings, including Ralph Wiggum in an art gallery, Richard Branson in a space capsule, a dictator in his bedroom with a lion, and two security guards watching over the fake Oldenveldt who exchange an adoring look before joining hands] My forgeries give pleasure to people all over the world. The only real question to ask about art, whether it's in the Louvre or on a freshman's wall at Cal State Fullerton is, "Did it move you?"
Lisa: But - you still - I mean - oh, I suppose you're right.
Homer: What if I never liked the painting and only wanted it for money?
Ziegler: Then you, I respect.
Lisa: [furious] UGHHH!
- Book Dumb: When Marge suggests giving the Van Houtens 25% of the money, Homer says they'll be mad about the 65% they're keeping.
- Brick Joke: While looking for a new painting to replace the one destroyed by Lisa's new guinea pig, Homer shows interest on a loud jukebox picture. At the end of the episode, Homer gets, besides a new ship painting to replace the destroyed one and a family portrait to help the Van Houtens to reconcile, a copy of the jukebox one.
- Cannot Keep a Secret: When Milhouse overhears Homer and Marge agree not to tell Kirk and Luann about the painting being very valuable, Homer buys his silence with a spending spree at Toys B This (and then has to buy off Lisa for saying she's in love with Milhouse, and Bart to get him to agree to use Milhouse's new nickname of C.J.). The very next day, an irate Kirk and Luann and a sheepish Milhouse show up on the Simpsons' doorstep, with the adult Van Houtens furious that the Simpsons were planning to keep the painting's value a secret from them.
- Death Glare: Kirk and Luann have venomous expressions whenever they make eye contact with Homer and Marge after Milhouse confesses that the painting they sold for $20 at a yard sale might fetch $100,000 at auction, but the Simpsons weren't even planning to tell the Van Houtens, much less share the money with them.
- Freeze-Frame Bonus: The Artipidea article on Johan Oldenveldt is a goldmine of hilarity - Oldenveldt's main inspirations were a dispute with his landlord and losing a fortune after a bad investment in whaling ships, and his work is divided into three periods (Arsenic, Sulfur, Mercury) based on the treatments he was undergoing for venereal disease (which ultimately caused his nose to fall off) - but it's only on screen for a few frames.
- Gargle Blaster: Strupo, aka "Angel's Urine", is Isla Verde's local drink made from fermented capers. According to the promotional video at the end of the episode, its original use was to dissolve seagull corpses, and its side effects include "olfactory hallucinations, gender confusion and wandering mouth."
- Misplaced Retribution: The auction is interrupted when a woman who used to date Kirk back when he and his wife were divorced is claiming ownership. Luann is angry because Kirk never told her about that woman. Marge is upset at Homer because she blames his obsession with the painting for the new threat to the Van Houtens' marriage. Not only could Homer not reasonably expect this outcome, but Kirk bears more blame for hiding it from his wife.
- The Reveal: The painting is revealed to be the work of someone who copied Johan Oldenveldt's style and signature instead of a work of Oldenveldt himself.
- Series Continuity Error: Lisa claims she's never had a pet of her own, but she's had two cats and a hamster.
- The Unfair Sex: Luann is mad at Kirk for seeing people whilst they were separated, despite having plenty of boyfriends in that period. That said, she could have just been more mad that he lied about it, but it's still pretty hypocritical.