Homer is relaxing on a Saturday when Marge tells him that he should be doing work around the house and yard. Homer overcomes his reluctance and takes Bart to Mom & Pop Hardware to get some equipment. But while there, Homer sees a do it yourself barbecue pit and is compelled to buy it instead of anything that might help him with his work. Homer tries to install the pit, but bungles the job when he drops the parts of the barbecue into wet cement. He frantically tries to assemble the barbecue pit before the cement hardens, but only makes things worse. In the end, Homer is left with a mismatched collection of parts stuck in hardened cement, which angers him. He vents his rage on the construct, mangling it further. Later, Homer takes the results of his work back to the store for a refund, which he does not receive. On the way home, Homer loses control of the wagon containing the jumbled mess of concrete and bricks. It rolls down the highway and crashes into a woman's car, wrecking it. Homer flees the scene of the accident, but the woman tracks him down. It turns out that she is an artist named Astrid Weller (voiced by Isabella Rossellini), and sees Homer's handiwork as being a masterpiece of outsider art. Homer's exhibit goes to the Louvre: American Style museum and when Mr. Burns buys his work, Homer becomes a success.
Now officially an outsider artist, Homer uses his channeled rage to continue his work and befriends other stereotypically pretentious artists, like Jasper Johns. All the while, his easily achieved fame makes Marge jealous due to her lack of success at becoming a successful artist despite years of effort. Homer later gets a notice from Astrid Weller that his work will be in the "Art in America" show, but his new masterpieces are rejected by Springfield's residents and his new "friends" for being repetitive of his first piece.
Down on his luck and starved for inspiration, Lisa recommends Homer visit the Springfield Art Museum. But none of the art Homer sees serves to inspire him; he feels inadequate when he sees what other artists have done, and it only worsens the situation when he takes a nap and has a nightmare of various paintings attacking him. He goes back home, discouraged, but is soon given another suggestion by Lisa. She tells him about the artist Christo, causing Homer to try doing something similarly groundbreaking. He and Bart flood Springfield by opening all the fire hydrants (having covered the sewer drains with the city's doormats, including their own) and putting snorkels in the animals of the zoo (so that they do not drown). Surprisingly, Astrid Weller and even the whole town of Springfield is impressed with Homer's work, and enjoy the newly made "Grand Canals of Springfield" along with the swimming zoo animals. As Marge and Homer kiss each other on the roof of their house Jasper Johns comes on a boat and steals the painting Marge was painting. The song playing in the end of episode is "Arrivederci Roma" performed by Michael Dees.