"Please Homer, Don't Hammer 'Em" is the third episode of Season 18.
Marge gets a job as a carpenter, but every man in town thinks she is going to ruin everything she fixes because Marge is a woman, so Homer pretends to be the carpenter while Marge does all the work, until he starts receiving too much credit for doing nothing.
On a trip to an extremely poor mall, Homer happens across the Time Life Carpenter’s Library, and Marge encourages him to buy them. Also seen is 'I, Scoundrel' by Esme Delacroix, a book featured in a previous episode. Homer's interest in carpentry fades, and Marge plans to use them herself to fix up the house, starting with her broken nightstand. She begins to learn more and more about carpentry and Lisa suggests to Marge that she try to earn some money as a handyman, thus opening up 'Simpsons Carpentry'. However, potential clients (Superintendent Chalmers and Krusty the Clown) turn her down, dismissing the idea of a woman carpenter. Commenting on how people expect carpenters to be big fat guys "with their butt cheeks showing", Marge develops a plan. She uses Homer as a front to the customers, while Marge, hiding in an accompanied red tool chest, does the all of the work as Homer rests in the tool box. Starting on Professor Frink, she finds this plan as a success.
Meanwhile, a note is sent out from the school, informing parents that someone at the school has a peanut allergy so peanuts will no longer be allowed on school premises. An indignant Bart claims it to be unfair to disclose the identity of the "kid," but he soon discovers the "kid" is actually Principal Skinner. With this newfound knowledge, and with the assistance of a peanut on a yardstick, Bart is able to abuse Skinner by making him do a number of humiliating activities, such as firing tennis balls and cola cans at him, making him eat garbage in bed and making him read a "cootie" poem over the tannoy to the whole school.
While business is going great, Marge becomes a bit discouraged by Helen Lovejoy and Lindsay Naegle when she is out buying supplies at Builders' Barn, who berate her for being Homer's "helper" ("Hey Marge, I think you broke something. Better call Homer!"). That night, Marge tells Homer that he feels he's taking too much credit (his shirt now has 'I do all the work' printed on it) and wishes she would get some recognition for the work. Homer, however, doesn't want to be humiliated by revealing his wife did everything. After an incident in which Homer mocks Marge's carpentry skills with Lenny and Carl, who then kick the toolbox she is hiding in to the tune of We Will Rock You, Marge becomes enraged and quits, leaving Homer alone to do his biggest commission yet: repairing Springfield’s old wooden roller coaster, "The Zoominator". Homer tries to fake his way through being a foreman in front of his newly hired construction crew, but they eventually abandon him when he reveals he can't pay them via sobbing and screaming in the box.
Meanwhile, Skinner eventually realizes he could exploit a weakness of Bart's, and searching through medical records of one Bart Simpson, finds exactly what he's looking for: something Bart's allergic to. The next day, Skinner counters Bart's peanut stick with his own: a shrimp on a stick.The two Bart and Skinner clash with their respective “sticks”. Taking them across town and on top of a bus roof, eventually leading them into into a Thai Food Factory in the "Little Bangkok" section of town. They battle over a rickety catwalk, until it gives way, plunging them both into a vat of peanut shrimp, setting off both of their sensitive allergies. Also, Bart reveals that he was El Barto, causing Skinner to shout "Noooooo!"
The big reopening day arrives, and Homer stands in front of a crowd, gathered to witness the unveiling of the refurbished roller coaster. Marge has a video camera at the ready, so she can catch Homer being exposed as a fraud on tape. When revealed, the crowd is in awe at the seemingly repaired roller coaster, but with a hit from Homer's popped cork from his champagne, the coaster dilapidates, becoming as rundown as it previously was. Still not wanting to admit the truth, Homer proves the coaster is safe by riding it himself, even though there are large gaps in the track. Acting quick, Marge is able to repair each broken piece just before Homer's cart runs over it. While riding, Homer announces to the crowd that Marge did all the handy work. The crowd applauds as the coaster comes to a stop at the beginning, and just as Marge is about to tell Homer that she loves him, the entire roller coaster structure comes crashing down on top of him. At the hospital, Marge visits Homer, who is okay but immobilized in a full body cast, tells him she loves him and to get well. Bart and Skinner rest in their respective hospital beds in the same room as Homer, and the two proceed to throw shrimp and peanuts at each other to set off their respective allergies once more. Marge plans to go and see the new babies. She walks to the maternity ward as the episode finishes. (Marge is under the impression that Bart jumped into the peanut shrimp vat to save Principal Skinner.)