"Please Homer, Don't Hammer 'Em" is the third episode of Season 18.
When Marge gets a job as a carpenter, every man in Springfield fears she will ruin everything she fixes because of her being a woman. Homer pretends to be the carpenter while Marge does all the work, until he starts getting too much credit for doing nothing.
On a trip to the extremely poor mall, Homer happens across the Time Life Carpenter’s Library book collection, which Marge encourages him to buy. Homer's interest in carpentry fades, and Marge plans to use the books herself to fix up the house, starting with her broken nightstand. She learns more about carpentry, and Lisa suggests to her 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 as a carpenter. Dismayed with how people expect carpenters to be "big fat guys with their butt cheeks showing", Marge decides to use 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. After working with Professor Frink, she finds this plan to be a success.
Meanwhile, a note is sent out from the school, informing parents that peanuts are no longer allowed on school premises due to the discovery of a student with a peanut allergy. An indignant Bart claims it to be unfair to disclose the student's identity, but he soon discovers it is actually Principal Skinner. With this newfound knowledge and the assistance of a peanut on a yardstick, Bart torments Skinner by making him do a number of humiliating activities, such as firing tennis balls and soda cans at him, making him eat garbage in bed, and making him read a "cootie" poem over the tannoy to the entire school.
Despite her business being a success, Marge is somewhat discouraged when Helen Lovejoy and Lindsay Naegle berate her for being Homer's "helper". That night, Marge tells Homer that she feels he's taking too much credit (his shirt now has "I do all the work" written on it) and wishes she would get some recognition for the job. Homer, however, does not want to be humiliated by revealing that his wife does all the work. 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 quits in anger, 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, who eventually abandons him when he reveals he can't pay them as he sobs and bellows in the box.
Meanwhile, Skinner eventually realizes he can exploit a weakness Bart has, and searching through his medical records, finds something Bart is allergic to. The next day, Skinner counters Bart's peanut stick with a shrimp on a stick. 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 the pair 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 appears with a video camera, ready to 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 a popped cork from Homer's 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 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 in stable condition but is immobilized in a full body cast. Bart and Skinner rest in their respective hospital beds in the same room as Homer, and proceed to throw shrimp and peanuts at each other to set off their respective allergies once more. Marge plans to see the new babies in the maternity ward, under the impression that Bart jumped into the peanut shrimp vat to rescue Skinner.