Homer finds himself filling in for the Springfield Nuclear Power Plant's union leader when it comes time to negotiate their new contract with Mr. Burns. Homer is a tough negotiator, despite not knowing the first thing about union organizing, and forces Burns to accept the union's demands on the condition that Homer be removed as leader.
Mr. Burns sits in his office awaiting the union leader, who hasn't been seen since he promised to clean up the union (it's implied that he was killed in the effort), so that they can discuss the proposed union contract. Overlooking the contract, Mr. Burns is disgusted with the demands and reminisces about simpler times. As such, Mr. Burns decides to take on the greedy union and revoke their dental plan.
Meanwhile, at Painless Dentistry, the Simpson children are getting their teeth checked. It is discovered Lisa needs braces. When Marge informs Homer, he tells her not to worry about the cost, as the union had won a dental plan during the strike of 1988. Later, at a meeting of the local chapter of International Brotherhood of Jazz Dancers, Pastry Chefs and Nuclear Technicians, Carl announces that the newest contract requires the union to give up their dental plan in exchange for a free keg of beer for their meeting. Homer slowly comprehends that giving up their dental plan would require him to pay for Lisa's braces and jumps into action, reminding everyone how their dental plan has helped them all, and how the new contract is an insult. Carl proposes Homer be the new union president and is promptly elected by a nearly unanimous vote.
Mr. Burns monitors Homer and is impressed, confusing his attempt to get a candy bar off his back with exercising. Burns invites Homer to his office to try to reach an agreement but Mr. Burns' sly innuendos are mistaken by Homer as sexual advances. Homer quickly gets to his feet, saying he doesn't go for those "backdoor shenanigans" and promptly leaves.
Lisa is given her new braces, which are extremely noticeable, leading her to call herself a "monster". Meanwhile, Mr. Burns sends hired goons to Homer's in order to take him back to Burns Manor to negotiate and once they sit to talk, Homer begins to need to use a bathroom. He asks where the bathroom is and immediately leaves, causing Burns to think that Homer is unwilling to even hear him out. Homer finally becomes fed up with Mr. Burns and calls a meeting where the union immediately vote to strike.
Mr. Burns is undeterred by the strike and he tries several methods of breaking it up, such as bringing in 30's era strikebreakers and getting loyal robot workers. On an edition of Kent Brockman's talk show "Smartline", Mr. Burns is allowed an opening tirade and he threatens dire events. Fifteen minutes later, Mr. Burns and Smithers march to a secret room in the Power Plant and turn off the power for the whole town. The strikers don't lose hope and begin to sing. Burns, confident he has broken the union's spirit, steps out of his balcony to hear their reaction but is disarmed by their unity and optimism. Mr. Burns finally calls a meeting with Homer to concede to their demands on one condition: that Homer must resign as union president. Homer celebrates, causing Mr. Burns to finally realize that Homer is not a brilliant tactician.
With the Simpson family insured again, Lisa gets her perfect new braces and she, the Simpson family and the dentist gather and laugh as the episode comes to a close (as he had left the 'laughing gas' on).
The idea for this episode came from Mike Reiss, who thought it would be funny if the plant went on strike. The writers of the episode, Kogen and Woolodarsky, would later add the dental plan part. In several scenes, Mr. Burns is portrayed as the Devil who is tempting Homer and showing him what he could have. During the production of this episode, an ABC camera crew was allowed into the rewrite room, which Al Jean says he regrets because they were working on stage direction, and they came off as not being very funny.
The producers originally asked Anthony Hopkins and Clint Eastwood to provide the voice of the dentist, Dr. Wolfe, but they both turned it down. Anthony Perkins was later asked to fulfill the role and he agreed, but passed away before the role could be recorded. In the end, the role went to Simpsons regular Hank Azaria. Also, the original panelist on Smartline was supposed to be O.J. Simpson, but he turned it down, which the writers believe was a good thing.
This episode is generally ranked as being the best of all time and is on a number of Top 10 lists. An "Entertainment Weekly" article from January 2003 looking back at the top 25 episodes of the series chose this episode as the show's greatest episode, saying "this episode is virtually flawless, the product of a series at the height of its creative powers -- when the satire was savage and relevant" and "the stuff of syndication legend: Burns facing down brilliant labor kingpin Homer Simpson; Homer Simpson facing down his own brain (Lisa needs braces/DENTAL PLAN!); Grampa rattling on about wearing onions on his belt. Last Exit is a glorious symphony of the high and the low, of satirical shots at unions." In his book "Planet Simpson", Chris Turner (writer)|Chris Turner calls it the best episode of the series, saying "Episode 9F15 of The Simpsons should be taught in schools, in history, economics, social studies, literature and art class. It's flawless" and calling it "the funniest half-hour in TV history" He maintains that he chose the episode as best ever before EW's list was published. In 2003, to celebrate the show's 300th episode, USA Today published a top 10 chosen by the webmaster of The Simpsons Archive, which had this episode in first place. The BBC website says "This fine episode contains several of our favourite sequences ... A classic, and the series' most marked expedition into the surreal - up to this point." The episode earned an 8.9/10 on IMDB, and a 9.1/10 out on TV.com.
Director Mark Kirkland considers this episode to be one of the most surreal episodes that he has worked on because it has a lot of story crammed into it, lots of parodies and contains several visual sequences. Al Jean has also called this one of the craziest episodes. Homer's line "uh... Yeah" after being asked if he found the bathroom is one of Jay Kogen's favourite Simpsons jokes.