Marge, with a little help from Patty, Selma, and Jack (Daniels), e-mails Artie Ziff, who offers $1,000,000 for a weekend ("no funny business") alone with her - money they could use for an operation to make Homer stop snoring.
Marge is irritated when Homer is snoring, causing her to become sleepless. She sees Dr. Hibbert about the problem, and asks about surgery, but he says it is expensive and tells them to get out when Homer asks him to do it for free. Developing a sleep problem, she spends a night at Patty and Selma's apartment, and hears on the news that her old boyfriend, Artie Ziff, is one of America's five richest people. She dictates an e-mail to Artie to congratulate him on his appearance, but Patty and Selma doctor it to use sexual terms in an attempt to split up Marge and Homer, much to Marge's horror (for using the word "sex" on the Internet). Artie receives the email and turns around in his chair claiming that he was "just thinking about Marge" and then adds "For the last thirty years!". It is then revealed that he never exactly got over the events that happened on the night of their high school prom (where he ruined their date with his perverted desires and Marge walked out on him and began a relationship with Homer instead) and has seemingly developed an unhealthy and rather frightening obsession with Marge as his house is decorated with a large number of Marge sculptures/paintings and other pieces of furniture that have had her face crafted onto it. He then flies in his helicopter to the Simpson house to see Marge.
After arriving, Artie offers Marge a $1 million proposal to spend a weekend with him, just to see what life would be like if they were married. Marge initially rejects the offer, but eventually can no longer stand it as Homer's condition has advanced to the point that he actually snores while awake. She chooses to spend the weekend so she can get the money for the surgery. They have a good time until Artie tricks Marge into making out with him against her will in a reenactment of their prom during the 70's made to mirror of the one they attended in "The Way We Was" (with even its original attendants who were paid by Artie to show up disguised as they were at that time). Homer, having anxiously arrived to check up on them, sees them kissing and, unaware of the true premises, is devastated, and leaves Springfield with Lenny.
Lenny seems similarly dejected about his relationship with Carl; he and Homer get a job in an oil field in West Springfield, a likely death spot for the two of them. On the way there, they discuss the loves they left behind. Homer was so heartbroken, that a lot of cacti resemble Marge to Homer, and Lenny mournfully points out Mount Carlmore that he carved one blissful summer. Meanwhile, Marge leaves Artie furiously, only to discover what Homer has done when she gets home and finds out he is not there and that he has left a tape behind featuring his withdraw (and strangling Bart during recording), leaving Marge overwhelmed.
While working on an oil rig, Lenny and Homer accidentally set fire to an ant, who in turn sets fire to all its ant companions, who jump in a puddle of oil to dowse the flames. Their brief sighs of relief are replaced with screams as the whole rig catches fire. Marge, Bart, and Lisa go with Artie and Carl to West Springfield to save Homer and Lenny. At first, they are reluctant, as Homer still thinks that Marge and Artie are having an affair, and Lenny feels that there is nothing for him in Artie's helicopter. However, Artie finally admits defeat to Homer, saying that winning Marge's love was something that he could never accomplish, even with his billions, and Homer jumps on the ladder to the helicopter. Carl reveals that he is in the helicopter, and Lenny also jumps on to be saved, just before the rig collapses. Homer and Marge's marriage is also apparently saved when Artie offers a solution to Homer's snoring problem, a device which converts snoring to music and anti-Homer subliminal messages (although Artie seems to reveal himself soon after the messages start).
In its original broadcast, the episode was seen by approximately 7.5 million viewers and finished in 36th place in the ratings the week it aired. Since its original broadcast, "Half-Decent Proposal" has received mostly positive reviews from critics, some of whom considered it among the best episodes of the season.
However, the episode has also been criticized for parodying Indecent Proposal nine years after its release, a criticism which the episode's showrunner Al Jean responded to in the episode's DVD commentary.