Selma realizes, after going to the wedding of a man that could have easily been hers if Patty had not intervened, that she needs to find a husband and begs Marge to help her. Marge enlists the help of Homer to seek one out; however, Homer has trouble finding anyone suitable. Meanwhile, Bart pulls a big prank by pouring the fictional herbicide sodium tetrasulfate onto the grass of his school, spelling out his own name, and is caught when Skinner sees the mess. Homer meets with Principal Skinner about Bart's behavior and, learning that Skinner is single, invites him home to dinner with Selma. Later that day, Skinner arrives for dinner, but instead of falling for Selma, he becomes instantly smitten with her sister, Patty after she yells at Homer for being the wrong twin.
Skinner asks an unwilling Patty out on a date and she tries to get out of it by refusing. However, as they are going home, Selma tells her that she needs to go on this date because she has not been with a man in 25 years and this would be her best chance to still have a family. On their first date, Patty does not seem impressed with Skinner until he yells at his former student for his lack of promptness. Soon after they go out on more dates, much to Selma's chagrin and she realizes another decent man has just slipped past her.
Skinner enlists Bart's help to get Patty to marry him, while Homer fixes a date between Selma and Barney, which Selma reluctantly accepts. However, Marge disapproves of Barney and demands Homer to find someone else suitable for her sister. Skinner takes Patty to the top of the bell tower to propose. Following Bart's lead, he has written "Marry Me, Patty" in 40-foot letters using the sodium tetrasulfate that got Bart in trouble. Patty is flattered, but declines. She admits to Skinner that she shares a common bond with the emotional grief of her twin sister, which Skinner immediately understands. Patty appreciates Skinner's understanding and his gentlemanly conduct, and if she ever did settle down with a man, she would want it to be with him. Rescuing Selma from her date with Barney, Patty takes her home.
Meanwhile Skinner, who vows to win back his school from Bart's control (who was taking advantage of the fact that Skinner loves Patty and turned a blind eye from all of Bart's recent vandalism), destroys all the grass on the school field with the sodium tetrasulfate, forcing Bart to replant the field seed by seed, much to Groundskeeper Willie's pleasure.