The Chamber of Commerce Dance is coming up, and Barney is going with Thelma Lou...at least, he thought he was. Thelma Lou tells him that her cousin, Mary Grace is coming, and Thelma would like her to have a date. Barney is appalled, remembering Mary Grace. He compares her with a dog, and Thelma Lou is offended, telling Barney that she won't go to the dance with him unless he finds a date for Mary Grace.
Barney tells his troubles to Andy at the courthouse, even asking if Andy would go out with her. But as they talk, Gomer Pyle walks in. Barney realizes that he has found the perfect match. He and Andy tell Gomer about Mary Grace...except whenever Gomer asks, "Is she pretty?" Barney and Andy avoid the question.
Thelma Lous is uncertain about whether Gomer is a good choice, but finally agrees. So she and Andy's date tell Mary Grace about Gomer, although the conversation is similar to what Barney, Andy, and Gomer had earlier.
The three men arrive at Thelma Lou's slightly late, as Aunt Bee was determined to straighten Andy's pants out, claiming that they were baggy. Andy's date, and Thelma Lou are given corsages. The men are invited inside, and Mary Grace enters. Gomer seems to like her, but after at least five minutes, says that he's got to go do something, and leaves.
Mary Grace is slightly disappointed, and says that she'll just read or something, and tells the others to go to the dance. They do, but the ladies, especially Thelma Lou, are reluctant. In fact, when Barney tries to hit on Thelma Lou in the backseat of the squad car, she punches him, and he immediately holds a cloth to his nose. (It isn't clear as to whether his nose was actually bleeding or not)
After they leave, Mary Grace curls up on the couch to read a book. But there's a knock on the door, and Gomer enters. He apologizes, because when he saw that the other ladies had corsages, and Mary Grace did not, he felt like he needed to get one for her, and he didn't mean for it to take so long.
At the dance, the four arrive. Thelma refuses to get out of the car, saying that she has a 'headache'. Andy's date says that she'd better stay with Thelma, and finally the men decide to leave. When they come back home, they can hear music playing loudly from the inside. Gomer and Mary Grace are dancing. (Gomer very energetically)
At the end, they are all talking and laughing...although Gomer seems to not be able to stop telling stories...