This movie could be considered the pilot for the series. Stella Johnson is a single mother living in the town of Harper Valley. Now most of the townspeople, particularly on the PTA board, think that she is a little too liberal and liberated for them, so they are making things tough for her and her daughter. When the PTA board threaten to have her daughter expelled unless Stella changes her ways, she decides to get back at them by first exposing all their hidden secrets and then pulling all sorts of humiliating pranks on them. When she decides to run for the position of PTA President, they are really infuriated and try to stop her any way they can.
Because of a silly misunderstanding, Stella is booted off the annual carnival committee for Harper Valley High, but cooks up a plot with best friend Cassie to get even with the snobbish PTA members.
A misunderstanding leads the PTA members to believe that unmarried Stella is having a baby, and they set out to find her a husband to protect the reputation of their upstanding town.
Flora and the PTA members keep tabs on Stella by monitoring her mail, but Stella gets even by planting a phony letter from an imaginary middle eastern princess who just happens to be visiting Harper Valley.
After Wanda accuses Stella of trying to destroy her marriage, mother hen Flora hires an actor to romance Stella and break her heart.
Stella fakes amnesia to get the goods on Flora Reilly, who is involved in a corporate cover up that is illegally diverting water from Harper Creek.
Stella appears in a TV commercial for Kitchen Queen Paper Towels, unaware that she is working for her enemy, Flora Simpson Reilly who is the CEO of The Reilly Paper Company.
The Harper Valley PTA members accuse Stella of being an alcoholic when she is seen in town gathering beer cans. When Cassie (Fannie Flagg) refuses to throw Stella out of her hair salon, Flora (the town villain) tries to shut her shop down by setting up her snooty daughter Wanda in the beauty salon business.
Sentimental Stella chains herself to the oldest living tree in Harper Valley to save it from being bulldozed by Flora's workmen.
Stella picks up some extra shifts in the evening doing all the book-keeping for the local business people in town. But, the PTA members jump to the wrong conclusion and think that Stella is practicing the world's oldest profession when she is seen leaving the Harper Valley Motel late at night!
Flora Reilly thinks that Stella has inherited millions of dollars and promptly installs her as an honorary member of the Harper Valley PTA Board.
Mayor Harper approves an entertainment license for Kelley's Bar against town matriarch, Flora Reilly's advice. Angered by the mayor's actions, Flora tries to unseat the kindly Mayor Harper by backing her sleazy son-in-law (Bobby Taylor) in the up-coming mayoral election.
A bungling con man holds Stella, Cassie and all of the PTA board members hostage after a failed bank robbery attempt. When he realizes that he has wealthy Flora Simpson Reilly's daughter Wanda among the hostages, he demands 100,000 dollars and a 747 airliner to guarantee safe passage out of Harper Valley.
While taking diction lessons from the married English teacher at Harper Valley High, Stella becomes furious when she receives a sweater with a scarlet A on it from an anonymous member of the PTA board who assumes that she is having an affair!
After a three day health food convention in Cleveland, Stella and Dee arrive home to find Stella's Uncle Buster being arrested for causing an explosion on Harper Valley Drive with one of his latest screwball inventions. Annoying and intrusive at times, but after a heart to heart talk with her compassionate mom, daughter Dee learns to love Uncle Buster as much as Stella.
An angry and jealous Wanda throws Bobby out of the Reilly Mansion because of his casual flirtations, but then lives to regret it when he turns to her rival, Stella Johnson, for comfort and support.
At Stella's 25th High School Reunion, Calvin Kendall, an old boy friend of Cassie's, makes a play for Stella, causing the only fight that the two best friends have ever had. When Stella learns that Calvin is married she threatens to tell Mrs. Kendall about his cheating ways unless he repairs the damage and hurt feelings that he has caused her best gal pal Cassie.
Flora Reilly tries to shut down a local mens club, unaware that Mayor Harper and her son-in-law Bobby are members. After Stella gets busted for an illegal lottery ticket and thrown in jail, she discovers from public records that Flora's great grandmother founded the club and entertained men in a burlesque revue.
Stella gets a new job as Mayor Harper's assistant and a bribe from a shady man called Slick. He offers her $10,000 to steal copies of the construction bids for the new wing of Harper Valley's Hospital
After the Scrooge like CEO of Reilly Enterprises (Flora Reilly) refuses to sign the Holiday bonus checks for all her employees, she is knocked unconscious by a falling Christmas tree. Later, she is visited by three ghosts who show how her miserable life will end if she does not change her evil ways.
A destructive motorcycle gang called The Banditoes has arrived in Harper Valley. The gang's leader, Clutch Breath has informed town matriarch Flora Reilly that they have no intention of leaving unless Stella Johnson goes with them!
Flora Simpson Reilly writes a play for a community theater production and casts her daughter in the lead role of the Viking Princess. But, after Wanda falls and injures herself during a rehearsal, the director insists that Stella takes over the starring role in Flora's dramatic epic, "The Curse of the Widow's Heart".
When the town's fire department, run by Flora Reilly fails to respond to a local neighborhood blaze because of irresponsible volunteers and antiquated equipment, Stella demands that the town council elect a new fire chief. But, when Stella is elected to the position, Flora and her daughter Wanda do everything in their power to sabotage her efforts to improve the departments efficiency.
A doctors posthypnotic suggestion turns town meanie (Flora Simpson Reilly) into Stella's unlikely new best gal pal....temporarily, anyway!
The townspeople of Harper Valley think that Stella has flipped her wig when she becomes nasty and aggressively pursues a married man (Bobby Taylor) in a public restaurant. Stella has a hard time convincing everyone that her look-a-like cousin Della is actually the brazen hussy!
With the help of a charismatic union organizer named Kowalski (Sal Viscuso), Stella joins the picket lines to protest the unfair working conditions in Harper Valley which is run by the ruthless Flora Simpson Reilly.
Flora's rich cowboy nephew from Texas has agreed to give her millions of dollars to make improvements at the Reilly Paper Mill, with one condition. Cousin Claude is depressed about his love life and wants Aunt Flora to hook him up with that pretty little heifer, Stella Johnson!
Stella chaperone's Dee and her friends on a school related camping trip deep in the woods of Grizzly Gap. During a friendly poker game, Stella's Uncle Buster and Mayor Harper learn that a dangerous criminal has escaped from jail and is heading back to his old hide-out at Grizzly Gap.
Stella and her Uncle Buster help restore a 1950's teen-age hangout to it's original glory despite Flora Reilly's plans to bulldoze it and erect a monument to herself!
A handsome newspaper publisher named Tom Meecham gets on Flora's bad side when he prints an editorial in the local paper criticizing one of her companies. To make matters worse, he invites Flora's enemy, Stella Johnson (as his date) to a lavish dinner party thrown by the grand dame herself, where a political debate ensues.