The film is centered on the friendship between three women who work in the business offices of a large corporation known as Consolidated, located in Chicago. Judy Bernly (Jane Fonda) is a na´ve new employee, a recent divorcee whose husband left her for his secretary. On her first day, Judy meets Violet Newstead (Lily Tomlin), the supervisor of her department, and a longtime employee of Consolidated. Violet trains Judy and introduces her to the department executive, Franklin Hart, Jr. (Dabney Coleman), who immediately reveals himself to be arrogant and sexist. Judy soon learns that Violet, an employee for over 10 years, has been passed over consistently by those who could promote her, and in fact she has seniority over Hart.
The third woman in the trio is the buxom Southern belle Doralee Rhodes (Dolly Parton), Hart's personal secretary. Despite the fact that Doralee is happily married to a construction worker and part-time country-western singer, and Hart is also married to a sweet but oblivious woman named Missy, Hart continually makes inappropriate advances toward Doralee, pushing her patience and tolerance to the limit. Hart has also been lying to his colleagues that he's been sleeping with Doralee, causing office gossip to go wild. The women in the office treat her rudely as a result, and initially Judy shuns Doralee's attempts to be friendly.
Some time passes, and Violet is once again passed over for an important promotion, even though her ideas are good enough that Hart passes one off as his own and takes all the praise for it. When Violet protests to Hart that he passed her over for a promtion because she is a woman, Hart bluntly tells her that the company would rather have a man in the position, and Violet becomes enraged, storming off on her own, but not before she reveals to Doralee that her affair with Hart is common knowledge. Doralee, who has been confused and upset about the way she's treated by her coworkers, snaps and also rages at Hart, threatening to use her gun on him the next time he makes an indecent proposal. Judy witnesses a fellow secretary lose her job over a minor infraction and she, too, becomes enraged.
The three women converge at a local bar to drown their sorrows, when Violet discovers a marijuana cigarette that her son left in her purse as a gift. They return to Doralee's house and smoke it together, prompting each of them to have a detailed fantasy about how they would kill Hart if they had the chance. Judy imagines a scenario where she's a great white hunter who hunts down Hart in the office with a shotgun. Doralee's fantasy is of her as a cowgirl who turns the tables on Hart and sexually harasses him before roasting him alive on a spit. Violet envisions a fairy tale where she is a Snow White type character who poisons Hart's coffee and sends him falling to his death outside his office window, which suddenly releases scores of oppressed "prisoners" chained to their desks.
Things take a sudden bizarre turn the next day when each of the women's fantasies comes true in some odd way. Violet accidentally and absent-mindedly puts rat poison in Hart's coffee, mistaking it for an artificial sweetener. Before Hart can drink it, he falls from his unstable desk chair and knocks himself unconscious in his office. Doralee finds him and calls for an ambulance and accompanies him to the local hospital.
At first the women have no clue what happened to Mr. Hart, but then Violet finds the rat poison and realizes what she did, and they all assume the reason Hart blacked out was because he drank the poisoned coffee. They embark on a wild nighttime chase to cover up the crime, starting when Violet steals what she thinks is Mr. Hart's body out of the hospital and puts it in the truck of her car to dispose of it. Only after they get into a minor car accident do they discover that the corpse is not that of Mr. Hart. After shaking off a suspicious policeman, the three women dispose of the body by taking it back to the hosptial and leaving it in a wheelchair in a restroom.
The nexy day, they discover that Hart wasn't harmed at all, but their discussion about the incident is overheard by Hart's nosy personal assistant, Roz Keith (Elizabeth Wilson), and Hart tries to use the information to blackmail Doralee into having an affair with him after all. Doralee loses her temper and ropes Hart with telephone wires, and Judy fires on Hart with Doralee's pistol gun when he escapes his bonds.
With Hart's wife away on a lengthy cruise, the women decide to kidnap Hart and imprison him in his own home until they can somehow get him to cooperate and forget the whole incident. But the cold and impassive Hart refuses to listen to them and vows to kill them. Looking for a way to blackmail Hart to keep quiet, Violet discovers that Hart has been embezzling money from Consolidated by illegally selling inventory from a Consolidated-owned warehouse and keeping the profits for himself. The girls plan on using the information to blackmail Hart to keep quiet from calling the police.
After purchasing a series of items, including a skydiving harness, chains, dog collars, and a remote-controled hook and wire to keep Hart confided in his own house, the ladies return to work after the weekend as usual while Violet sends for an order of the warehouse inventories as proof of Hart's embezzlement scheme, but she soon learns from the head office in New York that, because of a computer system change, the office will not send them the invoices for between four to six weeks.
From this point on, a race is on to see if Hart can escape or if Violet's documented proof of the scam will arrive in time. The three women work together to make Hart's absence in the office as inconspicuous as possible, and they send Roz to Europe on a ruse to learn a foreign language to keep her away from the office. During the weeks of Hart's confinment, the three ladies take a number of liberties in improving the workplace in ways that they see fit.
One night, Hart almost escapes when he finds a nail file in the bathroom the ladies overlooked and tries cutting his restraints. Judy, who is staying nights in Hart's house, is surprised when her ex-husband shows up at the house after following her there after work and he asks to reconcile with her. But when Hart makes a noise, Judy is forced to restrain him and her ex-husband, seeing the captive Hart tied up, mistakenly assumes that Judy is having an affair of her own with her boss and leaves, claiming that they are now over and will never get back together.
Later, Hart is accidentally freed when Missy returns early from her cruise, and for three days, he quietly buys back all the items he sold and puts them back in the Consolidated warehouse. Doralee only learns about Hart's wife's return when Mrs. Hart calls her at her house to thank for her sending her flowers in Hart's name which is why Hart's wife, Missy, returned from her vacation earlier since Hart treats her badly. Doralee runs over to the house to find the freed Hart now holding Judy captive.
After taking them to the office to meet with Violet, Hart plays his final card boasting that women never can defeat him. Just when it appears as if he is going to send the girls to jail, a sudden visit from the reclusive and ruthless Chairman of the Board, Russell Tinsworthy (Sterling Hayden), interrupts him. To the cold and unfeeling Hart's chargrin, he finally sees that Violet, Judy, and Doralee have made some radical changes in the office while keeping him imprisoned, and it seems as if the sudden surge in productivity has caught the attention of Tinsworthy.
Since the women did all of it under the false approval of Hart, they can take no credit for it, but fate seems to be on their side: Tinsworthy "rewards" Hart for his good work by immediately removing him from his position and sending him to work on a special project in Brazil, much to the amusement and delight of Violet, Doralee, and Judy as now they are free from Hart who will never try to destroy them without destroying his own career.
In a postscript at the end, it is revealed that Violet took Hart's place as vice president of Consolidated, Judy married the Xerox repairman and quit the company, Doralee also quit the company and moved back to her Tennessee hometown where she became a country music singer (just like the actress that played her), and Hart was kidnapped by natives during a trip in the Amazon and was never seen or heard from again.