Jed Clampett, a hillbilly of humble station from Arkansas, accidentally discovers oil on his land while shooting at a jackrabbit. Ozark Mountain Oil, interested in purchasing his land, offers him $1 billion for the property. Unsure of what to do, Jed consults his sister, Pearl Bodine, during a family dinner. Pearl suggests that a change of scenery for Jed's daughter, Elly May, would be a good thing. Pearl and Jethro convince them to move to Beverly Hills California. Ozark Mountain Oil come by Jed's place to check to see if he has signed the contract. Having made up his mind and signed the contract, Jed and his daughter Elly, his mother-in-law, Daisy Moses (aka "Granny"), and his nephew, Jethro, Pearl's son, load up Jethro's old, dilapidated truck with their possessions and move to Beverly Hills, California, even though Granny is reluctant to come.
Milburn Drysdale, the CEO of the Commerce Bank of Beverly Hills (where Jed's money is stored), sends out his secretary/assistant, Jane Hathaway to meet the Clampetts at their new estate that is next door to his. Jane calls the Beverly Hills Police after the Clampetts arrive, mistaking them for burglars. Upon learning of Jane's mistake at the police station, Drysdale briefly fires her. But seeing that Jed insists that he still wants her to watch over his affairs, Drysdale rehires her.
The Clampetts settle into their new surroundings. Drysdale and his wife, Margaret, push their reluctant son, Morgan Drysdale, into befriending Elly May, to whom he eventually develops an attraction. Jane is also smitten by Jethro, who seems ignorant of her affections.
Jed requests Jane's assistance in helping him search for someone who will help turn Elly May into a lady and also wants to get married, so Miss Hathaway has to play matchmaker. Woodrow Tyler, a banker at Drysdale's bank, catches wind of this and contrives a scheme with his con artist girlfriend, Laura Jackson, to steal Jed's money by having her marry Jed. She poses as a French etiquette teacher, Laurette Voleur, and asks for work. 'Laurette' feigns romantic interest in Jed, which eventually leads to him proposing marriage to her.
Shortly before the wedding, Granny hears Laura and Woodrow talking about the scam. Granny reveals herself to the pair and threatens to expose their scam to Jed, and thus the impending wedding will be off. But before she can do so, they capture her, restrain her, and have her institutionalized at the Los Viejos Nursing Home, so that she cannot contact Jed.
At the wedding, Woodrow prepares to transfer all of Clampett's money in Drysdale's bank to a Swiss account, on his laptop computer, when the couple says 'I do'. Realizing that Granny is missing, Jane goes to the office of Barnaby Jones and after learning where Granny is and who Laura is, poses as a nurse and breaks her out. Granny and Jane arrive at the wedding and foil Laura and Tyler's plan when Jane grabs a shotgun and blows the laptop to bits, before they can steal Jed's money. The police arrest Laura and Woodrow. Jed decides that, since the wedding was off, they should have 'one hellacious shindig'.
