Big Joe Wheelwright and his three sons, Moose, Small Paul, and Henry, ride into town. Sheriff Mattson has called them in and informs Big Joe that he's found the man he's been looking for. He directs them to the El Dorado Saloon where Bart Maverick is playing poker. The owner, Matthew Braze, jokes with Big Joe, who isn't amused. Big Joe sends Small Paul and Moose off and then has Henry offer to sit in on the poker game. When Bart notes that there's no room, Big Joe snaps his finger and has one of the local players get up to make room for his son.
Henry offers Bart a thousand dollar bill and "accidentally" claims that it's a hundred. When Bart points out his mistake, Big Joe is impressed with his honesty. Small Paul offers Bart a drink but he refuses, saying that he prefers playing sober when he's on the job. As Big Joe applauds Bart's temperance, Moose starts assaulting a bar girl. Bart isn't particularly interested in getting involved until Mattson prods him into action by threatening to shut down the poker game if Bart doesn't help. Bart punches Moose, who barely notices, and then Moose punches him back. Big Joe is impressed when Bart (barely) manages to remain standing.
The Wheelwrights take Bart to his room and Big Joe informs him that he passed their tests and they want to hire him. As he plans to move on, in order to keep up his good luck streak, Bart declines the offer. The Wheelwrights leave, seemingly satisfied. However, when Bart goes to catch the next stage, Mattson arrests him for loitering. When Bart points out that two drunken cowboys are shooting up the town, Mattson explains that the Town Council just passed a new anti-loitering law... and the Wheelwrights and their workers make up the Council. Big Joe is the Justice of the Peace and fines Bart everything he has and sentences him to two years of hard labor... unless he takes the job.
Bart reluctantly agrees and Big Joe explains that he's purchased three wives for his sons from a marriage broker, Harry Whittleseed. Whittleseed is bringing them from San Francisco but the Wheelwrights have to leave town to deal with a crooked foreman at one of their mines. Big Joe wants Bart to chaperon the three "refined" ladies until they return - warning that there are some townspeople that would like to humiliate the Wheelwrights and that Bart must make sure the women are as "refined" as they should be.
Having no choice but to take the job, Bart meets Whittleseed at the stage and welcomes the three wives-to-be: Cissie, Lou Ann, and Emma. After collecting his fee and having Bart sign for the women, Whittleseed holds a whispered conversation with the three of them before leaving. As he goes, Braze watches from the saloon window. Meanwhile, Emma informs Bart that they can't live in a dump and are going back to San Francisco. He insists that it's a peaceful town and then they hear a gunshot. Bart and Mattson go to investigate and find Whittleseed dead and the broker's fee missing.
Bart makes arrangements for the women to stay in town but Emma informs him that they've decided to stay after all. They go to the Wheelwright's spread, the Sub Rosa Ranch. Meanwhile, Braze's man Humbolt reports to his boss and gives him the money. Braze berates him for killing Whittleseed against his orders but Humbolt says he didn't have a choice. He gives Braze a letter that he took from Whittleseed and Braze reads it and says he's going to the Sub Rosa.
At the ranch, Emma tells Bart that they're leaving after all. When he tries to stop them, Lou Ann knocks him out with a wine bottle. He wakes up and discovers that the women are robbing the house. An armed Emma explains that Whittleseed couldn't find enough "refined" ladies so he hired Emma, who is actually a stranded actress and that Cissie and Lou Ann are unemployed bar girls who Emma recruited. The plan was that Whittleseed would collect the broker's fee, the women would find a reason to leave, and they'd all meet and split up the money. However, now that Whittleseed is dead, Emma came up with a new plan and decided to rob the Wheelwrights. Bart warns that Big Joe will do everything he can to have them arrested and suggests that they go with the original plan but split Bart's chaperon payment instead. The women agree but it's clear that Cissie and Lou Ann will need a lot of refinement.
While Bart drills Cissie and Lou Ann in etiquette, Braze slips in and visits Emma. He shows her the letter he took from Whittleseed which describes the entire scheme. Braze offers to help them go through with the marriage. He gets rid of Big Joe, his rival, while the women gain control of the Wheelwright financial empire founded by their grandfather, Four-Square Wheelwright. Emma worries that Bart will blow the deal but Braze figures that once Bart collects his fee, he'll leave the town and be out of their hair. Emma hesitates but then agrees to the deal.
The next morning Bart comes down for breakfast and discovers that Lou Ann and Cissie are now prefect ladies. Emma explains that she had a long talk with them. The Wheelwrights arrive that night and the three sons meet their new wives. Everyone gets along: Henry with Cissie, Small Paul with Lou Ann, and Moose with Emma. Big Joe is satisfied and agrees to double Bart's fee...after the weddings. Bart would rather collect the fee now and suggests to Emma that she find a way to break off the engagements. He figures that Big Joe won't hold it against him if the women break it off. Emma stalls for time and tells Bart they'll do it in the next few days.
After three days, however, the happy couples are still happy. Emma tells Bart that they can't bring themselves to break up with the Wheelwrights because they're so sweet. Bart tries to break up the couples on his own. First he tells the shy Moose that Emma likes a dominating man. Then he spills cream on Lou Ann's dress and tries to blame it on Small Paul. However, the youngest Wheelwright says he'll buy Lou Ann plenty of dresses and goes back to sharing her rock candy. Finally, Bart tells Big Joe that Cissie is a flirt. He tries to prove it by inviting her for a walk but she's too busy admiring Henry's stamp collection. Meanwhile, Moose makes a bold move on Emma, kissing her. He apologizes but she's impressed and does a little aggressive kissing of her own.
Realizing that his plan has failed, Bart goes to see Emma that evening. He informs her that the weddings will be the next day. Emma admits that she's really in love with Moose, and that Cissie and Lou Ann feel the same about Henry and Small Paul. However, when Big Joe gives Emma his dead wife's necklace for the wedding, she confesses everything to Big Joe and Bart. Furious, Big Joe calls off the weddings and kicks the girls out. They have no choice but to go to Braze and ask for money so they can get back to San Francisco. He tells them that they can raise the money by working for him. When word gets around that the Wheelwrights' fiancées are working for him, Big Joe will be humiliated. Out of options, Emma and the others agree.
Mattson tells the Wheelwrights what Braze is up to. Big Joe goes to confront his rival and tells his sons to stay at the ranch. Meanwhile, Mattson and the brothers tell Bart that since he failed, he'll be going to jail for two years. Realizing that he needs to resolve everything and keep Braze from setting up Big Joe, Bart tries to convince the three brothers to stand up to their father for the first time in their lives. Henry and Small Paul refuse but Moose agrees and tells Bart the family secret: Four-Square Wheelwright was actually a swindler who stole all of the land now owned by Big Joe. Big Joe never lets his sons out of his sight for fear they'll reveal the secret...which Moose has just revealed. Moose tells his brothers that he's had enough and that he's going to do what's right and rescue his fiancé. He heads for town and Bart suggests that Small Paul and Henry do the same.
At the El Dorado, the male townspeople are "celebrating" with Emma, Cissie, and Lou Ann. Big Joe and Mattson arrive and Braze makes it look like Big Joe is trying to harass his employees and start a fight. Big Joe loses his temper and Braze accuses him of assault. Every man in the room is in Braze's pay and gets up to take on Big Joe. The Wheelwright patriarch is ready to fight them all but his sons and Bart arrive. Big Joe admits that he's glad to have them there even though they disobeyed his orders. The three brothers take on everyone in the bar with Moose handling a dozen men. Big Joe offers Bart a cigar and advises him to watch the proceedings. However, when Braze tries to shoot Big Joe, Bart tackles him. Braze and Humbolt try to escape and Small Paul goes after them. Humbolt goes for his gun and Bart knocks him out with a well-thrown railing ball.
Once the Wheelwrights win the fight, Emma explains that Braze found the letter describing the scheme and used it to make them work against the Wheelwrights. The brothers don't care and insist on going through with the weddings. Big Joe objects but Bart threatens to reveal Four-Square's secret unless Big Joe backs down. Giving in to the inevitable, Big Joe accepts his three new daughters-in-law.