Louis Winthorpe III, a young stockbroker, is awakened to breakfast in bed by his butler, Coleman, in his opulent Philadelphia, Pennsylvania townhouse. As Coleman shaves his face, Winthorpe predicts that pork bellies will have an exciting morning in the market. Meanwhile, brothers Randolph and Mortimer Duke are greeted by servants and leave their estate in a chauffeured Rolls Royce. Reading Science Journal , Randolph complains about the debate pitting heredity vs. environment in the study of human behavior, but Mortimer tells his older brother that he is tired of his theories. Uncertain about Winthorpe’s pork belly estimates, Mortimer decides to sell their shares early, but Randolph tells him to wait. They watch the numbers rise on the limousine’s television monitors, and their company, Duke & Duke, profits $347,000. When the Duke brothers arrive at the Heritage Club, they are approached by Billy Ray Valentine, a blind, Vietnam veteran amputee, who wheels himself towards them on a board. Begging for change, Mortimer rejects Valentine’s pleas and hits him with his Wall Street Journal . Winthorpe meets Randolph and Mortimer at the club with the Duke & Duke payroll and Mortimer complains about the amounts, but Winthorpe reminds him that they cannot get around minimum wage. Winthorpe inquires about a $50,000 check for Clarence Beeks, a man who is not employed at the firm, but the brothers reticently inform Winthorpe that Beeks is conducting top-secret research. Changing the subject, Mortimer asks about Winthorpe's fiancée, Penelope, who is the Duke brothers' grandniece. When Winthorpe leaves, Mortimer comments that he is a good man, but Randolph argues that Winthorpe is merely a product of his privileged upbringing. Outside, Valentine is approached by two police officers that lift him from the board and expose his legs. Valentine thanks them, and Jesus, for the miracle and walks away, but crosses paths with Winthorpe in front of the club and knocks him over. Picking up Winthorpe’s briefcase in the attempt to assist him, Valentine is accused of being a thief and runs into the club to escape the police. After Valentine is handcuffed, Randolph asks him about his background, and as he is led away, Randolph concludes that Valentine is not a bad man but the victim of a poor environment. Eager to prove his theory, Randolph bets Mortimer that Valentine would be as successful as Winthorpe if they traded places in society, and that Winthorpe would resort to a life of crime if put in Valentine’s position. Claiming that the experiment is a good cause, the brothers agree to manipulate the lives of Valentine and Winthorpe and reverse their roles, wagering “the usual amount”: one dollar. Later, at dinner with Penelope, Winthorpe casts himself a hero as he recounts the encounter with Valentine at the club, and she propositions him. Coleman receives a call from the Duke brothers, informing him of their “scientific experiment” and he agrees to follow orders because they are the owners of the house and he works for them. As Winthorpe and Penelope undress, Penelope inquires about the date of their engagement party, on January 2, but Winthorpe tells her it’s the busiest day of the year for commodity trading because the crop reports are released. The next day, Valentine narrowly escapes a fight in his prison cell when the Duke brothers bail him out. Outside, Randolph and Mortimer lure Valentine into their limousine by telling him they posted his bail. Claiming to belong to a charity organization, the Duke brothers offer Valentine a house, a bank account and a job with an $80,000 salary. After receiving confirmation from the chauffeur that the brothers are not homosexuals, Valentine agrees and the Duke brothers take him to Winthorpe’s home, introduce him to Coleman and explain that everything he sees belongs to him. Despite his discomfort in the new role, Valentine accepts a bath and dresses in Winthorpe’s suit. Later, at the instruction of the Duke brothers, Beeks plants marked $50 bills in Winthorpe’s coat pocket and exposes him as a thief at a Heritage Club meeting. Despite his protests, Winthorpe is arrested, and after Beeks talks to an officer, the police find PCP in his jacket. Meanwhile, Valentine goes to a bar to settle his debts, buys champagne and invites everyone back to the townhouse. Disturbed by his guests’ lack of respect, Valentine kicks them out and tells Coleman that they were freeloaders. The next day, Winthorpe is bailed out of jail by Penelope, who is mortified by his appearance. On their way out of the police station, Penelope tells Winthorpe that he has been fired from Duke & Duke and that they are pressing charges of embezzlement when Ophelia, a prostitute who has been paid off by Beeks, kisses Winthorpe and begs him for drugs. When Penelope deserts him in anger, Ophelia tells Winthorpe that she was paid $100 for the joke and they take a cab to his house, where he promises to give her $50 in exchange for the fare. Upon arriving, however, Winthorpe’s key does not fit the lock and Coleman feigns ignorance of his identity. At the bank, Winthrope discovers that his accounts were frozen by the IRS and his credit cards are repossessed. Desperate, Winthorpe begs Ophelia to help him, and after examining his unworn, manicured hands, she decides to trust his story. In the taxi, Winthorpe and Ophelia cross paths with Valentine, who is in Winthorpe’s limousine on his way to work. The two men recognize each other and Valentine becomes increasingly suspicious about his new circumstances. At Duke & Duke, Rudolph and Mortimer explain the commodities business to Valentine, and Valentine likens them to bookies. As Ophelia and Winthorpe return to her apartment, Winthorpe accuses Valentine of masterminding his downfall, but Ophelia cuts him off and says she expects financial reciprocation for her assistance. He is shocked to learn that she is a prostitute and that she has saved $42,000 for an early retirement. Meanwhile, Valentine surprises the Duke brothers with his accurate intuition that pork belly prices will decrease. As they leave the office, Mortimer tests Valentine by dropping his money clip, but Valentine quickly returns it. Dressed in mismatched clothes borrowed from Ophelia, Winthorpe goes to the club and asks his friends to testify on his behalf and to loan him money, but they refuse and Penelope asks him to leave. At a pawnshop, Winthorpe gets $50 for his expensive watch and buys a gun. Later, in a rainstorm, Winthorpe gets a fever after spotting Valentine at a fancy restaurant with the Duke brothers, and Ophelia cancels her work to care for her “investment.” After seeing Valentine’s new appointment announced in The Financial Journal , Winthorpe disguises himself as Santa Claus and infiltrates the Duke & Duke Christmas party. Meanwhile, Valentine notices a $10,000 payroll check for Beeks. When he confronts the Duke brothers, Randolph remarks to Mortimer that Valentine is working late on Christmas Eve and expects to win the Nobel Prize for his success in the wager, but Mortimer reminds Randolph that they have not seen evidence that the “second party” has turned to crime. Returning to his office, Valentine catches Winthorpe planting drugs in his desk drawer. Winthorpe attempts to convince the Duke brothers that Valentine is a drug dealer and has stolen his livelihood, but when Valentine calls security, Winthorpe threatens him with his handgun and runs from the party, terrifying the guests in the process. Valentine expresses no empathy for Winthorpe’s predicament, then lights one of Winthorpe’s joints in the bathroom. Concealed in a stall, Valentine overhears the Dukes settle their wager and discuss how to return him to the ghetto. They decide to wait until after they receive the crop report on New Year’s Eve, and mention that Beeks’s clandestine services will bring them great success. Valentine follows Winthorpe as he drunkenly stumbles through traffic. After a dog urinates on his shoe and it starts to rain, Winthorpe attempts suicide, but his gun does not fire until he casts it aside. Back at Ophelia’s apartment, Valentine and Ophelia find Winthorpe in the bathtub, overdosed on pills, and Valentine brings him back to the townhouse for medical assistance. When Winthorpe wakes up in his old bed with Coleman at his side, he assumes the experience was a nightmare, but when he sees Valentine, he attempts to strangle him. Valentine explains that the Dukes used them as guinea pigs in their experiment and Coleman concurs. Learning that his life was ruined for a $1 bet, Winthorpe loads rifles in preparation for a violent revenge, but Valentine suggests that they retaliate against the Dukes by usurping their fortunes. On a television news report, they see Beeks delivering the orange yield estimates for the annual crop report and Ophelia identifies him as the man who paid her off to seduce Winthorpe. Realizing that the Dukes bribed Beeks to leak the report, Valentine, Winthorpe, Ophelia, and Coleman conspire to upset their plan. From his office, Valentine eavesdrops on a phone call between the Dukes and Beeks and learns that Beeks will be traveling from Washington, D.C. to New York by train the following day and meeting the brothers in the orange section of the Hilton Hotel’s parking structure. On Beek’s train, passengers are dressed in costume for a New Year’s Eve party, and he watches as baggage handlers bring a caged gorilla onboard. Valentine, Ophelia and Coleman enter Beeks’ cabin in disguise and swap his briefcase for a decoy. After Valentine delivers the case to Winthorpe in the men’s room, Winthorpe enters the cabin in blackface, dressed as a Rastafarian, but Beeks observes him replace the briefcase and takes Ophelia hostage. As Beeks directs the group through the costume party, a man in a King Kong costume flirts with Ophelia and follows them into the baggage car. Standing in front of the gorilla cage, Beeks threatens the group, but when he hits the man dressed as King Kong, the animal defends his fellow gorilla and knocks Beeks unconscious. Coleman holds Beeks at gunpoint while Ophelia, Valentine and Winthorpe bind and gag him. They leave Beeks in the gorilla’s cage, dressed as King Kong, for the gorilla’s pleasure. At the Hilton parking garage, Valentine impersonates Beeks and exchanges a falsified report for a briefcase filled with cash. Seeing Winthorpe and Valentine off at the train station on their way to the New York Stock Exchange, Coleman and Ophelia give them their life savings and Ophelia and Winthorpe kiss good-bye. Arriving at the World Trade Center, Winthorpe briefs Valentine on trading techniques as they resolutely hit the floor while the Dukes act on inaccurate data from the report and instruct their broker to aggressively purchase orange juice stock even as the price increases, despite his warning that the crop reports will not be broadcast for another hour. As trading begins, investors assume the Dukes are attempting to corner the market, and buy frantically. When the price hits $142 a share, Winthorpe and Valentine sell and the crowd bombards them. Watching the prices drop, the Dukes realize Winthorpe and Valentine have outwitted them. As Randolph and Mortimer desperately cross the floor to reverse their orders, the trading frenzy subsides for a televised presentation of the Department of Agriculture’s estimates of the coming year’s orange crop yield. Learning that the winter has not effected the harvest and crops are plentiful, the brokers clamor to sell. The price of shares hits rock bottom and Winthorpe and Valentine buy at a huge profit. When the market closes, Valentine explains to Randolph and Mortimer that he bet Winthrope $1 that they could get rich while financially ruining the Dukes, and Winthorpe forfeits his loss. As Randolph and Mortimer are unable to pay the $394 million from the day’s trading, their seats in the market are put up for sale and their assets are seized. Realizing they have lost everything, Mortimer belligerently protests while Randolph has a heart attack and collapses. Meanwhile, Beeks is shipped to Africa with his gorilla mate for a science experiment. Valentine, Winthorpe, Ophelia, and Coleman retire with their fortunes to a tropical island.