Trading Places

Brothers Randolph and Mortimer Duke own a successful commodities brokerage in Philadelphia. They witness an encounter between their managing directorâthe well-mannered and educated Louis Winthorpe III, engaged to the Dukes' grand-niece Penelopeâand street hustler Billy Ray Valentine, who Winthorpe has arrested for suspected robbery. Holding opposing views on the issue of nature versus nurture, the Dukes make a wager of the "usual amount" and agree to conduct an experiment switching the lives of Winthorpe and Valentine and observing the results.
Winthorpe is publicly framed as a thief, drug dealer, and adulterer by Clarence Beeks, who works for a security company hired by the Dukes. Winthorpe is fired from Duke &amp; Duke, his bank accounts are frozen, he is denied entry to his Duke-owned home, and is vilified by Penelope and his former friends. He befriends prostitute Ophelia, who agrees to help him in exchange for a financial reward once he is exonerated. Meanwhile, the Dukes bail Valentine out of jail, install him in Winthorpe's former job, and grant him use of Winthorpe's home. Valentine learns the business quickly, using his street smarts to achieve success, and begins to act well-mannered.
During the firm's Christmas party, Winthorpe is caught planting drugs in Valentine's desk in a desperate attempt to get his job back, and he brandishes a gun to escape. The Dukes discuss their experiment in the men's bathroom, and settle their wager of "the usual amount": one dollar. They plot to return Valentine to the streets. Valentine overhears the conversation and seeks out Winthorpe. Winthorpe attempts suicide by overdosing on pills. Valentine, Ophelia and Coleman (Winthorpe's butler) nurse him back to health, and inform him of the Dukes' experiment. On television, they learn that Beeks is transporting a secret USDA report on orange crop forecasts. Winthorpe and Valentine recall large payments made to Beeks by the Dukes, and realize that the Dukes plan to obtain the report to corner the market on frozen orange juice.
On New Year's Eve, the four board Beeks' Philadelphia-bound train, intending to switch his report with a fake. Beeks uncovers their scheme and attempts to kill them, but he is knocked unconscious by a gorilla who is being transported on the train. The four disguise Beeks with a gorilla costume and lock him up with the real gorilla. The fake report, which says the year's orange crop will be low, is delivered to the Dukes. Valentine and Winthorpe travel to New York City with Coleman's and Ophelia's life savings to carry out their part of the plan.
On the commodities trading floor, the Dukes commit all their holdings to buying frozen concentrated orange juice futures contracts; other traders follow their lead, inflating the price. Meanwhile, Valentine and Winthorpe sell futures heavily at the inflated price. Following the broadcast of the actual crop report, showing that the orange crop will be normal, the price of orange juice futures plummets. Valentine and Winthorpe close their futures position by buying futures at the lower price from everyone but the Dukes, turning a large profit. The Dukes fail to meet a margin call, and are left owing $394 million. Valentine and Winthorpe explain to the Dukes that they had made a wager on whether they could simultaneously get rich while making the Dukes poor. Valentine collects $1 from Winthorpe while Randolph collapses holding his chest as Mortimer shouts angrily at his brother about their failed plan.Beeks and the gorilla are loaded onto a ship heading for Africa. The now wealthy Valentine, Winthorpe, Ophelia and Coleman vacation on a tropical beach.

Question: Who is caught planting drugs in Valentine's desk?
Answer: Winthrope