In 1999, Seth Davis (Giovanni Ribisi), a 19-year-old who has dropped out of college, operates an illegal yet prospering underground casino from his apartment in Queens. His father, Marty (Rifkin), a federal judge in New York City, is deeply disapproving of Seth's lifestyle, concerned that his son's illicit activities might jeopardize his prestigious position. Striving to earn his father's approval, Seth accepts a job offer from J.T. Marlin, a brokerage firm located in a regular office building near Commack, NY, after Greg Weinstein (Katt) visits him to scout his operation. Seth eagerly becomes a trainee under Greg's guidance.
At first, everything seems to be falling into place for Seth at J.T. Marlin. He is introduced to Jim Young (Ben Affleck), one of the firm's executives, who reveals the secret to accumulating wealth quickly in the brokerage world. Thriving in this new environment, Seth adapts to the company's ways and finds success. In addition to his professional progress, he begins a romantic relationship with Abbie Halpert (Long), Greg's ex-girlfriend, which raises Greg's worries about her influence over their circle of friends. Seth finds himself surrounded by an exuberant lifestyle alongside various affluent stockbrokers like Chris Varick (Vin Diesel) and Richie O'Flaherty (Caan), frequently dining out and engaging in their wild escapades. However, beneath the surface of this glamorous life, Seth grapples with obstacles, including increasingly contentious exchanges with Greg who is concerned about the potential consequences of Seth's rapid success, as well as shutting down the casino due to employee dissatisfaction with their inflated salaries.
Unbeknownst to Seth, the FBI has been keeping a close watch on J.T. Marlin. The brokerage operates as a "chop shop," engaging in unethical "pump and dump" schemes, where brokers produce artificial market demand for defunct or fictitious companies by soliciting investors through deceptive cold calls. After manipulating the stock's price, investors are left without a way to sell their shares, and inevitably, prices collapse. This fraud hits home for one of Seth's clients, Harry Reynard, a family man and purchasing manager at a gourmet food company, who finds himself precariously positioned when Seth sells him shares that quickly lose value.
When Harry reaches out to Seth for an explanation after the market crash, Seth, under pressure from Greg, makes the ill-fated decision to sell him more worthless shares, urging him to invest his entire $50,000 down payment for a new home. Seth's assurances lead Harry into a dire financial fallout that strains his family ties. As the truth about the firm's immoral practices sinks in, Seth becomes increasingly troubled by the deceit he has perpetuated against Harry.
Eventually, Seth's world crumbles when Abbie, in collaboration with law enforcement, betrays him, leading to his arrest by the FBI for violating SEC regulations. In a stunning twist, his father is also implicated for trying to shield Seth during recorded phone conversations. With a deal in place to provide testimony against J.T. Marlin in exchange for federal immunity, Seth finds himself caught in a web of deceit and betrayal. He negotiates the condition that his father stays uninvolved in the case, in return for revealing the firm's dubious tactics.
Seth is released but must return to work the very next day to gather incriminating evidence before the FBI launches a raid. He cunningly saves critical investment files onto a floppy disk before executing a plan to return Harry's money by manipulating the very methodologies he was trained to exploit. In a pivotal moment, he manages to convince Michael Brantley (Scott), one of the heads of the company, to assist him in finalizing a sale ticket that he needs, despite Greg's explicit refusal to help him. As Seth makes his exit, he leaves a note for Chris, warning him of the impending raid. Their exchange signifies a reluctant camaraderie formed in the wake of chaos.
As Seth walks past Abbie in the lobby, he chooses to disregard her, reflecting on his chaotic journey and contemplating his future after severing ties with J.T. Marlin. Outside, the scene escalates as prison buses and FBI agents flood into the parking lot, ready to take action against the firm that once promised him everything.
