In New Orleans, Louisiana, Celeste Wood's life is changed in a blinding flash when a failed day trader at her husband's stock brokerage firm shows up at his former workplace with a semiautomatic handgun and opens fire on his former colleagues, including Celeste's husband. Two years later, and armed with pro bono attorney Wendell Rohr (Dustin Hoffman), Celeste decides to take the weapon's manufacturer to court, on the grounds that the company's gross negligence led to her husband's death.
As the trial date draws near, jury consultant Rankin Fitch (Gene Hackman) arrives in town. Early in the movie, Fitch proves his incredible talent for reading people when he correctly guesses that his cabbie's mother is ill and in the hospital. Fitch arrives at his destination: the back room of a closed costume shop. In this room are about a dozen people on Fitch's payroll, armed with personal computers and backgrounds on each of the jurors in the jury pool. Also in this room are viewing and listening devices, intended to allow Fitch and his staff to communicate with lead attorney Durwood Cable (Bruce Davison) in the courtroom through electronic surveillance (a highly illegal practice) when they view the jurors and hear the answers to the questions put forth to them.
In the jury pool is Nicholas Easter (John Cusack), a happy-go-lucky video game store clerk who tries to get himself excused from jury duty, even going as far as asking the judge to excuse him so he can compete in a video game challenge with a nominal cash prize. The judge refuses, and Fitch, despite doubts about allowing Easter on the jury, is out of challenges and has no choice but to allow Easter into the jury.
Easter's congenial manner wins him acceptance from his fellow jurors, except Frank Hererra, a hardened former Marine of Cuban descent, who knows that there is a great deal of money at stake. Hererra takes an instant disliking to Easter, which is not alleviated when Easter proposes Herman Grimes - a blind man who displayed the most knowledge of law out of all of them when being selected - as jury foreman instead of Hererra.
However, there is something to Hererra's suspicion that Easter has a hidden agenda. It is soon clear that Easter does have an ulterior motive, which somehow involves his girlfriend Marlee (Rachel Weisz). The two seem to be grifters and try to offer Fitch the verdict he wants - for a steep price. Fitch, clearly not amused, asks for proof that they can do what they say they can do. This they try to give him in a number of different ways; for example, Marlee asks Fitch "feeling patriotic?" and the next day, as an indirect result of a suggestion of Easter's, the jury stands up and leads the entire courtroom in the Pledge of Allegiance.
Angered that an "amateur" may be even better at manipulating the jury than he is, Fitch orders Easter's apartment raided. Marlee counteracts by getting one of Fitch's jurors bounced. The cat and mouse game continues when a hit man tries to kill Marlee in her apartment. She manages to injure the intruder and escapes. She raises her price from $10 to $15 million.
Meanwhile, Marlee is also working on Rohr, also promising to deliver him the same verdict for the same price. Though Rohr knows his case stands little chance against the well-funded defense- indeed, he goes so far as to actually get the money out-, he refuses to pay, going with his conscience.
Fitch finally agrees to pay Marlee the ransom as one of his witnesses blows up on the stand, crippling, but not entirely losing the case. After Easter receives confirmation that Fitch has wired the money to a Cayman Islands bank, he asks jurors to review the facts of the case (trying to deliver a conviction for Celeste), much to the displeasure of his fellow juror Frank. In the meantime, Fitch's henchman, tracking Easter's path to Indiana, calls him frantically, telling him to not wire Easter the money, but it is too late. The henchman also learns that Easter's real name is Jeffrey Kerr, and that he has been tailing gun cases for some time. We also learn that Marlee's real name is Gabrielle Brant.
Obviously Marlee and her sister had been Easter's friends since high school in the fictional rural town of Gardner, Indiana. Marlee's sister died in a school shooting when Easter was unable to protect her, and the town took the gun manufacturer to court in a lawsuit that Fitch himself argued. The town bankrupted its treasury after losing the case to Fitch.
Back in the jury room, Frank calls the lawsuit frivolous, stating that despite the hardship in his own life, he has never asked anyone for a handout. Frank also reveals in a rant that regardless of the case facts, he does not want to deliver a verdict that will make a white upper-middle class woman even richer.
Shocked at Frank's outburst, the jurors agree to review testimony once more. The gun manufacturer is found liable, with a large jury award coming for Celeste Wood. Fitch, defeated, leaves the courthouse and into an area bar. There, he is confronted by Easter and Marlee, who show him a copy of the wire transfer of $15 million. They tell him that he is to retire immediately... or they will fax the transfer document to the IRS, who will be likely concerned over such a large amount of money. Fitch asks what they intend to do with the money, and gets the answer that the $15 million will be given to the town of Gardner, Indiana since they went bankrupt after losing their case.
Outside the bar, they see Wendell Rohr. Rohr recognizes Marlee and knows it's Nick with her. They smile at one another without saying a word. The movie ends with Marlee telling Nick she wants to go home. Nick agrees, knowing their job is done.