While multimillionaire airline owner Tom Mullen (Mel Gibson) attends a science fair in Central Park that his wife Kate (Rene Russo) is judging, their son Sean (Brawley Nolte) is kidnapped. Sean is taken to an apartment by Maris Conner (Lili Taylor), who previously worked for Mullen as a caterer at a party, along with small-time criminal Cubby Barnes (Donnie Wahlberg), Cubby's older brother Clark (Liev Schreiber) and high-tech criminal Miles Roberts (Evan Handler). Tom and Kate receive an untraceable email from the kidnappers, demanding $2 million as ransom. Tom calls the FBI, who set up a base of operations in his apartment.

Detective Jimmy Shaker (Gary Sinise) of the NYPD is arresting a perpetrator in a convenience store when Cubby comes in and nervously buys some FrankenBerry cereal. Shaker follows Cubby into the building where the kidnappers are residing; Shaker is the mastermind behind the kidnapping and is romantically involved with Maris. He chides Cubby for buying a box of kids' cereal in front of cops during a kidnapping investigation. The group argues over the plan to kill Sean once the ransom has been delivered. Cubby tells Clark that he plans to release Sean despite the risk of identification.

Tom agrees to the FBI instructions for delivering the ransom. Receiving an untraceable phone call from Shaker (electronically disguising his voice), Tom follows his instructions. Tom meets Cubby in a New Jersey quarry. Shaker indicates that Cubby is supposed to give Tom an address where Sean can be picked up in exchange for the money, but when Cubby appears ignorant of these instructions and simply demands the cash, Tom refuses to hand it over. The FBI sends a helicopter to follow Cubby, and Cubby opens fire. FBI marksmen shoot Cubby; he dies before he can reveal Sean's location to Tom.

Shaker calls again, setting up another ransom drop. Angered that the FBI followed him instead of the money as they had promised and killed his only lead, Tom insists on taking the money without being tracked. En route to the location, he realizes the first drop was a setup, and there is no guarantee that Sean will come back alive. Tom drives to a local TV station, going on the news and explaining that he refuses to pay the kidnappers, instead offering the $2 million ransom as a bounty on their heads. The only way for them to save themselves is to return his son, in which case he will withdraw the bounty and drop all charges.

Shaker sends an anonymous message to Kate, luring her to a meeting in a church where he attacks her from behind, and tells her to pay the ransom or Sean will die. Tom sticks to his plan, sure that it is the best chance of having Sean returned, despite the pleadings of Kate and FBI Special Agent Hawkins (Delroy Lindo). He responds by upping the bounty to $4 million. Shaker calls Tom and demands to be paid, or else Sean will die. Tom replies that Sean must be returned or else the kidnappers will be hunted down. Tom hears Sean's voice screaming for his father. Shaker fires a shot that is heard over the phone before the call cuts off, leaving Tom and Kate to believe their son is dead.

Shaker forms a new plan—he will kill Clark and Miles, pretend to rescue Sean, and claim the $4 million bounty for himself and Maris. He calls in an armed robbery to the NYPD, requesting backup. Clark and Miles realize he has betrayed them and try to drive away, but Shaker manages to move to the driver's side and shoot Clark, stopping the van. He then shoots and kills Miles, and makes it look as though Miles shot at him. He is then shot by Maris, wounding him in the shoulder. (Maris had been trying to back out of the plan.) As she raises her gun a second time, Shaker kills her and calls for backup, announcing he's rescued Sean. The SWAT team storms the apartment where Sean was held, finding a wounded Shaker sitting next to Sean. (He is careful that Sean never hears his voice, while he is sure that Sean, who was always blindfolded, won't recognize his face. But Shaker talked in front of the boy when the cops came to get him out.)

Tom and Kate are grieving for their son when Hawkins approaches and takes them to the scene of Sean's "rescue". Tom thanks Shaker, who is being taken to the hospital. Hawkins takes Tom to Maris's body, where it is revealed that Tom knew her through the airline business. He knew her because she worked in his apartment several times when they had catered parties. Shaker is questioned by Hawkins about the shooting of the kidnappers. He claims Miles shot at him and Clark tried to run him over. When questioned about Maris he says a bullet hit him and spun him around, and he did not realize who he was shooting at.

A few days later, after placing a backup revolver around his ankle, Shaker unexpectedly appears at the Mullens' apartment to receive the reward, claiming he wants to avoid the press. As Tom writes a check for him, Sean recognizes Shaker's voice. Seeing his son's reaction and hearing Shaker recite the phrase "Shouldn't be a problem" exactly like the kidnapper did, Tom and Sean realize that Shaker is the kidnapper. Tom gives Shaker the check with a false signature, but Shaker realizes that Tom is on to him. Shaker decides to kill everyone in the house, but Tom convinces him to take him as a hostage and go to the bank so Tom can wire the money to Shaker's account. En route, Shaker orders Tom to get his private jet ready. Tom fakes a call to his pilot, actually calling Hawkins, whom Tom manages to tell in code that the kidnapper is with him.

Cops converge on Tom and Shaker outside the bank. Shaker panics and opens fire, killing several cops. Tom throws himself at Shaker and Shaker loses his gun to Tom. Tom throws Shaker through a store window and when they emerge they are surrounded by armed policemen. Shaker draws his back-up revolver from an ankle holster. Tom and Hawkins fire first, killing Shaker. The film closes as Hawkins stops the police from arresting Tom.