The original idea for the story was from an episode of "The United States Steel Hour" named "Fearful Decision" that aired in 1954. It was then a remade of the feature length film of the same name (1956) written by Richard Maibaum and Cyril Hume starring Glenn Ford, Donna Reed and Leslie Nielsen. The film also was influenced by King's Ransom, a police procedural novel by Ed McBain which was, in turn, the basis for Akira Kurosawa's 1963 film High and Low.
Tom Mullen (Mel Gibson) is the self-made, wealthy head of a large airline, Endeavor. In events that are not depicted in the film but that become important to the storyline, Mullen acts to head off a labor strike by bribing a union head named Jackie Brown (Dan Hedaya). After the FBI begins investigating, Mullen falsely blames Brown for having initiated the bribe. Tom's lie lands Brown in prison but leads to Mullen and his airline being subject to FBI scrutiny for months. The movie begins as Mullen and his wife, Kate, host a party to celebrate the release of a new Endeavor Airlines commercial for television that features Tom prominently. Shortly thereafter, Mullen's son, Sean, is kidnapped while the family attends an outdoor science fair in Central Park. The kidnappers initially contact Tom and Kate by e-mail, with a video attachment showing Sean tied to a bed and blindfolded. The ransom for Sean's safe return, they are told, is $2 million. At first, the Mullens believe Jackie Brown is behind the kidnapping, but he angrily denies any knowledge when Tom visits him in prison.
A later scene (with a plot twist) reveals that the kidnappers' leader is actually Detective James Shaker (Gary Sinise). Among the kidnappers are siblings Clark and Cubby Barnes (Liev Schreiber and Donnie Wahlberg), two small-time thugs; Maris Connor (Lili Taylor), who is actually the Mullens' caterer and Shaker's girlfriend; and alcoholic computer genius Miles Roberts (Evan Handler), who scrambles the phone lines to stop them from being traced and disguising Shaker's voice through communicating with the Mullens. While the others are either indifferent or hostile to Sean, Cubby talks to Sean and promises him that he will be returned to his parents alive.
The Mullens contact the FBI, led by Lonnie Hawkins (Delroy Lindo). Soon enough, Shaker contacts Mullen and gives him a series of instructions to bring the money to a drop-off point, also promising to give him an address in return. However, at the drop-off, Cubby, who was chosen by Shaker to pick the money up, has no clue of any address, and in the ensuing fight, Cubby is shot and killed by the FBI. At this point, it becomes painfully obvious to Tom that Shaker has no intention of returning Sean even if he receives the money. The kidnappers take Sean to a secluded part of the woods to discuss what they are going to do. His hands are tied behind his back with rope; he is cleave gagged with a piece of white cloth that has duct tape placed over that; and is blindfolded with more strips of duct tape.
Although Clark almost kills Sean in anger (to get revenge on Shaker by ruining his plans), Shaker stops him, and later berates Tom on the phone for breaking the deal. Shaker then gives Tom another set of instructions to follow and drop the money off at a certain point where Clark will be waiting. But on the way, Tom sees his son's face on a television, and makes a change of plan. He appears on television with a message for Shaker: he no longer intends to pay him the $2 million. Instead, he will offer the money as a reward for anyone who finds the man responsible for his son's abduction, and will only withdraw the bounty and drop all charges if his son is returned alive and unharmed, therefore turning the tables on Sean's captors.
After a series of attempts to get Tom to change his mind, Kate is contacted by Shaker via a letter and meets the disguised kidnapper in an old church, where he violently beats her and tells her that if Tom doesn't withdraw the bounty, he will kill Sean. This enrages Tom even further, and he raises the reward to $4 million. Finally fed up, Shaker contacts Tom one last time and tells him to decide whether or not he is going to pay. Tom refuses, and in the ensuing argument over the phone, Shaker fires his gun and hangs up. Tom and Kate immediately assume Sean has been killed as promised, and mourn their son.
Shaker, it turns out, didn't shoot Sean, instead firing at the wall to scare Tom and Kate. Angrily storming out, Shaker goes to a laundrette and betrays his comrades by calling the police about a "possible kidnap situation". Shaker holds his badge in the air, identifies himself as the police and pretends to be attempting to stop Clark and Miles from leaving the scene in their van, but stages a shootout and kills them. Shaker fires several shots from a second gun he was carrying into a nearby wall from Miles's trajectory, then plants the gun in Miles's hand. Just then, Shaker is shot from behind in the shoulder by Maris, angry at what Shaker is doing, and he spins around and makes eye contact with her. Shaker then kills Maris before she can shoot him again. Shaker, hearing the sirens approach, rushes in to the house and falls by the bed where Sean is chained up. Shaker shouts to arriving police ESU units "I'm a cop" and shows his detective's badge. Back at the Mullen's house, Lonnie Hawkins walks out to the balcony to alert the still sobbing couple, who are rushed to the kidnappers' house and are finally reunited with their son. Shaker, who is being taken to hospital, is hailed a hero, and thanked by Mullen.
A few days later, Shaker, knowing it is only a matter of time before he is connected to the kidnapping, goes to Tom's apartment for the $4 million for "finding and rescuing" Sean. Tom, initially surprised Shaker is up and about so soon after being shot, obliges and goes to make out a $4 million bank check. Sean and Kate, who were out in the park, arrive and from another room, Shaker's voice is recognized by Sean. From Tom's vantage point he can see Sean is afraid, giving Tom the message that Shaker was the kidnapper all along. Shaker realizes this as well, but before he leaves with $4 million check Tom quickly gives him, he puts a gun to Tom's head. Shaker wants Tom to wire the money over the phone, but Tom knows Shaker will probably kill him and his family. Tom, with Shaker's gun to the back of his head, vows he will only go with Shaker to the bank and wire it from there. Tom persuades him to spare them and take the $4 million while he still can. Shaker agrees, but on the way to the bank, Tom secretly informs Hawkins that Shaker is the kidnapper, and the police arrive at the bank to arrest Shaker, who starts a gunfight and is chased by Tom and the police through the streets, eventually ending with both Tom and Shaker falling through a glass window. Shaker, now bleeding to death from a neck wound, attempts reach for a gun on his ankle to shoot Tom, but he himself is killed by Tom (who had grabbed Shaker's first gun during the fight) and Hawkins.
The police move in to arrest Tom, but Hawkins stops them.