Seattle PD Detective Quentin Conners and his partner Jason York are implicated in the death of a hostage taken by a carjacker named John Curtis. After a fellow police officer, Callo, testifies against them, Conners is suspended, and York is fired. In reality, York tried to shoot John, but accidentally killed the hostage. John in turn fired back, but Conners killed John in self-defense.
Some time later, Lorenz and four other criminals take hostages in a bank. Lorenz has only one demand, to negotiate with Conners. Conners is reinstated but put under the surveillance of a new partner, the recently-graduated Shane Dekker. Conners is given control of the negotiations, and after a bank teller is shot, he orders a SWAT unit to cut the building's power and go in. During an explosion, the criminals flee during the ensuing panic and chaos.
Dekker and Conners learn more about each other at a local diner, slowly building a friendship, but Dekker disapproves of Conners' "cowboy cop" methods. Dekker explains that during negotiations, Lorenz was making many cryptic references to chaos theory. As they leave to examine new evidence, Conners puts a ten dollar bill on the table for his share of the bill. Dekker swaps the ten for a twenty of his own. A TV camera caught a shot of one of the criminals, who is arrested together with his girlfriend at her home, where banknotes are found with a scent used to mark evidence collected by the police. The banknote serial numbers did not come from that day's robbery, but had been placed in police storage and signed out two weeks earlier by Callo. He is found shot dead in his home, together with incriminating evidence linking him to the heist.
When reviewing video footage from the bank, Dekker notices one corner of the bank is deliberately shielded from view. In that corner, they find the bank regional manager's computer. Fingerprints on the keyboard reveal the identity of a hacker that Conners himself had arrested, but whose conviction was overturned after the shooting on the bridge. Conners and Dekker want to question the hacker, but he is shot dead by Lorenz, and a gunfight ensues, during which Lorenz manages to escape. Dekker questions the hospitalized bank robber identified in the news footage and finally breaks him when he casually explains the impact of a massive overdose of morphine while slowly injecting something into the suspect's drip. An amazed Conners watches and later calls him a hypocrite. Dekker responds by explaining he only injected more saline solution.
The suspect reveals Lorenz is Scott Curtis, the brother of John shot earlier, and Conners leads a stakeout at an address where all the gang are to meet that night; Scott's house. Forced to go before Scott arrives, a shootout results in both suspects' deaths, and a bomb blows up the building while Conners is inside. Dekker is devastated but realizes that Callo's signature requesting material from the evidence storage was forged by the evidence custody officer, who reveals that Scott is actually York. In a flashback, York stands on the bridge and fires the first shot, killing the hostage in the opening sequence. Tracking Lorenz/York's mobile phone, Dekker surprises York at a diner, and York takes a woman hostage in a reversal of the standoff on the bridge. Dekker chases and eventually kills York.
When Dekker pays for his coffee at the diner, he discovers the banknote Conners used to pay for lunch with is also scented, which means Conners was also involved in taking the money from police evidence. Dekker finds a copy of James Gleick's Chaos: Making a New Science in Conners' house, showing he had faked an earlier ignorance of the mathematics. On a hunch, Dekker looks for airplane tickets booked in Gleick's name and runs to the airport.
During a mobile call between the now disguised Conners and the searching Dekker at the busy airport, flashbacks reveal how the seemingly unconnected events in the film form a pattern, just as predicted in chaos theory. Conners reveals that he placed his badge on the corpse of one of York's henchmen before the explosion. Conners and York recruited a group of ex-convicts from their past. Callo was framed for being a dirty cop. Conners ends the call, walks casually to a private jet, and takes off while sipping champagne.
