In New York City, Nick Cassidy (Sam Worthington) checks in to the Roosevelt Hotel under the false name of Walker, goes to his hotel room at the top floor, and climbs on the ledge, apparently ready to commit suicide. The crowd below sees him and calls the police. They isolate the area, with Dante Marcus (Titus Welliver) controlling the crowd, while Jack Dougherty (Edward Burns) tries to talk with Nick. However, Nick says he will only speak to negotiator Lydia Mercer (Elizabeth Banks), who is on a leave of absence after failing to convince a depressed policeman not to jump from the Brooklyn Bridge a month earlier.
Lydia arrives at the hotel room and manages to acquire Nick's fingerprints from a cigarette they share. Dougherty has them analyzed and discovers that Nick is an ex-policeman who was arrested for stealing a $40-million diamond from businessman David Englander (Ed Harris). Nick has escaped from prison, where he was serving 25 years for the heist, after being allowed to attend his father's funeral a week earlier. Nick, however, says he is innocent and reveals that Englander used to employ cops to protect his multi-floor jewelry business. One day, while Nick was escorting Englander and the diamond, he was knocked unconscious by two men in ski masks. He awakened to find that Englander had framed him for stealing the diamond in order to get the insurance money, as he had lost his fortune during the stock market crisis.
Unbeknownst to the police, Nick is merely distracting them while his brother Joey (Jamie Bell) and Joey's girlfriend Angie (Genesis Rodriguez) break into Englander's upper floor jewelry vault in the building across the street to steal the diamond and prove Nick's innocence. Meanwhile, Dougherty informs Marcus of Nick's identity, and Marcus orders the security of the jewelry store to check the vault. Although Joey and Angie are able to evade them, they don't find the diamond. They set off the alarms, tricking Englander into retrieving the diamond from another safe that they did not know about, and return to his office, where they ambush him and steal the diamond at gunpoint. Note: The elements of a man on a ledge serving to cause a distraction to aid a jewel heist also appear in the episode of the Peter Gunn TV series episode "The Leaper" written by Robert Blees (first aired Dec. 29, 1958).
Meanwhile, Nick's ex-partner, Mike Ackerman (Anthony Mackie), arrives at the hotel with evidence that Nick is planning something and demands to be allowed into the hotel room. Lydia does not trust him, and Dougherty backs her up. Ackerman claims he has found bomb schematics in Nick's hideout and is convinced that he will detonate an explosive somewhere. While the crowd is evacuated by the anti-bomb squad, Lydia, believing in Nick's innocence, calls Internal Affairs and discovers that three of the cops employed by Englander were suspected of being corrupt; a deceased officer called Walker, Ackerman, and Marcus.
Englander calls Marcus, one of the men who helped him frame Nick, and has him capture Joey and Angie, but they have already given the diamond to a hotel concierge who passes it to Nick as he is being chased by the tactical team throughout the hotel. Marcus chases Nick to the roof where he orders Lydia to be arrested for obstruction. Englander brings Joey and Angie, and threatens to throw Joey off the roof if Nick does not give him the diamond. Nick does, and Englander leaves. Meanwhile, Lydia escapes custody and rushes back to the roof.
There, Marcus holds Joey at gunpoint in order to force Nick to jump off the roof, silencing him, when Ackerman arrives and shoots Marcus who in turn shoots back at Ackerman, wounding him. Nick rushes to Ackermn's side, and Ackerman apologizes, claiming that although he helped Englander to fake the diamond's theft, he never knew Nick would be framed. Marcus survives as he is wearing a bulletproof vest and is preparing to kill Nick when Lydia arrives and shoots him.
Nick jumps from the roof onto an air mattress set up earlier by the police, catches up to Englander before he enters in his limo, beats him, and pulls the missing diamond from his pocket, revealing the truth. Englander is arrested, while Nick is proved innocent and released after intervention by the governor. He meets Joey, Angie, and Lydia at a bar, where he introduces Lydia to the hotel concierge, who is Nick's father - having faked his death in order to help his son. Joey proposes to Angie with a diamond ring stolen from Englander's vault, and they all celebrate together.