The film revolves around an assassination plot on President of the United States Henry Ashton (William Hurt), who is participating at an anti-terrorism summit in Salamanca, Spain. The entire movie is based on a single, short period of time, which is retold six times, each time from the viewpoint of different characters. By the end of the film, each character's story comes together to tell the true story of what really occurred.
Rex Brooks' perspective
The first perspective is that of television news producer Rex Brooks (Sigourney Weaver), who directs various "GNN" cameramen and news anchors as the President arrives. Brooks catches sight of a familiar face in the President's Secret Service detail: that of agent Thomas Barnes (Dennis Quaid), who had taken a bullet for the President in an assassination attempt six months before. The mayor of Salamanca gives a short speech, then introduces the President. Just as the President steps up to the podium and raises his arms to the crowd, he is shot twice. An explosion in the distance at a hotel soon follows, propelling the crowd from confusion to panic. A few minutes later the podium itself is destroyed by another huge explosion. As the smoke clears, GNN's news reporter Angie (Zoe Saldana) is filmed lying apparently dead until Brooks kills the feed.
Thomas Barnes' and Kent Taylor's perspective
The second perspective is that of U.S. Secret Service agents Thomas Barnes (Dennis Quaid) and Kent Taylor (Matthew Fox). While the mayor is speaking, Barnes notices a fluttering curtain in a nearby building. He also spots a tourist, Howard Lewis (Forest Whitaker), with a video camera. After the President is shot, Barnes tackles a man rushing the podium, who is then dragged off by other agents. Barnes insists on viewing the footage on Lewis' video camera. Lewis thinks he might have caught the assassin on tape. Taylor pursues the assassin, offering to protect Barnes from blame in case he is wrong about the shooter. Barnes sees something on Lewis' video that alerts him to a possible bomb under the podium but is unable to alert anyone before it goes off. After the explosion, Barnes spots a TV cameraman. He barges into the production room and orders Brooks to show him GNN's footage. Barnes talks by phone to Taylor, who reports being in hot pursuit of the suspect. Barnes attempts to reach the Secret Service Command Post (with call sign "Control"), but does not get a response. Off a live GNN camera feed, Barnes catches sight of something which shocks him. He runs out.
Enrique (Eduardo Noriega) is a Spanish police officer assigned to protect the mayor of Salamanca. He spots his girlfriend (Veronica) being embraced by a stranger (Javier) and overhears them speaking about a meeting under a nearby overpass. When he confronts her, she assures him of her love. She asks if he has brought her bag and Enrique hands it over. When the President is shot, Enrique rushes onto the stage to protect the mayor and is tackled by Agent Barnes. In custody, Enrique watches his girlfriend toss the bag under the podium. He yells: "We are all in danger, we have to go now!" Enrique escapes after the podium explodes, and the agent who had him in custody chases him across the city, ultimately failing to catch him. He confronts someone unseen at the overpass, asking if they are surprised to see him still alive.
Howard Lewis' perspective
Lewis (Forest Whitaker) is an American tourist who thinks he’s captured the shooter on his video camera while recording the event for his family back home. While waiting for the President to speak, he makes small talk with a man named Sam and is accidentally bumped into by a little girl named Anna, causing her ice cream cone to fall to the ground. He offers to buy the girl a new one but her mother declines. He notices Agent Barnes looking at a window and aims his camera at it. After the President is shot, Lewis films the pandemonium. Barnes runs up asks to see the film; both see Veronica throw a bag under the podium. Lewis picks up Anna, who has become separated from her mother, while chasing Enrique and the pursuing agents. Dropping the child off with a female Spanish police officer, Lewis resumes the chase. At the overpass Enrique speaks to someone out of Lewis' line of sight. The pursuing Secret Service agents open fire and Enrique collapses, mortally wounded. A single policeman crouches beside the body. Lewis then spots Anna, who has run away from the police officer. She sees her mother on the street's other side and starts to run toward her, much to Lewis' horror. As an ambulance bears down on the child, Lewis runs out in an attempt to save her.
President Ashton's perspective
Unknown to the public and GNN, it is a body double of Ashton that has been shot. Having been informed of a credible assassination threat, the President (codenamed POTUS) has returned to his hotel and is waiting for his double to give his speech. The president's advisor, Phil McCullough, advocates an attack on a terrorist camp in Morocco that he claims to be linked to the present threat. Watching on television, Ashton sees his double walk to his seat and says comically, "He doesn't even look like me." Ashton spots Tom Barnes in the double's security detail, ostensibly to test Barnes' state of mind before returning him to the real President's detail. When the body double is shot, the immediate reaction of his advisors is to coordinate with the Joint Chiefs of Staff to authorize the attack on the Moroccan camp. The President refuses, citing his desire to go on with the summit and expressing his belief that such an act of retaliation would be the response those who orchestrated the attack are hoping for. The distant explosion that was previously heard is revealed to be a bomb that has exploded in the hotel's lobby. Seconds later, a masked assailant bursts in and shoots the guards and advisors with a silenced pistol. He points the pistol at the President.
The Terrorists' perspective
The final perspective is that of the terrorists, beginning with their leader, Suarez (Saïd Taghmaoui), shown earlier in the film as Sam, the native that Lewis spoke to in a friendly conversation. The conversation was merely a way for Suarez to make sure Lewis didn't see anything about their plan on his camera and to hide in the crowd and draw any potential attention away from him. The assassination attempt on the double was an elaborate ruse, done by remote control using an automatic rifle. The rifle was retrieved by Agent Taylor (after Taylor told Barnes he was going to pursue the assassin alone). On the live feed in the GNN control room, Barnes sees Taylor leaving the scene in a Spanish policeman's uniform — even as Taylor is telling him over the phone that he is in pursuit of the assassin. Barnes concludes that Taylor has "gone rogue".
Although Enrique assumed his girlfriend Veronica was being embraced by another man, from the terrorists' perspective it is learned that Javier (Edgar Ramirez) actually was handling her with anger because she (with her partner) was holding his brother hostage in order to ensure Javier's cooperation. Javier has Special Forces training, which allows him to force his way into President Ashton's room. Javier takes the President to the elevator, where Veronica is waiting with a stretcher. Ashton is drugged and quietly loaded into an ambulance, with Suarez driving, by Veronica and a "GNN" camera man who is revealed to be working with the terrorists. Shortly afterward the camera man is murdered by Veronica. Javier joins Taylor in a police car. Barnes commandeers another car and carries out a chase through the city. Barnes' car is T-boned by a truck, allowing Taylor and Javier to get away.
At the overpass, Enrique confronts Javier. (Enrique, the "patsy" in the assassination plot, did not die in the blast at the podium as intended, and knows of the rendezvous at the overpass.) Javier apparently believes Enrique knows where his brother is being held; each pulls a gun, whereupon Javier shoots Enrique. Javier then is shot by Barnes as he tries to flee. As he clings to the door of Taylor's car and demands to see his brother, Taylor remarks "He's dead" and shoots him in the chest. Barnes fires several rounds at Taylor, wounding him. Taylor crashes his car and is killed. At the same time, Ashton comes to in the ambulance and attacks Veronica, distracting them just as the little girl, Anna, enters their path. Suarez swerves and the ambulance tips over just as Lewis pulls Anna out of the way. Barnes runs to help. He sees Veronica dead with a gun next to her. Ashton is alive. Suarez is also and raises his gun, but Barnes shoots him first. Ashton is then rescued by Barnes.
The film concludes with Lewis on the phone with his wife and kids. The audience discovers this elaborate plot is not going to be made public. Instead, according to a TV news report, the incident was caused by a lone assassin who has been killed by police.