Jack (George Clooney), an American assassin, is relaxing in a remote cabin in Sweden with his lover, Ingrid (Irina Björklund). The two decide to take a walk on the frozen lake nearby. While walking, Ingrid notices some footprints. Jack quickly drags her to cover behind a boulder as someone begins shooting at them. He kills the shooter and then tells Ingrid to return to the cabin and phone the police while he searches the body. As she rushes past him, he shoots her in the head. Returning to the cabin, he kills another assassin.
A few days later, Jake arrives in Rome, Italy where he contacts an associate named Pavel. Pavel insists that Jack cannot stay in Rome and sends him to a small town in the mountains of Abruzzo. Jack becomes nervous, and, disposing of the cell phone which Pavel had given him, flees to another town. While he is hiding out there, Jack is befriended by an elderly priest, Father Benedetto (Paolo Bonacelli), who pressures him to seek absolution, something which Jack, now going by the name 'Edward' and posing as a photographer, resists.
Jack contacts Pavel, who sets him up with another job. He meets with a shady Englishwoman, named Mathilde (Thekla Reuten), who wants him to build a gun with the firing capacity of a submachine gun and the accuracy of a rifle. Jack begins work on the weapon as he begins patronizing a local prostitute, named Clara (Violante Placido). At the same time, Jack realizes that he is being followed by the same people who tried to kill him in Sweden.
One day, Jack meets with Mathilde to test the weapon he has made in the nearby forest. She asks for a few more alterations to it. While having coffee one day, Jack bumps into Clara and a friend, named Anna. Clara invites him on an actual date, and the two begin to deepen their relationship. One night, an assassin follows him, but Jack manages to hide. Just when he is about to shoot the man from behind, a man comes by on a motorscooter, alerting the assassin who fires, missing Jack but killing the motorcyclist.
Jack chases the man to a road outside of town and kills him. He is questioned about the incident by Father Benedetto. Soon Jack begins to become suspicious of Clara when he finds a gun in her purse and sees her meeting with some men. He takes her on a picnic where he plans to kill her but cannot bring himself to do it. Clara explains that she has the gun because of a number of assaults on prostitutes which have occurred in the area, and that the men she was talking to were cops investigating the case.
After talking to Pavel one last time, Jack agrees to deliver the weapon to Mathilde as his last job. At the drop off, Jack becomes suspicious that Mathilde plans to kill him when she excuses herself to go to the bathroom. Before anything can happen, a busload of people arrives, giving Jack cover, and the two go their separate ways. While driving away, Mathilde is contacted by Pavel, who asks if she has killed Jack. She informs him no but insists that she is following Jack and will kill him. Pavel cleary wants Jack dead either because of the Sweden foul-up or because he does not want any loose ends since nobody leave his murder-for-hire organization, and Mathilde is the hitwoman assigned by Pavel to kill Jack.
Jack meets Clara in the crowd at a local religious festival. He asks her to go away with him and she joyfully agrees. Meanwhile, Mathilde is lurking on a nearby rooftop, with Jack in the sights of the weapon he has just delivered to her.
However, when she fires at him, the weapon misfires, injuring her fatally. Previously.... before he delivered the weapon to her, we see him opening the case after a pause, leaving us to assume he booby trapped the gun to misfire... aware that she is the assasin trying to kill him. Jack, hearing the rifle shot, tells Clara to go to the place where they had picnicked and wait for him. He then chases after Mathilde, followed by Father Benedetto and several alter boys who had been part of the procession. He find Mathilde dying on the pavement and asks her who she works for. She dies before she can reveal anything, and Jack leaves, apologizing to Father Benedetto.
As Jack leaves he sees Pavel, who had arrived earlier. The two have a shoot out, and Jack kills Pavel. As Jack drives to meet Clara at the picnic spot by the creek, he discovers he is bleeding and realizes he has been wounded. As he arrives at the picnic spot, Clara smiles with joy, but Jack loses consciousness and crashes into a nearby tree... maybe dead.