NOTE: This spoiler was written and submitted by Spectre.
George Clooney's character uses two names; Jack his real name and Edward his cover name. To avoid confusion I will refer to him as Jack.
The film opens in the snowy Swedish countryside. In a cabin in the woods Jack (George Clooney) is sharing his bed with Ingrid his girlfriend. Though distant with her, it is clear he loves her. Getting dressed to take a walk in the snow, Jack notices footprints on the ground and becomes paranoid. His suspicion are true, when he spots a sniper in the distance with a rifle trained at them. Jack pulls out his own gun and kills the assassin. Ingrid is shocked and confused, and Jack orders to go back to the cabin and call the police. When she turns her back to him, he shoots her apparently for knowing too much. Jack gets the drop on the second assassin and takes a ferry to leave. Though he shows little emotion, he is clearly shaken over killing a woman that was not only innocent but loved him.
Jack arrives in Rome and contacts his handler Pavel. Pavel meets him and asked if Ingrid sold him out. Jack denies it, saying she knew nothing. Pavel tells him to lay low until he can figure out why the Swedes came after him. He gives him a car, a cell phone, and a small town to hole up in. Jack goes but sees the people are particularly nosy at his arrival and he needs anonymity. Jack travels to a nearby town and dumps the cell phone Pavel gave him.
Setting up shop in the town, Jack surveys the surroundings and tries to stay anonymous. However, a local priest Father Benedetto (Paolo Bonacelli), takes a liking to him and coerces him into having drinks and conversation.
A few days later, Jack contacts Pavel. Pavel is mad about Jack changing his safe house and dumping the cell phone. Still, Pavel talks to Jack about a weapons design job. Jack says he'll think about it.
Jack winds up meeting his contact Mathilde (Thekla Reuten) and they discuss her necessary weapon. Jack thinks she has a second man with her, but he disappears before he can pointed out to Mathilde; she insures she came alone.
Jack picks up the materials for the post office and begins to assemble the rifle. The same night he meets up with a local prostitute Clara (Violante Placido).
Over dinner with Father Benedetto, Benedetto implies that he knows Jack isn't who he says he is. Benedetto also speaks of a young car mechanic Fabio that he is fond of (later revealed to his son).
Jack creates some damages to his car to justify a visit to Fabio's garage and asks for some tools. Jack takes them to create a suppressor for the rifle. He tests it out, and seems to be satisfied.
In between all this, Jack is still keeping his guard up, concerned that the Swedes are still after him. He begins to spend more time with Clara who he doesn't see as a prostitute and she doesn't consider him a client.
Jack meets with Mathilde so she can test out the rifle. She is satisfied though asks for some tweaks and special bullets.
Jack goes out one night and realizes he is being followed. He manages to kill the assassin, and calls Pavel to ask why they knew he was here. Pavel says Jack is getting soft.
Jack's relationship with Clara continues to deepen, even though he knows he cannot really stay. However, when Clara suggests they run away, Jack changes his mind. He calls Pavel one last time, telling him he'll do the drop for the rifle and then he's out. Pavel agrees to let him go. Pavel calls Mathilde and gives her special instructions.
Jack meets Mathilde for the drop and is nervous that he is being set up. However, he gets his final payment and leaves. Pavel calls Mathilde and asks why Jack isn't dead; Mathilde responds there wasn't an opportunity. It is here we realize that Pavel was the one who set the Swedes after Jack; he felt he was getting too comfy in a regular life with Ingrid and decided to terminate a liability.
Jack meets Clara at a religious festival. Pavel is in the town as well to make sure Jack dies. Nearby, Mathilde has killed a woman and climbed onto the roof of her house to get ashot at Jack. She fires the rifle, but it misfires, causing it to blow back on her. Jack had deduced after the third Swede assassin that Pavel had something to do with it and wanted to insure he wasn't next. Jack approaches a dying Mathilde and asks who she works for. She responds "Same man." before dying. Jack gives Clara the money for the job and tells her he will meet her at the spot he took her to.
Jack runs off with Pavel not too far behind. Jack realizes someone is behind him and turns to fire. Pavel gets a shot off but Jack fires twice, hitting Pavel in the head.
Jack drives off to meet with Clara, only to realize he has been shot by Pavel. He slams his fist against the wheel; he realizes he won't make it.
Jack gets to the spot and raises his bloody to Clara who realizes something is wrong. Just as he arrives he slumps over the wheel, dead, blaring the horn. Clara runs to the car horrified. The last shot pans away from the car to a shot of the tree skyline and a small white butterfly.