The movie begins at a diner in Upstate New York, as a woman called Mallory Kane (Gina Carano) sees a man drive up outside and utters the word “shit”. The man, Aaron, (Channing Tatum), orders her to get in his car. She refuses, and they fight, with Aaron nearly capturing Mallory before the intervention of a customer called Scott (Michael Angarano) allows her to break Aaron’s arm, knock him unconscious, and escape with Scott in Scott’s car.
Mallory tells Scott that both she and Aaron are contractors with a private firm that is employed by the American government for covert operation assignments. One week before, at a meeting among the firm’s director (and Mallory’s ex-boyfriend), Kenneth (Ewan McGregor), government agent Coblenz (Michael Douglas) and his contact, Rodrigo (Antonio Banderas) the firm was retained to rescue a man called Jiang (Anthony Brandon Wong), who is being held hostage in Barcelona. Mallory and her team, which includes Aaron, succeed in rescuing Jiang and delivering him to Rodrigo.
Shortly thereafter, Mallory is approached by Kenneth who offers a mission which he promises will be “like a two day vacation” — pose as the wife of a British agent called Paul (Michael Fassbender) during a mission in Dublin. Mallory agrees and accompanies Paul to a party at Russborough, a stately home near Dublin, where they meet with his contact, Studer (Mathieu Kassovitz). Paul meets with Studer again as Mallory watches from afar. She sees Paul going into a barn and enters it after he leaves to find Jiang dead, clutching in his hand a brooch which Paul and Kenneth required her to wear as a recognition signal for her initial contact with Paul.
Mallory realizes she has been set up and returns to her hotel room, where she’s attacked by Paul. They fight, Mallory gets the upper hand and shoots him dead. Mallory calls Kenneth and as he picks up the phone, he asks, “is the divorce final?” Although Mallory doesn’t speak, Kenneth knows she’s using Paul’s phone. As Mallory leaves her hotel, a SWAT team appears to arrest her but she escapes after a chase and manages to enter the United States and reach the diner, where she meets Scott.
Mallory calls Coblenz who tells her that he has had suspicions about Kenneth for some time. Coblenz then contacts Kenneth and tells him to inform Mallory’s father, John Kane (Bill Paxton), (who already knows of his daughter’s occupation), of her crimes. Meanwhile, on the road, Mallory and Scott are chased by the police and hit a tree after a deer runs into Scott’s car. They are both arrested, but soon the convoy is ambushed by assassins sent by Kenneth. Mallory escapes, kills the assassins, and releases Scott. She gives him a number to call for protection and leaves to meet with her father.
Mallory reaches her father’s house in New Mexico before Kenneth, Aaron, and two additional men arrive to interrogate John on his daughter’s whereabouts. Aaron starts to realize that Mallory might have been set up and tries to press Kenneth for the truth, but Kenneth kills Aaron as Mallory takes out Kenneth’s men.
Mallory chases Kenneth, but he escapes. The following day Mallory meets with Coblenz, who reveals that he ordered Kenneth to contact Mallory’s father so she could kill him there. Mallory asks Coblenz to fix things with Scott, which he promises to do, and is informed of Kenneth’s location. Before leaving, she is also offered a government job, but replies only that she’ll let Coblenz know when she finds Kenneth.
In Mexico, Mallory confronts Kenneth at the beach and they fight. Kenneth is clearly outmatched and tries to escape, but gets his foot jammed between two rocks. Kenneth reveals that Jiang was a journalist who had written a series of articles exposing Studer’s crimes. Knowing that Mallory planned to leave his firm, Kenneth arranged for her to rescue Jiang and deliver him to Rodrigo, who then delivered him to Studer, who killed him. Kenneth then framed Mallory, planning to cut all ties that could lead to him by convincing Paul that Mallory was a double agent whom he should kill. Mallory leaves Kenneth to drown in the incoming tide for his betrayal.
Rodrigo is enjoying his “retirement” in Majorca. After his female companion is called to the door and he goes to investigate her failure to return, Mallory descends from the roof onto the balcony behind him. When Rodrigo turns and sees Mallory, his response is simply, “Shit,” and the film ends with the last word of dialog being identical to the first word of dialog.