In 2003, former U.S. Marine Corps Force Reconnaissance officer John Creasy visits his old comrade Paul Rayburn, who runs a security firm in Mexico. Wealthy Mexico City businessman Samuel Ramos, and his American wife Lisa, hire Creasy to guard their nine-year-old daughter “Pita”. Samuel only hires Creasy to satisfy the requirements for kidnap and ransom insurance (K&R).
Creasy is a burnt-out alcoholic, and tries to commit suicide one night, but the cartridge fails to fire. He distances himself from Pita, but soon begins to bond with the kind and astute girl and subsequently starts working to control his drinking, having found renewed purpose in life.
One day, when Creasy waits for Pita outside her piano lesson, a group of thugs and two uniformed Policía Judicial Federal (PJF) officers kidnap her. Creasy kills four of the kidnappers, including the PJF officers, but collapses from multiple gunshot wounds as the abductors escape with Pita. Hospitalized, Creasy is charged for murdering the policemen and is suspected in Pita’s kidnapping. Miguel Manzano, the honest Director of the Agencia Federal de Investigación (AFI) fears Creasy will be killed by the PJF, and has Rayburn move him to a veterinary hospital.
The head of the kidnapping ring, dubbed “La Voz” (The Voice) from his many ransom calls, contacts Samuel with instructions to deliver a US$10 million ransom. Samuel’s attorney Jordan Kalfus and PJF Lieutenant Fuentes gather the ransom through the K&R policy, then deliver it to the kidnappers. The delivery, however, is ambushed by members of “La Hermandad” (The Brotherhood), a crime syndicate composed of PJF officers, who steal the money and kill The Voice’s nephew. The Voice notifies the Ramoses that as retribution for this, Pita will now be lost to them forever.
When Creasy wakes in the veterinary hospital, and learns from Rayburn about Pita’s death, he leaves to start his own investigation. Looking through her notebook for a suspicious license plate she once recorded, Lisa appears and approves of his intention to kill everyone involved. Rayburn helps Creasy purchase weapons and explosives. Journalist Mariana Guerrero, Manzano’s girlfriend, convinces Manzano that they should provide logistical support.
The license plate leads Creasy to Jorge Gonzalez, the thug he saw dragging Pita away. Gonzalez proves to also be PJF, revealing (when tortured by Creasy) that he is a member of La Hermandad. He gives Creasy information on the operatives involved in the next stage of the kidnapping. Creasy tortures and kills his way up La Hermandad’s chain of command until he reaches its “president”, Lt. Fuentes. Fuentes confirms that his men stole the money, but that the bags were missing $7.5 million of the ransom, which was last handled by lawyer Kalfus. Creasy then kills Fuentes.
Creasy finds Kalfus dead at home, and also finds evidence linking Kalfus and Samuel to the kidnapping. When he confronts the Ramoses, Samuel confesses that he agreed to Kalfus’ plan to work with The Voice to stage Pita’s kidnapping. He took $5 million to pay off gambling debts inherited from his father, splitting the rest between Kalfus and the Voice. Samuel killed Kalfus, holding him responsible for bringing Fuentes in and causing Pita’s death. An enraged Lisa demands that Creasy kill Samuel; Creasy instead leaves Samuel with a pistol and the misfired round, which Samuel uses to commit suicide.
Using information provided by Creasy, Manzano is able to identify the “Voice” as Daniel Sanchez, who Mariana then exposes on the front page of her newspaper. Creasy sneaks into the home of Daniel’s brother, Aurelio, finding Daniel’s pregnant wife and three of his children. Aurelio shoots Creasy, but Creasy tortures him and has the wife phone Daniel. Creasy threatens to kill all of Daniel’s family unless he gives himself up, but Daniel surprisingly offers to exchange Pita for Creasy himself. After Daniel is able to provide confirmation that Pita is alive, Creasy agrees to the demands. Creasy has Lisa meet him at the exchange, having her hold a shotgun to Aurelio’s head. Creasy and Pita embrace and briefly talk, then he makes her run to Lisa, who releases Aurelio while Creasy surrenders to the kidnappers. As Lisa and Pita drive away, Pita sees Creasy surrender to the kidnappers. Creasy succumbs to his wounds as Daniel and his men drive away with him. Manzano, knowing Pita is free and Creasy is dead, kills Daniel during his “arrest”.