A group of Mexicans is attempting to cross the Mexican-American border. They are hunted by Sam (Jeffrey Dean Morgan), a Confederate flag-waving vigilante armed with a shotgun. Sam, with his loyal dog at his side, is determined to protect his country from foreign invaders and sets out to kill the Mexicans one at a time. Moises (Gael García Bernal), the reluctant leader of a dwindling group, must rely on luck and wits to outmaneuver his more knowledgeable and ruthless opponent.