Walking the Line offers a harrowing view of the chaos, absurdity and senseless deaths of Mexican illegals along the U.S. - Mexico border because some American citizens are taking the law into their own hands. Southern Arizona, a region celebrated for its history of lawlessness, has become the most highly trafficked area for immigrants in the world -- and one of the most dangerous. A shift in the border policy forces migrants to cross the unforgiving desert where thousands die. Those who make it across face volatile, often armed, civilian militias. Standing in opposition to the vigilantes are humanitarians, organized to prevent migrant deaths. Confronting the growing crisis, they too find themselves on the wrong side of the law. A Tucson pastor is indicted on federal felony charges for aiding and abetting while a Native American faces banishment from his reservation for constructing water stations. Following rancher vigilantes with semiautomatic weapons, outlaw pastors with four-wheel drives, and impoverished immigrants armed only with dreams of a better life, the film explores the uncertain line between what is patriotic, what is moral, and what is just.