Set in the tumultuous Border area of Arizona and Mexico, Frontera follows the events that take place after a former Arizona Sheriff's wife (Amy Madigan) is killed while riding on their Ranch property. It would appear a Mexican man (Michael Pena) crossing in to the US illegally is at fault. As former Sheriff (Ed Harris) and current Sheriff (Aden Young) search for answers, lives are changed forever and the facts as to who is really at fault in this tragedy are nearly as tenuous and complex as the issues and tensions between the people who live in this region on either side of the line.