"La Mera Frontera" is a meditation on the border and memory which takes as its point of departure the last battle between the United States and Mexico. In 1918, neighbors from the border towns of Nogales, Arizona and Nogales, Sonora shot at each other for a day. Among the many citizens who lay dead was Maria Esquivel, who "returns" in the present to interview surviving witnesses, all now 80 to 90 years old. As a stymied historical detective Maria wrestles with the failure of Nogales' citizens' accounts to coalesce or recollect her and her absence in the local archives and films. Unable to uncover her past, Maria takes history into her own hands.