The US-Mexican border is a unique meeting point of the first and third worlds. Every day thousands of Mexicans run the gauntlet of the US Border Patrol to reach the promised lands of California and Texas. On the Mexican side half a million people, mainly young women, earn a dollar an hour or less, toiling for US companies in the assembly plants. In On The Line, Augusta Dwyer journeys through the crowded, dirty cities of the border, uncovering the stories of dozens of ordinary Mexicans - workers, illegal migrants, environmental activists. She reveals the hidden costs of free trade, and shows how Mexicans are resisting exploitation and the destruction of their environment.