Next airing Fri Mar 16, 5 p.m. ET

Hidden Tunnel

In the southern border towns of Douglas and Nogales, Ariz., agents fight a constant battle to stem the flow of illegal immigrants and drugs. With 100 miles of mostly open desert between the two cities, crossers and smugglers constantly attempt to slip through. At the ports of entry, Border Patrol's successful campaign to uncover record amounts of hidden drugs and stowaways has only emboldened others to attempt more cunning methods to avoid detection, including a drug tunnel under the border.