S2, E11: National Geographic's ripped-from-the-headlines Border Wars special, Murder on the Lake, explores Mexico's drug war and confronts one of the most serious threats to American security today. Our cameras return to the scene of David Hartley's murder on the otherwise placid looking Falcon Lake, and retrace his final hours through the eyes of his grieving widow Tiffany. Expert interviews explore how David's suspected murderers, the Zeta cartel, operate along the Texas/Mexico border, funneling drugs and illegal immigrants northward-ready to kill anyone who strays into their path. David's murder has brought into focus the growing fear that the violence may be heading north.