YOU COULD HEAR the tension over the radios.

As the Afghan border guards helplessly listened to the crackle of gunfire and the sharp, frantic voices of there brethren under attack at another distant post, American troops made a call to their base for air support.

After four bloody hours of fighting, the rebels loaded onto a truck and drove a few hundred yards over the unmarked border into the safety and sanctuary of Pakistan. In the end, two Afghan allies lay dead with two more badly wounded and an assault force of up to 100 Taliban-affiliated fighters slipped away to refit, rearm, and plan for more attacks unmolested in the lawless western border region of Pakistan.

That was back in April of 2004, near a remote border checkpoint east of the Afghan city of Khost. This volatile area--which was a primary transit point for anti-Soviet mujihadeen fighters in the mid-1980s--flanks one of the most contentious enclaves in the region. The so-called tribal areas of North and South Waziristan, just over the mountainous border with Pakistan, have been the launching points for violent attacks against U.S. and Afghan forces for years, but have remained largely "no-go" zones for American--and Pakistani--forces.

In that eastern frontier of Afghanistan, the bad guys come over the border, past seemingly oblivious Pakistani guards, ambush American forces and other Afghan or coalition troops, then run back over the border into the sanctuary of the tribal areas. Rumors of bin Laden and his chiefs' taking shelter there are commonplace, but few details

In the Frontline season premier airing this evening on PBS, award-winning documentary producer and journalist Martin Smith delivers an unprecedented view of a terrorist breeding ground that has apparently replaced Taliban-run Afghanistan. "Return of the Taliban" is a frightening look into the medieval madness and violence of the tribal areas--where disloyal elders are beheaded in the public square and thieves are hanged in the streets with money stuffed in their gaping mouths for all to see--should serve as a wakeup call to anyone who thinks America's enemies are in retreat.

Ask any military commander in Afghanistan where he thinks the threats are coming from and he'll tell you they're from the tribal areas of Pakistan. Though the Pakistani government issues vociferous denials that it harbors al Qaeda on its soil--with Pakistani president Pervez Musharraf recently declaring that al Qaeda's leadership is hiding in Afghanistan (which has more than 20,000 U.S. troops) not in Pakistan's tribal areas (which now has zero Pakistani troops on patrol)--the Frontline documentary provides strong evidence that powerful terrorist leaders such as Jalaluddin Haqqani and Nek Mohammed have been allowed to thrive in the tribal areas.

Incorporating vividly unsettling video footage and in-depth interviews with key players in the region, Smith paints a grim picture of a situation that seems to be slipping further from America's grasp.

"Arresting him might be something we will have to do," says one Pakistani official interviewed in the Frontline documentary of Haqqani. "But I'm not sure whether we know where he is, or whether we are capable at this time."