Proofed by an unsung hero.

Above the horizon-spanning desert of Crockett County, Texas, lightning flashed against the sunset. Black thunderheads, touched by red and amber, stood like mountains against the sky.

Sudden raindrops splattered on the windshield of the Dodge. Al Horton, Federal Bureau of Investigation field agent, switched on the wipers. The rain died away as quickly as it had come. Horton flicked off the wiper switch and rolled down the window. The scents of rain and dust and mesquite filled the car.

Two miles ahead on Highway 10, silhouetted against the bloodred western sky, the semi-tractor trailer maintained a steady eighty miles an hour.

Horton glanced at a road map. He eased off on the accelerator. A thin, balding man, forty-three years old with a master's degree in public administration, a father of three children, Horton had no interest in tailgating a truck that was loaded with high-explosive ammunition.

The bureau's San Antonio office had issued a detailed directive to the four agents secretly tailing the truck:

Follow the shipment of weapons and ammunition. If the truck stops, radio the coordinates. If the truck stops at an airfield, radio the coordinates, wait for backup. If the truck nears the Mexican border, radio the coordinates, wait for backup. Under no circumstances attempt to arrest the occupants or seize the truck's cargo.

They didn't need to tell us that, Horton thought, smiling to himself. Four middle-aged office men with pistols and shotguns against gunrunners with automatic weapons? Right, boss, no heroes this week.

In the rearview mirror, Horton saw the headlights of the second car. He nudged his partner.

Lou Butterfield awoke, startled. He stared around blinking at the landscape of sand, creosote bushes and cactus that blurred past the car. "What's happening? Have they stopped?"