As Gragg scrolled around the base of the building illustration, a rollover displayed the red, glowing outline of a door in the front wall. He looked up at the real wall some twenty feet ahead of him. He couldn't see any indication that there was a door in the plain cinder blocks. He hovered his mouse cursor back over the section of wall in the diagram, and a drop-down menu appeared. It had two selections: «Open» and "Close." Gragg clicked "Open."

In front of his car, he saw a section of the cinderblock wall move inward and then slide sideways-revealing a dark doorway about five feet wide. Gragg half expected roiling steam to emanate from the opening. It was outlined with a soft red glow.

Was this it? Was he supposed to enter? He looked around warily. That would require getting out of his car.

The spotlight from the building still shined down on the area, revealing what a horrendous morass of mud he'd driven into. He had no idea how he'd get the car out without a tow truck. He couldn't stay in here forever.

Gragg shut down his laptop and packed up all his gear. In a few minutes he had everything in his rucksack except for his Glock 9mm-which he kept in his right hand. Gragg opened the Tempo's driver door with its trademark 1980s-Detroit-crack-squeak sound. He gingerly placed one combat-booted foot into the quagmire and felt it sink up to his knee. He groaned in disgust, but realizing he had no choice, he followed it with his other foot, closing the car door behind him. Pretty soon he was stagger-stepping through the deep mud toward the dark opening in the cinderblock wall.

Gragg stopped and took another look at the smashed VW Vanagon with Louisiana plates and anarchy bumper stickers. Shattered taillight plastic and twisted side moldings littered the area. The left rear wheel of the VW was smashed into immobility, set at an angle to the axle. The passenger door of the Vanagon was slightly open, with deep footprints leading out of the mud and toward the road.

Gragg stood for a moment, deciding whether to check it out. He realized he didn't want to be walking around out here and continued staggering through the foot-sucking mud toward the building.

Before long he climbed up onto a ledge of solid ground that ringed the building. Gragg examined his legs. They were caked in mud. His feet were sopping wet. He tried to scrape the mud off his boots by dragging them against the ground but gave up and slung his rucksack over his shoulder. Then he chambered a round in the Glock and faced the opening.

Diffuse red light emanated from the edges of the door. It was just enough light to reveal a polished stone floor extending into the blackness beyond. Red. Low-frequency light not visible from any significant distance.

Suddenly a British-accented female voice spoke in midair right alongside Gragg's head. "Come inside, Mr. Gragg."

Gragg was so startled he reflexively squeezed off a shot with the Glock. The deafening crack echoed off into the sky. The bullet whined off the cinderblock wall, then howled out into the woods.

The female voice spoke again. It sounded slightly artificial, clipped. "Are you familiar with gunshot detectors? Police departments in major U.S. cities deploy them to identify and triangulate the precise location of gunshots the moment they occur. A gunshot has a distinct acoustic pattern. Even the weapon fired can be identified by its sound pattern. You apparently have a…nine millimeter." There was a pause. "You won't need it. You've earned the right to enter."

Gragg looked down at the Glock in his hand. He took a breath. He'd never felt out of his depth technologically, but the disembodied voice was as close to magic as he'd ever experienced. He didn't like the role of awed primitive. It didn't suit him. He took another deep breath and tentatively spoke to the voice. "Who are you?"

The voice shot back. "This door will close permanently in ten seconds."

Gragg's thoughts scattered, and he hesitated for a moment before rushing through the doorway and into the darkness-feet squishing mud. The moment he did so, the door slid noiselessly closed behind him. The red glow from the door frame faded away as the opening sealed shut. Gragg stood in pitch-black darkness for a moment. It smelled not at all musty. It was super-clean, dry, filtered air. He wasn't in South Texas anymore…

Suddenly a diffuse white light began to emanate from the walls. It didn't flicker on, like fluorescent lights, but steadily rose from nothing to a comfortable, even glow. It was confident, effortless light, and completely silent.

Gragg found himself in a room twenty feet square, with a single steel door set in the middle of the wall straight ahead of him. The door had a dappled gunmetal look to its surface, as though it were meant to draw the eye. The walls in here were all glowing white panels-made of some nylon or fiberglass material. The floor was simple polished concrete.

The voice came back suddenly, startling Gragg as it circled around him. Gragg was hearing it, but he was still having difficulty accepting it. In real life a voice couldn't appear in thin air. It wasn't possible.

"You've come a long way, and you've accomplished much." A pause. "Don't be frightened by my voice. Its appearance in midair is accomplished through a HyperSonic Sound system. This technology is commercially available. Would you like to hear a technical explanation? Yes or no?"

Gragg looked around at the ceiling and walls. There were tiny plastic pods of various sorts mounted there. He cleared his throat. "Yes."

"A HyperSonic Sound system-or HSS-does not use physical speakers. HSS pulsates quartz crystals at a frequency thousands of times faster than the vibrations in a normal speaker-creating ultrasonic waves at frequencies far beyond human hearing. Unlike lower-frequency sound, these waves travel in a tight path-a beam. Two beams can be focused to intersect each other, and where they interact they produce a third sonic wave whose frequency is exactly the difference between the two original sounds. In HSS that difference will fall within the range of human hearing-and will appear to come from thin air. This is known as a Tartini Tone-in honor of Guiseppe Tartini, the eighteenth-century Italian composer who first discovered this principle."

Gragg was feeling slightly faint.

"This is only the beginning of what you will learn. You do wish to learn, don't you?"

"Yes," he blurted.

"Then we must determine your sincerity."

The whir of a precise electrical motor came to his ears, and Gragg glanced around the room. A small console had opened up in the wall next to the door. Gragg warily approached it, his feet squishing mud onto the concrete floor. He saw no other muddy prints. He must have been the first to make it this far. A smile stole across his face, and he approached the console with more courage.

The console appeared to be an array of biometric devices-a handprint reader, a camera lens with a rubber viewfinder, and a microphone. There was also a small LCD screen-like the type found on the backs of airline seats. It was not illuminated.

The voice was right next to him. "Place either hand on the reader. Place your eye against the viewfinder, and adjust the microphone to a position approximately three inches to the right of your mouth."

Gragg did as instructed. It was not the most comfortable setup, but he didn't think complaining was a good idea.

"Very good. I can administer this test in one of seven different languages. Is English your primary language? Answer 'yes' or 'no.'"

Gragg cleared his throat. "Yes."

"Good. I am going to ask a series of questions. You must answer truthfully-even if you think the truth is not the optimal response. This is not a test of your skills as a hacker. It is an effort to determine if you bear us ill will. A pattern of falsehoods will terminate the test. Early termination of the test will cause the air to be pumped from the room. This will create a partial vacuum that will cause the nitrogen to bubble out of your blood-resulting in an excruciating death. An MPEG video of your death will be placed on the Internet as a warning to others. Do you understand? Answer 'yes' or 'no.'"