Daemon

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 cinder-block 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 thewalls. 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 Giuseppe Tartini, the eighteenth-century Italian