His forehead crunched with tension, he scanned the radar imagery in front of him. On screen, the hedgehog and the men surrounding it showed up as color-coded shapes positioned against a set of grid lines and numerical coordinates.

"This doesn't make any sense," Jezoirski said. "There's nothing to show the outer fence was breached--"

"We can worry about that later." Cody was already reaching for the phone as he broke his silence. "Key the 'hogs for full gamut intruder suppression. I'm getting Thibodeau on the horn."

On Jezoirski's radioed command, Wally hit them with a barrage of light and sound.

Its first optical counterstrike was a burst from the neodymium-YAG laser projector on its turret. To the four men around the robot, it seemed almost as if a small nova had ignited at ground level, momentarily filling the night with diamond-edged brilliance.

They scattered rapidly, fanning out over several yards--but the flash was something for which they had come prepared. They had known that a laser pulse could temporarily impair the vision or burn out the retina, dazzle or blind, depending on its power, intensity, and length. They had also known that the weapons used by Sword's robotic defenders were calibrated to produce no lasting damage. And they had worn dark filters on their visors to shield them from the brightness, correctly betting this would make its effects tolerable.

The hedgehog's sensory assault, however, was about to kick into overdrive. The laser flash had barely faded in the air when a group of red-and-blue halogen lights on Wally's main equipment case began to strobe in a preprogrammed sequence, its pattern and frequency closely matching that of normal human brain waves. At precisely the same instant, the robot's acoustic generator had begun transmitting 100-decibel soundwaves at a controlled rate of ten cycles per second. It was a resonance the invaders seemed to feel more than actually hear, a sour, abrasive humming that remained just below the level of audibility, working its way deep into their bodies, swelling thickly in their stomachs and intestines.

Each directed-energy weapon worked on the same principle, targeting specific areas within the human body, coupling the spectrum of its emission to characteristic waveforms within those areas, and manipulating them by hyperstimulation. The flashing lights attacked the visual receptors of the hindbrain, triggering a storm of electrical activity akin to the sort that occurred during a sudden attack of epilepsy. The acoustic generator had multiple targets--the inner ear, where abnormal vibrations of the fluid within its semicircular canals would throw the sense of balance into upheaval, and the soft organs of the abdomen, where similar vibrations would lead to convulsions of pain and nausea.

The combined effect of these measures overtook the invaders at once, scrambling their senses and motor functions, confusing and sickening them, provoking a hallucinatory and physically wrenching disconnection from their surroundings. Shaking, gagging, and retching, they staggered in confused, purposeless circles. One of them dropped onto his back, his bladder releasing, grotesque herky-jerky spasms running through his limbs. Another sank to his knees, clutched his heaving stomach, and vomited.