They climbed out of the car into sweltering heat. Ling's eyeglasses clouded over. He wiped them on his shirt. Peterson walked around the truck. "Can I get the unit without the truck?"

"Yes, we make transportable units. Seagoing containers. But usually clients want them mounted on vehicles eventually."

"I just want the units," Peterson said. "Are you going to demonstrate?"

"Right away," Ling said. He gestured to the operator, high up in the cab. "Perhaps we should step away."

"Wait a minute," Peterson said, suddenly alarmed. "I thought we were going to be alone. Who is that?"

"That's my brother," Ling said smoothly. "He's very trustworthy."

"Well amp;"

"Let's step away," Ling said. "We can see better from a distance."

The cavitation generator fired up, chugging loudly. Soon the noise blended with another sound, a deep humming that Ling always seemed to feel in his chest, in his bones.

Peterson must have felt it, too, because he moved back hastily.

"These cavitation generators are hypersonic," Ling explained, "producing a radially symmetric cavitation field that can be adjusted for focal point, rather like an optical lens, except we are using sound. In other words, we can focus the sound beam, and control how deep the cavitation will occur."

He waved to the operator, who nodded. The cavitation plate came down, until it was just above the ground. The sound changed, becoming deeper and much quieter. The earth vibrated slightly where they were standing.

"Jesus," Peterson said, stepping back.

"Not to worry," Ling said. "This is just low-grade reflection. The main energy vector is orthogonal, directed straight down."

About forty feet below the truck, the walls of the canyon suddenly seemed to blur, to become indistinct. Small clouds of gray smoke obscured the surface for a moment, and then a whole section of cliff gave way, and rumbled down into the lake below, like a gray avalanche. The whole area filled with smoke and dust.