"Maybe," I muttered. "Surely there must be something physical."

"How so?"

"The tunnel car must be full of it," I said. "Screws?"

I turned to Saul Graben. Saul is our mechanical genius; give him a sketch made on used Kleenex with a blunt lipstick and he will bring you back a gleaming mechanism that runs like a hundred-dollar wrist watch.

But not this time. Saul shook his head.

"What's permanent is welded and what's temporary is snapped in with plug buttons," he said.

"Good Lord," I said. "There simply must be something!"

"There probably is," said Saul. "But this Harla chap would have to use an acetylene torch to get at it."

I turned to Teresa. "Can this psi-man Harla penetrate metal?"

"Can anyone?" she replied quietly.