r copper and other ores about a half mile above the Wiley
claim. I was in charge of operations. That is how I know the ground so
well. One of our northern leads broke through into a tunnel of the
abandoned mine. When copper prices were shot to hell in the depression
of 1930 we quit taking out ore; but when I went through the place
eighteen months ago it was still possible to crawl from one mine to
another. Of course earth and rock may have fallen since then, but I
don't believe the way is yet blocked. If I were dropped in that
vicinity at night with another man and the necessary tools and
explosives...."

The general thought swiftly.

"An auto-gyroscope could land you all right. There's one here now. But
what about the second man to accompany you?"

Manuel said quickly, "I'm going with the boss."

"You, Manuel," Talbot said roughly. "Don't be a fool. If anything
should happen to me--well, I've lived my life; but you're only a kid."

Manuel's face set stubbornly. "An experienced mining man you need, is
it not? In case there should be difficulties. And I am experienced.
Besides, senores," he said simply, "my wife and child are somewhere in
those mountains ... above Oracle...."

Talbot gripped his hand in quick sympathy. "All right, Manuel; come if
you like."

A moonless sky hung above them as they swung over the dark and
jungle-engulfed deserted city of Tucson, a sky blazing with the clarity
of desert stars, and to the south and west shot through with the beams
of great searchlights. Flying at a lofty altitude to avoid contact with
drifting globes or betrayal of their coming with no lights showing
aboard their craft save those carefully screened and focused on the
instrument board, it was hard to realize that the fate of America,
perhaps of the world, hung on the efforts of two puny individuals.

Everything seemed unreal, ghost-like, and suddenly the strangeness of
it all came over Talbot and he felt afraid. The noiseless engine made
scarcely a sound; the distant rumble of gunfire sounded like low and
muttering thunder. They had come by way of Tucson so as to pick up a
ten-gallon tube of concentrated explosive gas at the military camp in
the Tucson mountains.

"This gas," the general had assured them, "has been secretly developed
by the chemical branch of the War Department and is more powerful than
TNT or nitro-glycerin. It is odorless, harmless to breathe and exploded
by a wireless-radio device."

He had