flight from California by the Moon Base, because only
from the satellite could the exact location of the Dennings be spotted.
It seemed that the Dennings were the only scientifically trained
personnel close to the point on Earth where the disturbance originated.
This also accounted for the blanketing of radio waves in their vicinity.
Several airplanes had tried to locate them, but strange disturbances in
the ether and atmosphere had made it impossible to establish contact.
Also, the back reaches of the Andes were poorly mapped and treacherous
in air currents, even in normal times.

"During the last week, a certain fraction of the Sun's light and energy
reaching the Earth has been diverted. It has been bent or focused in
much the same way that a lens bends light rays--and the point to which
it has been directed is a spot only seven miles from here! Over that
last mountain range," said Burl, pointing.

Gonzales followed his finger. "Just over the mountains lies the source
of the trouble," said Burl excitedly. "And we're the nearest to it. They
want us to go over there, see what it is, stop it, or report back. It
took the telescopes in Moon Base to locate us and to track the center of
the trouble!"

Mark Denning pursed his lips. "We'll have to start tomorrow, and we'll
have to go fast. A loss of light and heat, however slight, could have
very serious effects on life if continued too long. We can make it by
tomorrow night, if we start early and leave the Indians and pack animals
behind."

The other two nodded. Mark looked at them in the half-light of the Moon.
"You'll have to stay with the equipment, Pedro, otherwise the Indians
might abandon it. Burl and I will start out at dawn."

Gonzales agreed and the three made their way back to the camp. At the
first sign of light breaking in the morning horizon, Burl and his father
started off. They carried only enough equipment for survival, plus the
additional items that might be needed for the emergency ahead.

The trek over the mountains was a hard one, the path narrow, steep,
sometimes nonexistent. There were few signs of Indians or animals, and
it was plain that few ever traveled over this range. The air was cold
and thin, vegetation sparse and hardy. All around them was the cold
blue of the sky--a shade darker than usual--and the gaunt peaks of
ancient mountains. The Inca kings may have claimed the land here, but
even their hardy legions had never conquered these lonel