amount of sunlight reaching the arid, airless surface of the Earth's
only satellite.

The cause was somewhere on Earth. And the Security Council requested the
careful scanning of the Earth from space platforms and the Moon to
determine the center of the trouble.

* * * * *

Burl Denning had not found the next valley of much interest, either.
Evidence of an Inca road over the mountain had petered out. There were
signs there had been human dwellings, but they were not Inca--just
reminders of the onetime passage of an unknown band of primitives who
had grazed their sheep, built temporary tents, and pulled up stakes
perhaps a hundred years before.

So again at night, Burl, his father, and Gonzales took counsel. They
were debating which way to proceed next; Mark Denning reasoning that
they should go further inland, following tales natives had told;
Gonzales urging that they retrack their path and proceed northward
toward the regions where Inca ruins abounded.

For the past week Burl had not been able to get radio reception. The
static had increased as they had gone eastward over the mountain, but
not a word of news or any human voice came through. The Moon was rising
on the horizon as Burl sat playing with the antenna. Finally he gave up
and switched it off.

The discussion had died away and the three men were quiet. The Indian
guides had retired to their own campfire, and one of them had taken out
his pipes and was blowing a soft, plaintive tune.

Burl stared at the full Moon in silence, wondering if he would ever have
a chance to walk its surface, or if his own future was to lie in probing
mankind's past rather than surveying the grounds of his future. As he
watched, he thought he saw a faint light among the brightening stars
where none had been before.

He squinted, and, sure enough, he saw that one tiny white light was
swinging more and more toward the center of the sky. He pointed it out
to his father and Gonzales. "Too fast to be a celestial object," he
said. "Is it one of the space platforms or a sputnik?"

The two men gazed at it in curiosity. Suddenly it seemed to grow
brighter and sharper and to twist toward them in its path.

"Look!" gasped Burl, but the others were already on their feet.

The light plunged down. There was a sudden outburst of yellow flame that
caused the three to duck instinctively, and brought the Indians to their
feet with yells. The glare brightene