For a moment all three were silent with amazement. “From California–and
Moon Base–for _us_?” gasped Burl, finally. “But why? What can they want
of us?”

His father frowned. “Only way to find out is to open it and see.” He
squatted down to study the cylinder closer. Burl pointed a finger at the
nose.

“Looks like a crack there. Maybe it unscrews. Let’s lift it.”

It was not as heavy as it had appeared, for, like all rocket missiles,
it was made of the light but tough alloys that were necessary to
conserve weight-lift costs and fuel reserves. They stood it upright and
tried to turn the top. After a little resistance, it unscrewed slowly.
Inside, they found a rolled document bearing the seal of the United
States Air Force.

Burl took it out, and unfolded it with unsteady hands. His father read
over his shoulder.

Gonzales poked at the empty cylinder, impatiently. Finally, he burst
out, “What does it say? What do they want?”

Burl turned to him. “It’s unbelievable! It’s–it’s just so darned
surprising! The dimness of the days, the drop in temperature–it wasn’t
just around here! It was all over the world!”

Quickly, he went on to tell the Peruvian what they had just learned. The
communication was from the U.S. Space Commission and it had been
directed on its 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 lonely and hostile
sky domains.

Panting and weary with hours of climbing, Burl and his father made a
quick lunch in a sheltered jumble of rock near the top. Then,
shouldering their packs again, they trudged on. At last they reached a
point where the view of the other side spread out before them–a
breathtakingly clear vision of the little valley below.

As they looked down, the air seemed to shimmer and vibrate. Burl rubbed
his eyes. “It hurts,” he said.

His father squinted. “There’s a powerful vibrational effect. It may be a
very dangerous concentration of the invisible rays of the Sun as well as
of light.”

Once Burl had gotten used to the odd visual effect, which was like
gazing into the twisting heat rays rising from an overheated oven, he
saw that there was a small flat region between the mountains. And in the
center of this valley was a large black structure of some sort. The
twisting effect of the light around it made it impossible to tell more.

“That’s it,” said Burl. His father nodded, shifted the pack to ease his
shoulders, unstrapped the hunting rifle slung over his back, and
carefully checked its loads.

Burl saw what his father was doing and suddenly understood the danger.
What could be doing a thing like this? What but something not of this
Earth? Something of distant space, of a science beyond that of man–and
_unfriendly_ besides. Now, for the first time, Burl realized what he had
not had time to before–this was an enemy he and his father were
facing–an enemy of all mankind–and utterly unknown.

He gulped, gripped his rifle, and followed his father down the sliding
rocky trail.

As they drew nearer the base of the mountain, the effects of the strange
vibrations grew more pronounced. Burl avoided looking directly ahead,
keeping his eyes on the ground before his feet, yet even so, he could
not help noticing how the stones around them seemed to shimmer in the
invisible waves. From the base of the valley the sky now seemed streaked
with black and gray rings, as if they were reaching the center of some
atmospheric whirlpool. Out of the mountains, after hours of arduous
scrambling, they started across the barren rocky plain.

Before them rose a vast circular structure several stories high,
ominously black and without any sign of windows or doors. Above the
building protruded two great projections ending in huge, shining discs.
One of the monstrous cuplike discs was facing the Sun, the other pointed
in the opposite direction.

As the two men came nearer and nearer, the strangeness in the air
increased. They felt they were being penetrated through and through with
invisible lances, with tiny prickles of heat. “Radiation?” queried Burl
softly, afraid of the answer. His father trudged grimly on for a
moment, and then put down his pack. He took out a Geiger counter and
activated it.

He shook his head. “No radioactivity,” he said. “Whatever this is, it
isn’t that.”

They reached the wall of the building. Oddly, here they seemed sheltered
from the unusual vibrations. Burl realized that the source was above
them, probably the two mighty discs raised high in the sky.

The Dennings surveyed the building, but found no entrance. It must have
been a quarter of a mile around its walls, but there was no sign of a
door or entry. The wall was of a rocklike substance, but it was not like
any rock or plastic Burl had ever seen.

“We’ve got to get in,” said Burl as they returned to the starting point,
“but how?”

His father smiled. “This way.” He opened his pack and took two cans of
blasting powder from it. “I thought these would come in handy. Lucky we
had some left over from the blasting we did last week.”

He set both cans at the base of the high wall, wired them together, and
ran the wire as far as it reached. When the two men were a safe distance
away, Mark sparked off the explosive.

There was a thunderous roar: rocks and dirt showered around them, and
bits of black powdery stuff. When the smoke cleared, Burl and his father
leaped to their feet, rifles in hand.

There was a crack in the side of the wall where the explosive had gone
off. And the rip was large enough to get through!

Without a word, they charged across the ground, still smoking from the
concussion, and squeezed through the mysterious walls of the enigmatic
building.

The walls were thin, thin but hard, as befit masters of atomic
engineering. Inside, they found a roomless building–one single chamber
within the frame of the outer walls.

A dim, bluish light emanated from the curving ceiling. On the uncleared
rocky ground which was the floor of the building were a number of huge
machines.

They were spherical glassy inventions, many times the height of a man,
connected by strings of thick metal bars and rows of smaller globes,
none of which was familiar. There was a steady humming noise, and above,
the two giant, metal masts penetrating the ceiling rotated slowly.
Doubtless, the great Sun-trapping discs were affixed to the top of these
masts.

There was no living thing in sight.

Burl and his father stood silently, half crouched, with rifles at the
ready, but nothing moved to challenge them. There was only the humming
of the Sun transmitters.

Burl called out, but there was no answer. They advanced cautiously,
fearing a trap. The place did not have the look of living things about
it. “An automatic station,” said Mark under his breath. “I think it’s
strictly automatic.”

It gradually became evident that Mark was right. Everything was
automatic. Whoever had built this structure to divert the rays of the
Sun had simply set it down, put it in motion, and left. There was no
evidence of any provisions for a garrison or a director.

They studied the machines but could make nothing of them. They found
what looked like controls, but although they pushed and pulled the
levers and knobs, the humming did not cease. It seemed as if the
controls were either dummies or had to be specially motivated.

“What do we do now?” asked Burl, after they had tried pulling all the
levers on one particular switchboard without any results. “Do you have
enough powder left to blow up the machinery?”

His father shook his head. “I had only those two cans with me. We could
try shooting into the machinery.” Leveling his rifle, he fired at a
glassy globe perched upon the central sphere. The bullet pinged off it,
and they saw that it had failed even to dent the glistening surface.

“It won’t work,” said the elder Denning, after several more shots had
produced the same result and the concussion reverberating from the
enclosed walls had nearly deafened them.

They continued to hunt for a clue, but found none. Dejected, Burl kicked
a loose pebble and watched it rattle against a column near the main
control board. A small metallic ball rested on top of the column,
apparently unattached. A replacement part, he thought to himself,
wandering over to it. It was about the level of his head.

With the thought that if he examined it he might learn something of the
nature of the working machines, he reached out with both hands to pick
it up.

As his hands touched the metallic ball, there was a sudden terrible
flash of power. He felt himself grasped by forces beyond his control,
paralyzed momentarily like one who has laid hold of an electrically
charged wire. He opened his mouth to scream in agony, but he could say
nothing. A great force surged through his body, radiating, charging
every cell and atom of his being. He felt as if he were being lifted
from the floor. Then the globe seemed to dissolve in his hands. It
became a glare of light, grew misty, and then vanished.

For a moment he stood there on tiptoe, arced with the potent violence of
the force, glowing from within with energies, and then he felt as if the
supercharge were dissolving itself, slipping into him, sliding into the
ground, then disappearing.

He stood before the column, swaying, but still conscious and alive. His
hands were still raised, but there was no ball between them, neither of
metal nor of power.

He let them fall to his side and took a step. He was whole, he was
sound, he was unharmed. He heard his father’s footsteps running to him,
and murmured weakly, “I’m all right.”

And he was. He could see no sign of damage. “I must have absorbed an
awful lot of that energy–or whatever it was,” he said.

After resting a moment, he decided to try the useless controls again.
Going over to one small board, he idly shoved a lever. This time he felt
resistance. The lever was activated. There was a slight change in the
radiance of one globe.

“Dad!” Burl shouted. “It works! It works for me now!”

Mark Denning watched as Burl turned dials and levers and got responses.
“You must have been charged in a special way,” he said excitedly.
“That’s how they lock their devices. They will only respond to a person
carrying that special energy charge, whatever it was. Come on, let’s get
to the main control, before the effect goes away–if it does.”

The two dashed to the panel which, they guessed, activated the main Sun
transmitter. Burl grabbed the instruments and threw them back to what
seemed to be the zero positions.

The humming rose in intensity, then quieted down and finally stopped.
There was a series of clicks, and one by one, the various globes,
condensers and glowing machines died out. Above them came a whirring
noise, and Burl looked up to see the masts withdrawing into the
building, their discs presumably left flat and directionless.

It felt different. Suddenly they knew that the vibrations which had been
so heavy in the air about them were gone. There was silence everywhere,
the natural silence of an empty, lifeless building in an uninhabited
valley.

Burl and his father made their way to the break in the wall and climbed
through it.

Outside, the Sun shone down brighter than it had before. The sky was
the calm serene blue of a cloudless day. Burl knew that at that same
moment, all over the world, the sky was clearer and the Sun warmer.

But for how long? Behind them the building still stood–and its
inventors were still to be found.