e they saw globes that glowed with the same intensity as those in
the Sun-tap stations had. They moved carefully now, keeping out of
sight, and several times they saw shadows in the distance or heard the
thump of something moving.

They worked their way by instinct to what they guessed was the center of
operations. They peered, at last, through a low, wide doorway into a
large chamber. Here was a mass of mighty globes and rods, some revolving
as they circled the metal masts that came through the room from the
ceiling above.

"It must be the base of the Sun-tap receiver line," whispered Haines.
"This should be a good enough place to set up our time bomb."

They stole over to a cluster of globes and unpacked the powerful little
atomic bomb they had carried with them. They carefully put it together,
inserted the explosive fuse, and set the timer. "I'm giving it four
hours," said Haines. "Time for us to get out of here and radio the
_Magellan_ to get into action. That should take care of this station."

They moved carefully out again, scarcely breathing for fear of some
Plutonian entering and discovering them. They made their exit safely
enough and started to retrace their steps.

Back down through corridors and strange chambers they moved, stopping
every little while as something that sounded like footsteps passed over
them. "Where," Burl whispered, suddenly troubled, "is the stolen heat
and power of the Sun going? It isn't heating up Pluto. Surely they can't
simply store it."

"Something we haven't solved," Russ replied hurriedly. "From what I
remember of the masts, it looked as if they were relaying it somewhere
else again."

"Can't imagine where," said Haines. "Not back into space, surely?"

They fell silent, concentrating all their energies on not losing the
way. "Are you sure we came through here?" Burl asked nervously. "I don't
remember this at all."

"I don't, either," said Russ. "It looks queer. Are you sure we're on the
right path?" He turned to Haines.

The explorer shook his head. "We must have made a wrong turn. I think
we've lost our direction."

They hastily conferred, and decided the best thing to do was to make
their way to the lowest level and then outward--but suddenly they
realized they could not tell which way was outward. There were no
windows, and the wall markings and direction signs were unintelligible.

To make matters worse, they heard new noises, and, just as they dodged
into a cor