gun in the
center denoting their service as guards on the Rock was prestige envied
even by commissioned officers of the Solar Guard.

After what Tom thought to be the most thorough search he had ever seen
was over, Lieutenant Williams reported to the control deck where Strong
and the cadets had been politely but firmly detained. He informed them
that they were now ready to blast off to the Rock, adding that a more
detailed search of the area between the ship's outer and inner hulls
would be conducted after they had gone.

"You mean," said Tom, amazed, "that you actually search the four inches
between the two hulls? What in the universe could we possibly hide in
there?"

"I don't know, Corbett," replied Williams. "We've never found anything
there." He turned to Strong and smiled. "But there's always a first
time, isn't there, sir?"

"Yes, of course," agreed Strong. "You do a thorough job, Williams. Very
good indeed!"

"Thank you, sir," said Williams. "You know, we've heard about you and
the _Polaris_ unit here on the Rock." He turned to Tom, Roger, and
Astro. "We have a stereo of that mercuryball game you played at the
Academy when you were Earthworms."

"What?" cried Tom. "You mean that game was recorded?"

"It sure was," said Williams. "But we've seen it at least fifty times."

"Well, blast my jets!" said Astro in amazement.

The game was one that the cadets had played when they first entered the
Academy. It had done much to unify the boys into a fighting team.

An enlisted sergeant suddenly appeared, snapping to attention in front
of Lieutenant Williams. "Ready to blast off, sir," he said.

"Very well," said Williams, then turned to Strong and the cadets.
"Follow me, please."

In a few moments the space launch was blasting away from the freighter
and heading for a tiny planetoid in the distance. As they drew near,
Strong and the cadets peered out of the ports to get a view of the
prison, but were disappointed when Williams ordered the ports covered.

He smiled apologetically at Strong and explained, "All approaches are
secret, sir. We can't allow anyone to see where our defenses are
located."

"You fellows certainly believe in keeping prisoners in and visitors
out!" commented Strong.

"Anyone interested in coming to the Rock, sir," said Williams, "is under
natural suspicion."

The three cadets gulped, duly impressed with the severity of the prison
routine.

Soon they felt the unmistakable jar a