he was serious. "What is it?"
he asked.

"Why, in the name of the moons of Mars, would Barret want to do the
things he did to us?"

"Simple," said Roger, beginning to sweep industriously as he saw the
guard walking toward them. "He didn't like the way we manhandled him."

"You think he was just getting even with us?" asked Astro, also resuming
work.

"What else?" asked Roger. "We made him look pretty silly. And that was
no love tap I gave him that night we caught him in the hangar."

"That's what I mean," said Astro. "I know Major Connel said he was
supposed to be there. But with that teleceiver conversation I overheard
and all the rest--well, I just don't get it," he concluded lamely.

"You'll get it in the neck if you don't watch out," said Roger. "Here
comes Spike and he doesn't like to see us loafing!"

The two cadets worked steadily for ten minutes, and when the guard
finally walked away, they paused to watch the big ship again.

"I wonder what Tom is up to?" said Roger thoughtfully. "He said he knew
who the saboteur was, but he needed help to prove it."

"I'd give a full year's leave just to get my hands on that guy for ten
minutes," said Astro.

"Yeah," grunted Roger. "Well, come on, hot-shot, we still got a lot of
cleaning to do."

They returned to their work, but even then, as they watched the
preparations for the take-off of the big ship, they both thought about
Tom. They knew his problems were as difficult as their own, and with
much more at stake. If Tom failed in his efforts to catch the saboteur,
it could very well mean the end of the _Polaris_ unit.

[Illustration]

CHAPTER 16

"_Bump-ty--bump-ty--bump-ty--_"

Tom Corbett's heart beat with such rapid, heavy drumming that the young
cadet felt as though it was going to tear itself right out of his chest.

For nearly six hours Tom had lain in wait in Galaxy Hall, the museum of
Space Academy, on the second floor of the Tower building. He was hiding
in the tail section of the _Space Queen_, the first rocket ship to
breach space safely, blasting from Earth to Luna and back again. He had
kept watch through a crack in the hull of the old ship, waiting for the
lights to go out, a signal that the Academy had bedded down for the
night.

Now, in the silence of the museum, surrounded by the ancient objects
that traced man's progress to the stars, Tom felt like crying. For as
long as he had been at the Academy, he had revered these crude,