o first, and then to Captain Strong, but it had
to be done secretly. He realized that his knowledge of the identity of
the saboteur would be a more effective weapon if everyone still believed
he was on Mars.

After getting close enough to the Academy to use the slidewalk system
crisscrossing the huge area, he loitered on the crowded platforms which
connected the hangar, the Academy, and the spaceport. He kept his coat
collar high and his civilian hat pulled low over his eyes.

He was on the main slidewalk, moving toward the Tower building, when his
eyes picked out the familiar close-cropped blond hair of Roger and the
unmistakable bulk of Astro on the walk leading to the hangar. Changing
at the slidewalk intersection, he took off after them, hoping he would
not be noticed in the crowd of civilian workers. Roger and Astro were
carrying tools over their shoulders and were lagging behind the main
body of workers moving toward a huge tunnel opening. Tom saw his chance
and moved up quickly beside them.

"Keep walking and don't show surprise!" he whispered sharply.

But it was too much to ask. Astro and Roger jumped in surprise and let
out involuntary shouts of joy, which attracted the attention of the
guards. They noticed the stranger in civilian clothes and stared at
him.

"Tom!" exclaimed Roger. "What the devil are you--?"

"Sh!" hissed Tom. "We haven't got much time." He saw one of the guards
turn and stare at him. "Listen to me," he continued quickly. "I've got
important dope about the saboteur!"

"How?" gasped Astro.

"Never mind," replied Tom. "Now, to nail him, I've got to get him into
the act! I need proof!"

"But who is it?" asked Roger.

"I can't tell you now. Here comes the guard. Are you going to be working
around here long?"

"At least another three days," said Roger. "But who--?"

Roger noticed the guard move up to them and he suddenly straightened up
and snorted derisively, "Yeah. But why a guy should want to join the
Solar Guard is more than I can see. You must be wacky, mister!"

He and Astro walked away, and after a hesitant look at Tom, the guard
followed the two cadets. Tom boarded the slidewalk heading back toward
the Academy. So far, so good. He knew where his unit mates were, but up
ahead, in the gleaming Tower of Galileo, was his second target, Captain
Strong. His skipper had to listen to him, had to be sympathetic and help
him catch the saboteur. It was the only way Tom could clear hi