k
reports they've got a clogged line, sir. It's in the gas exhaust."

Strong and Hawks looked at each other, and then Hawks turned to the
young officer. "Send a couple of men outside to clear it."

"Aye, aye, sir," said Claude, and then hesitated. "Shall the men wear
lead suits against possible radioactivity, sir?"

Before Hawks could answer, Newton turned to face the three men. The
professor was smiling. "No need to take that precaution, Lieutenant. I
never did tell you my third opinion, did I, Captain Strong?"

"Why, no, you didn't, sir," said Strong.

The professor held up a sheet of paper. "Here's your answer. Nothing but
plain old Venusport topsoil. Pure dirt!"

"What?" exclaimed Hawks hastily, reaching for the paper.

"Well, blast me for a Martian mouse," muttered Strong under his breath.
"But how?"

Newton held up his hand. "Don't ask me how it got here. That isn't my
line of work. All I know is that, without a doubt, the black cloud is
nothing more than dirt. Plain ordinary dirt! And it comes from the area
in and around Venusport. As a matter of fact, certain particles I
analyzed lead me to believe it came from the exposition site!"

Hawks looked at Newton dumbfounded. "By the craters of Luna, man, we're
a thousand miles over the exposition!"

The professor was stubborn. "I can't tell you how it got here,
Commissioner Hawks. But I do know it's Venusian dirt. And that's final!"

Hawks stared at the elderly man for a second, still bewildered. Then he
suddenly smiled and turned to Claude. "As soon as that exhaust is
cleared, blast off for Venusport, Lieutenant. I'm going to find out who
dirtied up the sky!"

* * * * *

Two hours later, when Captain Strong returned to his hotel in Venusport
with Mike Hawks, he was surprised to see the three cadets of the
_Polaris_ crew slumped, sleepy-eyed, on a couch in the lobby.

"What are you doing here, boys?" he asked.

The three cadets came to attention and were wide awake immediately. Tom
quickly related their suspicions of Wallace and Simms.

"And we've watched them every night, sir," Tom concluded. "I don't know
what it is, but something certainly is going on in that shack they use
for an office."

"Yes, sir," agreed Astro, "and no one is going to fool me about a rocket
ship. I know when they blast off loaded and return light."

Strong turned to Hawks who said quietly, "Wallace and Simms are the only
ones in this whole a