"Yeah," said Simms. "Be pretty stupid if we're caught now!"

The two men climbed down into the power deck and began the job of
refitting the freighter from chemical to atomic drive. Having already
outfitted the vessel with atomic engines, it was a simple matter to
change the exhaust, reset the feed lines, and emplace the protective
lead baffles. In an hour the two spacemen were ready to blast off.

"There she is," said Simms, standing back to survey their work. "As fast
as anything in space, except the Solar Guard cruisers on hyperdrive."

"O.K.," said Wallace. "Let's get out of here!"

Minutes later, in a jet car speeding along the main highway toward the
exposition grounds, Captain Strong, Mike Hawks, and the three cadets of
the _Polaris_ saw a rocket ship blast off. They watched it disappear
into the dark space above.

"That might be they," said Strong to Hawks. "I'd better alert the patrol
ship near the space station and tell them to pick them up."

"That couldn't be Wallace and Simms, sir," said Astro.

"How do you know, Astro?" asked Strong.

"That was an atomic-powered ship. The wagon Wallace and Simms have is a
chemical job. I know the sound of her jets almost as well as I do the
_Polaris_."

Hawks looked at Strong.

"You can depend on Astro's opinion, Mike," said Strong. "He was born
with a rocket wrench in his hand and cut his teeth on a reactor valve."

They soon reached the outskirts of the exposition grounds and were
forced to slow down as they wound their way through the darkened
streets. In the amusement section, the last of the whirlaway rides and
games of chance had closed down and only the occasional roar of a caged
animal in the interplanetary zoo disturbed the night.

Hawks drove the low, sleek jet car around the fair, taking a short cut
through the outdoor mercuryball field and pulled up in front of the
_Polaris_.

The five spacemen turned toward the concession site across the promenade
and stopped, aghast.

"Gone!" exclaimed Strong. "Astro, you made a mistake! It was their ship
we saw blasting off. It's too late to warn the space-station patrol.
Wallace and Simms could be anywhere in space now!"

"But, sir," protested Astro, "I'm certain that an atomic-powered ship
blasted off. And their old freighter was a chemical burner!"

"Well," said Hawks resignedly, "they're not here."

"Come on," said Strong, getting out of the jet car. "Let's take a look
around."

Strong and Hawks h