come back."

"By the craters of Luna!" Connel suddenly exploded. "The Solar Guard
spends a fortune to develop a foolproof space torpedo and two hot-shot
cadets come along and get away from the blasted thing! Why haven't you
told this to anyone before?"

"Why--er--" stammered Tom, "we've never had the chance to prove it,
sir."

Behind them, the power-deck hatch suddenly opened and Astro stepped in.
"Nice work, Tom!" he called.

"And as for you, you Venusian ape," roared Connel, "don't you realize
that you can blow a reactor tube by throwing so much power into a ship
without energizing the cooling pumps first?"

Astro smiled. "Not if you open the by-pass, sir," he said, "and feed
directly off the pump reservoir. The gas cools the tube and at the same
time expands itself and adds to the power thrust."

At Astro's easy reply Connel could only stand openmouthed in
amazement. Again, one of the three cadets of the _Polaris_ unit had
developed a revolutionary procedure that even top rocket scientists
would be proud to call their own.

Winking at Tom, Astro turned away and suddenly noticed Barret sprawled
on the deck, unconscious.

"What happened to him?" asked the big Venusian.

"Oh, I forgot all about him," said Tom. "Guess he didn't get into an
acceleration chair in time. Better get some more water."

"We haven't time for him now!" snapped Connel. "Strap him in good and
tight. We've got to find out where that torpedo came from."

As though in answer to the major's order, there was a sudden call over
the ship's intercom.

"Radar bridge to control deck, check in!" There was a note of alarm in
Roger's voice.

Tom jumped to the control panel to reply.

"Control deck, aye!" he snapped into the microphone.

"There's a spaceship to starboard!" called Roger. "Distance twenty
miles, fifteen degrees up on the plane of the ecliptic. And I swear
she's maneuvering to fire another torpedo!"

"Stand by action stations!" roared Connel, diving into his chair before
the control panel. Tom strapped in next to him, while Astro made a
headlong dash for the power deck.

"Yes!" shouted Roger. "She's fired a torpedo!"

"Raise her! Raise her!" bellowed Connel. "Tell them who we are!" He
turned to Tom. "Go into your act, Corbett," he said, "and make it good!"

As Tom manipulated the controls again, the silver ship plunged through
space, turning and gyrating in the same series of maneuvers it had
performed to escape the first