alk could
mean the difference between life and death in space where you seldom got
a second chance.

Tom and Connel arrived on the jet-boat deck to find Astro already
preparing the small space craft for launching. As they struggled into
space suits, Roger appeared. In answer to their questioning looks, he
explained laconically, "Unidentifiable object attached to ship on fin
parallel to steering vanes. Thought we'd better go outside first and
examine later."

Connel nodded his mute agreement, and thirty seconds later the tiny jet
boat was blasting out of the escape lock into space.

Circling around the ship to the stern, the jet boat, under Major
Connel's sure touch, stopped fifty feet from the still glowing, exhaust
tubes. He and the three cadets stared out at a small metallic boxlike
object attached to the underside of the stabilizer fin.

"What do you suppose it is?" asked Astro.

"I don't know," replied Roger, "but it sure doesn't belong there. That's
why I rang the emergency on you."

"You were absolutely right, Manning," asserted Connel. "If it's
harmless, we can always get back aboard and nothing's been lost except a
little time." He rose from the pilot's seat and stepped toward the
hatch. "Come with me, Corbett. We'll have a look. And bring the
radiation counter along."

"Aye, aye, sir!"

Tom reached into a near-by locker, and pulling out a small, rectangular
box with a round hornlike grid in its face, plunged out of the hatch
with Major Connel and blasted across the fifty-foot gap to the
stabilizer fin of the _Polaris_.

Connel gestured toward the object on the fin. "See if she's hot,
Corbett."

The young cadet pressed a small button on the counter and turned the
horn toward the mysterious box. Immediately the needle on the dial above
the horn jumped from white to pink and finally red, quivering against
the stop pin.

"Hot!" exclaimed Tom. "She almost kicked the pin off!"

"Get off the ship!" roared Connel. "It's a fission bomb with a time
fuse!"

Tom dove at the box and tried to pull it off the stabilizer, but Major
Connel grabbed him by the arm and wrenched him out into space.

"You space-blasted idiot!" Connel growled. "That thing's liable to go
off any second! Get away from here!"

With a mighty shove, the spaceman sent Tom flying out toward the jet
boat and then jumped to safety himself. Within seconds he and the young
cadet were aboard the jet boat again and, not stopping to answer Ast