they saw a bare, unshaded lamp suspended from the roof of the tunnel.

Tom suddenly stopped and jerked Astro back. "Look!" he exclaimed,
pointing to the floor, not two paces away. A thin wire, hardly
noticeable, was stretched across the floor at ankle height.

"That bright light is to attract your attention while you trip over that
thing and probably blow yourself to bits," he said grimly, pointing to
the wall where the wire was connected to a small charge of explosives.
"Nothing to bring the roof down," he continued, "but enough to blast
whoever tripped over this wire."

Stepping over the wire carefully, they started down the shaft again, but
Tom paused thoughtfully.

"What's the matter?" asked Astro.

"That booby trap," said Tom. "We'd better not take any chances of
tripping over it on the way back. We might be in a hurry."

"I know what you mean," grunted the big Venusian. He knelt down beside
the menacing box of explosives and quickly disconnected the trip wire,
throwing the box to one side.

Straightening up, Astro announced, "It's harmless now."

Cautiously the two cadets continued down the tunnel, the roaring sound
growing louder and louder. After twenty minutes, Astro paused, his
homely features wrinkled in a frown of worry.