erator's voice came through, the radio set
exploded in Tom's face!

CHAPTER IX

THE CAVE MONSTER

"Skipper!" Bud cried anxiously as Tom staggered back, his hands to his
face.

"I'm all right--no harm done," Tom assured his friend.

Both boys were a bit shaken by the accident, nevertheless. Chow came
rushing in as Bud was brushing the fragments of debris from Tom's
clothes and examining the young inventor's face.

"Brand my flyin' flapjacks, what happened?" Chow asked. The chef had
been bringing a tray of fruit juice to the laboratory and had heard the
explosion outside.

"The radio set just blew up in my face," Tom explained. "Fortunately,
the equipment was transistorized mostly with printed circuits.
Otherwise," he added, "I might have been badly cut by slivers of glass
from the exploding vacuum tubes."

As it was, the young inventor had suffered only a few slight scratches
and a bruise on the temple from a piece of the shattered housing. Bud
swabbed Tom's injuries with antiseptic from the first-aid cabinet while
Chow poured out glasses of grape juice.

"What caused it, Tom?" Bud asked as they paused to sip the fruit drink.

"Good question," Tom replied. "Frankly, I don't know." But he was
wondering if the set might have been sabotaged.

Tom was still eager to get in touch with his father and telephoned the
electronics department to bring another set to his laboratory. Chow left
just as the new set arrived.

Tom hooked it up quickly, donned a set of goggles, and tuned to the
space-station frequency. Then he picked up the microphone and stepped
well back from the set, waving Bud out of range at the same time.

"Tom Swift calling Outpost!... Come in, please!"

A moment later came another explosion! _The new set had also blown up!_

"Good night!" Bud gasped in a stunned voice. "Don't tell me that's just
a coincidence!"

Tom shrugged. "We can certainly rule out the possibility that anything
was wrong with the radio itself. Every set is checked before it leaves
the electronics department."

"So where does that leave us?" Bud persisted.

Tom shook his head worriedly as he took off the goggles. "Both times it
seemed to happen just as the reply was coming through from the space
station. There is no possibility that their signal was too strong--in
other words, that the explosion was caused by overloading the receiving
circuits."

"Are you implying that an enemy intercepted the message and sent s