e, evidently
in search of possible intruders. The boys crouched lower behind the
bushes and prayed fervently that Jimmy would not arrive before the man
had gone. The fellow was of fair size, with a deeply tanned face, and
wore a moustache. Fortunately, after they had been watching him a few
minutes, he removed the earphones, placed them in the box, and, after
locking it, started into the woods, following a dimly marked footpath.

It was well that he left when he did, for not two minutes later Jimmy
came puffing along, looking anxiously for the others. He stopped in
amazement when he saw his friends emerge from the bushes, and was about
to raise his voice in vehement questionings when Bob leaped at him and
clapped a hand over his mouth.

"Be quiet!" he hissed into his ear. "There's some funny work going on
here, and we want to find out what it is."

Thus admonished, Jimmy was released, and in low tones the others told
him of what they had seen and showed him the box fastened to the tree.
While they were about it, they made a hasty search for the antenna, and
found it strung close to the trunk of the tree, extending from the top
almost to the roots. After this discovery they hurried after the man
with the moustache, fearful lest they should lose his trail.

It was no easy matter to follow the dimly marked path, for it passed at
times over stony ground and big boulders, where often it took much
searching here and there before they picked up its continuation.

"We may be taking all this trouble for nothing," said Bob, after one of
these searches. "Maybe he's just a lumberman receiving instruction by
wireless from his employers. Big business firms are using radio more and
more for such purposes."

"I didn't like the way he kept looking about him, as though he had
something to conceal," objected Joe. "It can't do any harm to see where
he goes, anyway. We may find out something important."

"His hands weren't those of a lumberman," observed Herb. "Those hands
never saw rough work nor, judging from the man's face and manner, honest
work. Come on, fellows."

Accordingly the boys followed the difficult trail with untiring
patience, and at last their perseverance was rewarded. The path widened
out into a little clearing, and at the further side of this was a rough
log cabin. The little shack had two small windows, and with infinite
caution the boys approached until they could see into the nearest one.

The interior was r