tion."

"We won't need it," Mr. Perry smiled. "These two guns are enough."

The purchase completed, the two men and the boy left the store and
hastened on toward the municipal docks.

Meanwhile Max arrived at his home and went direct to his radio room.
There the first thing he did was to don his phones, and the result was
instantly startling.

He had left the instrument tuned to the Friday Island wave length and the
aerial switch in receiving position.

"S O S, S O S, S O S," crashed into his ears in rapid, energetic, excited
succession, it seemed to his susceptible imagination.

Quickly he threw over the switch, and called for an explanation. It came
as follows:

"Those men have seized my friend, and now are coming after me. S O S, S
O--"

That was all--not another dot or dash. Desperately Max appealed for
further details, but it was like calling for life in a cemetery. The
ether was dead, so far as Friday Island was concerned.

CHAPTER XX

Four Prisoners

When the Catwhisker arrived at Friday Island again, the place appeared to
be deserted.

The camp was as they had left it, except that the breakfast dishes were
washed and put away. "Friday" had performed his duty, but both boys had
disappeared, and there seemed to be only one explanation of their
disappearance, namely, the premonition of danger at the hands of the four
strange men that the Rockport amateur, Max, had received from the boys on
the island. No damage had been done to the tent or any of the camp
paraphernalia, even the radio outfit being exactly as it had been when
they left it in charge of Hal and Bud a few hours previously.

"This is getting pretty serious," Mr. Perry said, after they had made an
unsatisfactory review of the situation. "I confess I don't know what to
make of it."

Cub felt an impulse to brand this new affair as the most puzzling mystery
that had yet confronted them, but he checked the utterance wisely enough
as entirely too facetious for the occasion.

"We've got to get the authorities busy on this case," Mr. Perry added
after a few moments' hesitation. "We may be sure now that it's more than
a hazing affair. There must be a retreat of some bad men around here
somewhere."

"What authorities shall we ask to help us?" Cub inquired.

His father seemed about to answer, but he hesitated a moment or two, with
a puzzled look, first at his son, then at Mr. Baker.

"That's so," he said presently. "Where are we--in