have wings.
Are mine sprouting yet?" And he turned his back to Roy for the
latter's examination.

When the laughter ceased, their leader went on, "You boys are to be
congratulated for your discovery. You have accomplished a great deal.
But what has been done is little compared with what remains to be done.
And so far you have worked in safety. The work ahead may be very
dangerous. The hidden wireless stations we are after are probably in
lonely places. The men operating them are desperate fellows and will
not hesitate even to commit murder. If one of you boys should follow
this motor driver into a lonesome spot and then be caught, you might
never return."

The smiles faded from the faces before him. But the grave looks that
succeeded were not expressions of fear. Rather they were looks of
determination--the same set marks of grim purpose that Captain Hardy
had seen on these same youthful faces when the wireless patrol was
stalking the desperate dynamiters at the Elk City reservoir.

Again it was Roy who brought back the smiles. "If we have to follow
that automobile driver," he said, "it's a question of 'where do we go
from here, boys?'"

"Only the boy who does the following can answer that question,"
answered Captain Hardy. "But there are several matters that we can
decide at once. I think that we've determined pretty definitely that
the man in the house below us----"

"In the hawk's nest," interrupted Roy.

"Well, the man in the hawk's nest," continued their leader, smiling,
"is a German spy, that he is there to report the movements of our
transports, and that he does it by means of messages sent out on silver
dollars. Now we've got to get hold of one of those dollars. That
might not be a difficult task in itself. We could hold up the grocer's
boy and take the dollar away from him, or we might get it away from him
by trickery and substitute another dollar for the stolen one. We might
even be able to pick the grocer's pocket and give him a substitute
coin. But neither plan would help us because the trick would soon be
discovered and the spies would know that they are suspected. It
wouldn't do us any good to get their code if they knew we had it. They
would simply use another. What we must do is to locate their agents,
one after another, learn their codes and ciphers, and catch their
messages in the air. When we have laid bare the entire scheme and
learned who their agents are, then the secre