tors, and others.

Hour after hour, day after day, night after night, they listened in. A
week passed. Then another went by. But excepting for one or two
snatches of talk, seemingly innocent, the watchers at the wireless caught
nothing.

Then, as Roy was listening in one noon while his comrades were
down-stairs at luncheon, there was a sudden buzzing in his ear. Rapidly
he shifted coil and condenser until the vibrations came sharp and clear.
A call was sounding. 2XB was calling 5ZM. Roy seized his pencil and
copied the signals, at the same time trying hard to locate the direction
from which the signals came. It was well that Roy was a fast operator,
for the message that followed came with such rapidity that it taxed Roy's
ability to catch it. But he managed to get every letter. When the
message was ended, Roy reached for his list of stations and rapidly ran
through it. The stations he had overheard were not listed. There could
be no doubt about it. He had caught a message from a secret wireless.
He turned to the paper with the message. Here is what he had written
down: SRPSTSNIAOLTMIXNREHONTSTFIRG. But he could make no sense of it.
The letters would not form themselves into words, combine them as he
would. He rose and ran to the dining-room with the paper.

Captain Hardy studied it for an instant. "Take this at once to Chief
Flynn," he said. "He may want to ask some questions about it. Willie
will relieve you at the wireless."

Several hours passed before Roy returned, and Captain Hardy began to fear
lest, despite the training in the geography of the city, Roy had become
confused and gotten lost. Then suddenly the door of the wireless
apartment burst open and Roy flew in.

"Chief Flynn told me he thought his men could unravel that message and
that I should wait a while," panted Roy, breathless from running up the
stairs. "And they did get it. It's what they call a transposition
cipher. Here is what it says."

He held out a sheet of paper. On it the letters Roy had picked out of
the air were arranged in four lines, as follows:

S R P S T S N
I A O L T M I
X N R E H O N
T S T F I R G

"Read down instead of across," explained Roy.

Captain Hardy studied the cipher a moment more, then read aloud: "Six
transports left this morning."

CHAPTER VI

A NEW DANGER POINT

For a moment there was dead silence. Then Captain Hardy spoke. "You
have done excellent work, Roy," he sa